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TARA (Cæsalpinia spinosa):

The sustainable source of tannins for innovative

tanning processes

Author:

Joan Carles Castell Escuer

Universitat Politècnica de Catalunya (UPC). Barcelona

Directors:

Dr. Anna Bacardit

Dr. Lluís Ollé

Doctorate program:

Engineering in projects and systems

Department of Project Engineering

Barcelona, January 2012

Thesis to obtain the title of Doctor from the Universitat Politècnica de

Catalunya (UPC) with international mention.

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Erratum:

Section 10, figures 49, 50, 51, 52, 53, 54, 56, X-Axis, NaCOOH instead NaCOH.

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Abstract:

This thesis considers the fruit of the tara tree (Caesalpinia spinosa) as a sustainable source for

tanning agents and proposes alternatives to the commercial mineral salts and vegetable extracts

to comply with an increasing demand that concerns lower carbon footprint and health safety.

Taxonomy of the tree is described and the substances contained in the fruit are chemically

characterized in order to justify that tara farm forestry is economically viable and to secure a

potential worth. The value chain is fully described from fruit collection in remote Andean

regions to the export for the most important leather markets.

Although tara tannins have been used in the leather industry and its properties being well

known, the experimental part of the work aims to optimize innovative formulations using tara as

wet-white pre-tanning agent. Combinations with a selected syntan used for wet white and final

article recipes are proposed.

Key words: Tara, tannins, leather, wet-white, vegetable-tanning, sustainability

Resumen:

Esta tesis considera el fruto del árbol de tara (Caesalpinia spinosa) como fuente sostenible de

taninos para la curtición del cuero y propone alternativas para las sales minerales y los extractos

vegetales como respuesta a la creciente demanda para reducir el impacto medioambiental y la

seguridad de los artículos de consumo. Se describe la taxonomía del árbol así como la

caracterización de su fruto para justificar la silvicultura como práctica económicamente viable y

asegurar su valor y la cadena desde la recolección de los frutos en las regiones andinas hasta la

exportación a los mercados más importantes de la industria del cuero.

Aunque los taninos de la tara ya se usan para la fabricación de cueros desde épocas remotas y

sus propiedades están reconocidas, la sección experimental de este trabajo se orienta a optimizar

fórmulas innovadoras utilizando la tara como agente de curtido wet-white. Se proponen

fórmulas para artículos finales.

Palabras clave: Tara, taninos, cuero, wet-white, curtición vegetal, sostenibilidad.

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Original is to return to the simplicity of the origin by the new means.

ANTONI GAUDÍ. ARCHITECT.

Plant a tree

WANGARI MAATHAI. PEACE NOBEL PRIZE

Preface

Since pre-Hispanic eras, plants were used for tanning and dyeing the hides and skins from the

animals hunted for food. With the development of the knowledge and the technologies, humans

have researched substances with specific properties to replace those from nature.

Consumers concern today on the impact that the industry is causing to the environment and the

health of the users, as well on social aspects, and claims for a just commerce and tackling

poverty.

The tannins from tara are well known in the leather industry and they are appreciated because

their light color and lightfastness compared with other traditional vegetable tannins. For this

reason, demand of tara increased during the last decades at the time high performance leather

production for automobile upholstery has experienced a growing demand. However, there are

no specific promotions and researches for the use of tara tannins. Its application as tanning agent

remains in the technical departments of the chemical suppliers. Tannery technicians obtain very

little information from their technical product information-sheets that only specify few

recommendations and provide minimum quality values such as concentration of tannins, solids

and humidity.

Therefore, the technical and scientific scope of this thesis is to fulfill the lack of specific

literature and research focused on tara tannins. Also, it aims to provide technical information for

its promotion to leather technicians.

Cæsalpinia spinosa (Molina) Kuntze, commonly known as tara, is a small leguminous tree or

thorny shrub. Tara is cultivated as a source of high value products from its pods as tannins

based on a gallotannin structure used in the leather industry and seeds as gum for food industry.

Having its origin in the Andean Region, pre-Incas civilizations used the fruits of the tree to

produce dyes for textiles and ceramics, tannins for leather and medicines. Known, therefore, as

“Incas green gold”, there is a strategic interest in Peru, Bolivia and Ecuador, supported by

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international organizations for cooperation, to promote productive processes under

environmental sustainability criteria and social benefit.

Beyond the technical and scientific objectives of this research work, the two implicit pillars in

the scope are:

Environment: The study focus on the tannins obtained from the pods of the tara fruits.

Tara is a tree, thus contributes to fix carbon and nitrogen, and, contrary to other

vegetable tannins, production does not depend from other industries or requires

deforestation. Regulations of chemicals, mainly in Europe, recognize the use of non-

hazard substances from natural origin not chemically treated.

Social: It demonstrates that tara tree is suitable for agro forestry and represents a source

of economical activities for Andean Regions by exporting products to the leather

markets. Also, other products from the fruit of tara are very valuable in other industries

as gum for food and industrial applications and polyphenols with properties in

medicine. The research has started as a cooperation work to engage in poverty in rural

areas in Bolivia.

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Content:

Erratum: ........................................................................................................................................................ 2

Abstract: ....................................................................................................................................................... 3

Resumen: ...................................................................................................................................................... 3

Preface .......................................................................................................................................................... 5

Content: ........................................................................................................................................................ 7

Index of tables ............................................................................................................................................ 11

Index of figures .......................................................................................................................................... 13

Index of photos ........................................................................................................................................... 15

Glossary ...................................................................................................................................................... 17

Introduction ................................................................................................................................................ 21

PART ONE ................................................................................................................................................ 25

1. State of the art of Sustainability ......................................................................................................... 25

1.1. General concept of sustainability .................................................................................................... 25

1.2. The tara tree, a sustainable source of tannins .................................................................................. 27

1.2.2. Economic dimension. Profit ......................................................................................................... 29

1.2.3. Social dimension. People ............................................................................................................. 30

2. Description......................................................................................................................................... 31

2.1. Tara: a sustainable forestry resource from the Andean Region ....................................................... 31

2.2. Distribution and habitat ................................................................................................................... 32

2.3. Botanic characteristics .................................................................................................................... 32

2.4. Tara agro forestry. Environment and economical contribution ....................................................... 33

3. Economical and commercial viability of the tara tanning trading ..................................................... 39

3.1. Analysis of the supply chain ........................................................................................................... 39

3.2. Global production ........................................................................................................................... 40

3.3. Expectations for the tara production during the next years ............................................................. 41

3.4. Analysis of tara potential for the leather industry ........................................................................... 43

3.5. European Policy of Chemicals (REACH) ....................................................................................... 46

4. Theoretic fundamentals .......................................................................................................................... 47

4.1. The Tanning science: the collagen chemistry ................................................................................. 47

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4.2. Hydrothermal Stability .................................................................................................................... 51

4.3 Current tanning practices, processes and techniques for leather ...................................................... 53

4.4. Environmental considerations for the leather industry .................................................................... 54

4.5. The vegetable tanning principles..................................................................................................... 54

4.6. Analytical characterization of tara tannins ...................................................................................... 58

4.7. The chemistry of the syntans ........................................................................................................... 60

PART TWO: EXPERIMENTAL ............................................................................................................... 63

5. Objectives of the experimental part ........................................................................................................ 63

6. Characterization of commercial tara powder .......................................................................................... 65

6.1. Analysis summary of commercial tara commercial samples .......................................................... 65

6.1.1. Data variable: pH analytical solution ........................................................................................... 65

6.1.2. Data variable: Tannins (%) .......................................................................................................... 67

6.1.3. Data variable: Non-Tannins (%) .................................................................................................. 68

6.1.4. Data variable: Insolubles (%) ....................................................................................................... 69

6.2. Conclusion characterization of commercial tara powder ................................................................ 70

7. Characterization of tannins from Bolivian tara fruits ............................................................................. 71

7.1. Description of samples .................................................................................................................... 71

7.2. Preparation of the samples: ............................................................................................................. 72

7.3. Composition of the fruits: ............................................................................................................... 72

7.4. Characterization of the tara powder ................................................................................................ 73

8. Pretanning process. Design I: blending with syntans ............................................................................. 81

8.1. Products, materials and equipment. Design I .................................................................................. 81

8.2. Process and tests. Design I. ............................................................................................................. 83

8.3. Table of tests results and discussions. Design I. ............................................................................. 88

8.4. Conclusions of the Experimental Design I ...................................................................................... 96

9. Pretanning process with tara. Experimental design II: Optimizing with naphthalene sulphonic syntan. 99

9.1. Products, materials and equipment. Experimental design II. .......................................................... 99

9.2. Tests to optimize ratios with naphthalene sulphonic syntan. Experimental design II. .................. 100

9.3. Test results and discussion. Experimental design II: ..................................................................... 104

9.4 Conclusions of the Experimental Design II ................................................................................... 113

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10. Pretanning process with tara. Experimental design III: Optimizing pre-tanning pelt and final pH

conditions. ................................................................................................................................................ 117

10.1. Tests to optimize pretanning process. Design III. ....................................................................... 117

10.2. Test results and discussions. Experimental design III: ................................................................ 119

10.2.1 % NaCOOH vs. initial wet-white process pH ........................................................................... 120

10.2.2 % NaCOOH and % HCOOH vs. final wet-white process pH ................................................... 122

10.3 Results and discussions. Experimental design III ...................................................................... 125

10.4 Conclusions of the Experimental Design III: ............................................................................... 133

11. Thesis practical validation: Manufacturing a sustainable automobile-interior leather article. ........... 137

12. Final conclusions ................................................................................................................................ 143

13. Recommendations for new researches................................................................................................ 147

14. Bibliography ....................................................................................................................................... 149

15. Acknowledgements ............................................................................................................................ 151

ANNEXES ............................................................................................................................................... 153

Annex 1: Botanic characteristics of Caesalpinia spinosa ......................................................................... 155

Annex 2: General chart of integrated tara fruit industrialization .............................................................. 159

Annex 3: Pretanning-retanning recipe for leather car upholstery ............................................................. 161

Annex 4: Tara fruit supply chain. ............................................................................................................. 163

Annex 5: Tara production in Peru, Bolivia and Equador ......................................................................... 167

Annex 6. International leather production. Figures and statistics ............................................................. 171

Annex 7. General overview of making leather from raw hides ................................................................ 187

Annex 8: Environmental considerations for the leather industry ............................................................. 193

Annex 9: The application of the vegetable tannins in the leather industry ............................................... 197

Annex 10: Equipment for experimental tests ........................................................................................... 199

Annex 11: I am a tree and you too ............................................................................................................ 201

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Index of tables

Table 1: Tara forestry: a sustainable source of high value products ........................................................... 34

Table 2: Tara fruit processes ...................................................................................................................... 35

Table 3: General specifications for commercial tara powder ..................................................................... 36

Table 4: Tara exports statistics. Peru. ......................................................................................................... 40

Table 5: Estimated tara production. Period 2011-2012 .............................................................................. 42

Table 6: Objective of tara production in 2015 ....................................................................................... 42

Table 7: 2007 world leather use by end products (Source ICT) ................................................................. 43

Table 8 : Analysis for tara potential for the leather industry ...................................................................... 45

Table 9: Type I collagen: content of amino acids. Source: Dr. G. Reich ................................................... 48

Table 10: The potential reactions on collagen during leather making ........................................................ 49

Table 11: Effects of chemical modifications on shrinking temperature ..................................................... 52

Table 12: Process steps for the production of leather from raw hides. Source: BREF ............................... 53

Table 13: Characterization of 4 commercial samples of tara powder......................................................... 65

Table 14: Analysis summary for pH (commercial samples) ...................................................................... 66

Table 15: Normal distribution for pH ......................................................................................................... 66

Table 16: Analysis summary for tannins (%) ............................................................................................. 67

Table 17: Normal distribution for tannins (%) ........................................................................................... 67

Table 18: Analysis summary for Non-tannins (%) (commercial samples) ................................................ 68

Table 19: Normal distribution for Non-tannins (%) ................................................................................... 68

Table 20: Analysis symmary for Non-tannins (%) (commercial samples) ................................................. 69

Table 21: Normal distribution for insolubles (%) ....................................................................................... 70

Table 22: Reference values of tara characterization ................................................................................... 70

Table 23: Humidity content of tara fruits ................................................................................................... 71

Table 24: Composition of the fruits ............................................................................................................ 72

Table 25: Chemical characterization of tara powder from Bolivian samples ............................................. 73

Table 26: soluble / insoluble matter content in dry conditions ................................................................... 73

Table 27: Tannin / non tannin content of tara powder ................................................................................ 74

Table 28: Content of Gallic acid in tara powder samples ........................................................................... 76

Table 29: Results of hydrolysis test of commercial tara powder ................................................................ 78

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Table 30: Deliming, bating and pickling .................................................................................................... 83

Table 31: Simplex with centroids design ................................................................................................... 85

Table 32: Table o test results. Simplex design with centroids. Experimental design I ............................... 88

Table 33: Recipe for pretanning. Experimental design II ......................................................................... 100

Table 34: Quadratic, centralized, rotatable and orthogonal design for tara and naphthalene sulphonic

syntan. Codification table. Experimental design II................................................................................... 102

Table 35: Test results from experimental design II .................................................................................. 103

Table 36: Conclusions effects of tara and syntan on wet-white properties .............................................. 114

Table 37: Optimal values syntan and tara ................................................................................................ 114

Table 38: Application formula for wet-white. Experimental design III ................................................... 117

Table 39: Variables for Experimental design III ...................................................................................... 117

Table 40 Quadratic, centralized, rotatable and orthogonal design for % sodium formate and % formic acid

85%. Codification table. Experimental design III .................................................................................... 119

Table 41: pH vs % NaCOOH. Experimental design III. .......................................................................... 120

Table 42: Fitted model for pH vs. NaCOOH. Experimental design III .................................................... 121

Table 43: % NaCOOH and %HCOOH vs. final pH. Experimental design III. ........................................ 122

Table 44: Test results from experimental design III ................................................................................. 125

Table 45: Optimal values for each variable. Experimental Design III ..................................................... 133

Table 46: Final recipe for wet-white with tara tannins ............................................................................. 135

Table 47: Quality test results. Car-interior leather from pretanning with tara tannins. ............................ 140

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Index of figures

Figure 1: Three Pillars of Sustainability according to A. Savitz ................................................................ 27

Figure 2: The three dimensions of sustainability for the tara sourcing of tannins ...................................... 30

Figure 3: Production chart flow of tara powder .......................................................................................... 35

Figure 4: Tannic or Gallotannic acid .......................................................................................................... 37

Figure 5: Processes of tara fruit .................................................................................................................. 38

Figure 6: supply chain of tara products ...................................................................................................... 39

Figure 7: Development of tara exports from Peru comparing value and volume ....................................... 41

Figure 8: Tara exports in Peru. Increases of FOB value and volume ........................................................ 41

Figure 9: 2007 world leather use by end products ................................................................................. 43

Figure 10: Diagram of the nature of leather formation by which "leatherlike drying out" is ensured by the

crosslinking and distance-enhancing action of the tannin agents. Source Dr. G. Reich ............................. 49

Figure 11: Gallic acid ................................................................................................................................. 54

Figure 12: Hydrolysable gallotannins and ellagitannins ............................................................................. 56

Figure 13: Fixation curve of the vegetable tannins..................................................................................... 57

Figure 14: Constituents of tara tannins ....................................................................................................... 59

Figure 15: Galloylated quinic acid and structure of tara tannin.................................................................. 59

Figure 16: Phenol sulphonation .................................................................................................................. 60

Figure 17: Condensation of phenol sulphonic acid .................................................................................... 61

Figure 18: Naphthalene sulphonic acid ...................................................................................................... 61

Figure 19: Bar chart of soluble and insoluble matter of tara powder ......................................................... 74

Figure 20: Tannin /non tannin content of tara powder ............................................................................... 74

Figure 21: Calibration curve of Gallic acid for HPLC ............................................................................... 75

Figure 22: Determination of free Gallic acid of a commercial tara powder by HPLC ............................... 76

Figure 23: Chromatography of tara powder from Bolivian fruits. Red arrow indicates the content of gallic

acid. ............................................................................................................................................................ 77

Figure 24: Plot of fitted model for gallic acid and Non Tannin .................................................................. 78

Figure 25: Chromatogram of hydrolyzed tara powder ............................................................................... 79

Figure 26: Plot of fitted model for free Gallic acid and temperature .......................................................... 80

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Figure 27: Sampling hides for testing ......................................................................................................... 82

Figure 28: Coordinate axis for a mixture of three ingredients .................................................................... 84

Figure 29: Estimated response surface for shrinking temperature. Experimental design I ......................... 89

Figure 30: Estimated response surface for tensile strength. Experimental design I ................................... 91

Figure 31: Estimated response surface for tensile elongation. Experimental design I ............................... 93

Figure 32: Estimated response surface for tensile elongation. Experimental design I ............................... 94

Figure 33: Estimated response surface for lightfastness. Experimental design I ........................................ 96

Figure 34: Sampling hides for testing. Experimental design II .................................................................. 99

Figure 35: Quadratic, centralized, orthogonal and rotatable design ......................................................... 101

Figure 36: Pareto chart for shrinking temperature. Experimental design II ............................................. 105

Figure 37: Lineal correlation ST and % syntan. Experimental design II. ................................................. 105

Figure 38: Estimated Response Surface for shrinking temperature. Experimental design II ................... 106

Figure 39: Pareto chart for tensile strength. Experimental desing II ........................................................ 107

Figure 40: Estimated response surface for Tensile. Experimental design II............................................. 108

Figure 41: Pareto chart for tensile elongation. Experimental design II .................................................... 109

Figure 42: Estimated response surface for tensile elongation. Experimental design II ............................ 109

Figure 43: Pareto chart for tear load. Experimental design II ................................................................... 110

Figure 44: Estimated response surface for tear load. Experimental design II .......................................... 111

Figure 45: Pareto chart for lightfastness. Experimental design II ............................................................ 112

Figure 46: Linea correlation lightfastness and % tara. Experimental design II ........................................ 112

Figure 47: Standardized Pareto Chart for Final pH. Experimental design III .......................................... 123

Figure 48: Estimated response surface Final pH vs. %NaCOOH and HCOOH ....................................... 123

Figure 49: Pareto Chart for shrinking temperature. Experimental design III. .......................................... 126

Figure 50: Estimated response surface for ST. Experimental design III .................................................. 126

Figure 51: Standardized Pareto Chart for Tensile. Experimental design III. ............................................ 128

Figure 52: Tensile strength estimated response surface. Experimental design III. ................................... 128

Figure 53: Standardized Pareto chart for Elongation. Experimental design III ........................................ 130

Figure 54: Elongation response surface. Experimental design III ............................................................ 130

Figure 55: Standardized Pareto chart for tear load. Experimental design III............................................ 132

Figure 56: Tear load estimated response surface. Experimental design III .............................................. 132

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Index of photos

Photo 1: Caesalpinia spinosa. Tree, flowers and pods. ............................................................................... 31

Photo 2: Samples of tara fruit collected in Bolivia ..................................................................................... 71

Photo 3: Components of the tara fruit samples from Bolivia (seeds, fibers and powder). ......................... 72

Photo 4: Design of a pretanning process with tara. Experimental Design I ............................................... 87

Photo 5. Light fastness tests. Experimental Design I. ................................................................................ 87

Photo 6: SEM photo. Tara. 24x & 202x ..................................................................................................... 97

Photo 7: SEM photo. Tara + Naphthalene sulphonic syntan. 24x & 202x ................................................. 97

Photo 8: SEM photo. Tara + phenol condensation syntan. 24x & 202x ..................................................... 98

Photo 9: SEM photo. Tara + Naphth. sulphonic syntan + phenol condensation syntan. 24x & 202x ........ 98

Photo 10: Optimization for a pretanning process with tara. Experimental design II. ............................... 103

Photo 11: Light fastness test. Experimental design II .............................................................................. 104

Photo 12: Optimizing for a pretanning process with tara. Experimental design III. ................................ 119

Photo 13: Exhaustion baths I. Experimental design III. ........................................................................... 124

Photo 14: Exhaustion baths II. Experimental design III. .......................................................................... 124

Photo 15: Car-interior leather from pretanning with tara tannins. ............................................................ 140

Photo 16: Blue scale for lightfastness ....................................................................................................... 141

Photo 17: Caesalpinia spinosa (tara): the tree. .......................................................................................... 155

Photo 18: Caesalpinia spininosa (tara): leaves. ........................................................................................ 156

Photo 19: Caesalpinia spinona (tara): flowers .......................................................................................... 156

Photo 20: Caesalpinia spinosa (tara): the fruit .......................................................................................... 156

Photo 21: Tara agro forestry exploitation in Peru..................................................................................... 157

Photo 22: Automobile car interior. Auto leather upholstery..................................................................... 162

Photo 23: Young tara forestry. Cochabamba. Bolivia .............................................................................. 163

Photo 24: Collectors and wholesales dealing with tara pods .................................................................... 164

Photo 25: Tara powder mill. El Callao. Peru ............................................................................................ 165

Photo 26: Fave drums, stainless steel, 500x2mm (DxL). ......................................................................... 199

Photo 27: Simplex drums, stainless steel, 4 T.D.F. .................................................................................. 199

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Glossary

Term Definition

Agro forestry Integrated approach of using the interactive benefits from

combining trees and shrubs with crops and/or livestock. It

combines agricultural and forestry technologies to create more

diverse, productive, profitable, healthy and sustainable land-use

systems

Auxiliary syntan A synthetic tannin not suitable for use alone as a tanning agent,

but designed for use with vegetable tannins to assist tannage,

e.g. to accelerate penetration, or to improve the leather, e.g. its

color and fastness.

Beamhouse The section of the tannery where hide and skins are prepared

for tanning.

Caesalpinia spinosa Scientific denomination for tara tree

Chrome tanned leather Any leather article tanned mainly with chromium salts (usually

chromium sulphate). Near 80% of commercialized leather is

chrome leather.

Collagen The protein composing the white fibers of vertebrate

connective tissue, e.g. dermis of skin.

Corium A kind of connective tissue forming the inner or the two layers

of the skin of vertebrates, which is isolated for conversion into

leather. Built-up essentially of collagen fibers, interspersed

with small amounts of elastin and reticulin fibers, and with

various kinds of cells.

Double-face Clothing or glove leather from wool sheep skins, usable in both

sides or reversible, one having a finished nap, the other the

wool that has not been removed during the beamhouse

operations.

Elongation (stretch) A measure of the stress needed to produce a certain increase in

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resistance the length of a body

FOB International Commercial Term (Incoterm) from the Internation

Chamber of Commerce, used for international commercial

transactions, that stands for “Free On Board” and means that

shipment and loading costs are not included in the selling price.

Grain The surface of a hide or skin exposed by removal of the hair or

wool and epidermis.

Grain tightening The increase of the tightness or firmness of the grain of a

leather, e.g. by application of a high molecular compound.

Hide The outer covering of a mature, or fully grown, animal of the

larger kind.

Horse up, to To place a hide or skin in process over the bar of a special

stand, or horse, to drain or/and age

International

standardization body

Any organization whose primary activities are developing,

coordinating, promulgating, revising, amending, reissuing,

interpreting, or otherwise maintaining standards that address

the interests of a wide base of users outside the standard-

developing organization.

Isoelectric point pH at which a particular molecule or surface carries no net

electrical charge.

Light fastness Ability to endure long exposure to normal light conditions

without serious deterioration of properties, especially color.

Lining A layer of leather, fabric or other material applied to the inside

of a shoe upper, garment, glove, handbag, etc.

Nappa A soft, full-grain, smooth finish, through-dyed, gloving or

clothing leather, made from unsplit sheep, lamb, goat or kid

skins or split cattle hide. Formerly tawed and vegetable, or

chrome, retanned, but now usually full chrome tanned. Also

made from side leather for footwear and leather goods.

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Syntan Molecules obtained by organic synthesis with specific

properties similar to the vegetable tannins

Tannin A type of biomolecule. It is an astringent, bitter plant

polyphenolic compound that either binds and precipitates or

shrinks proteins and various other organic compounds

including amino acids and alkaloids.

Tear resistance Ability of a sheet of material, e.g. leather, to resist a shearing,

or tearing, force applied merely by shearing one area across a

second adjacent, firmly-held, area as in the tongue-tear test.

Tensile strength The tensile force required to break, or rupture, a material,

expressed as newtons (N) of cross section. (kg*m/s2).

Replacement syntan A synthetic tanning agent which can largely, or entirely,

replace the vegetable tannins without fundamentally altering

the tannin process or the character of the finished leather.

Samming Bringing leather to uniformly partly- dry state necessary for

certain finishing operations, e.g. by partially drying-out, by

passing it through the sammying machine or by pressing.

Shrinking temperature The temperature at which a skin or leather decreases in

dimensions when heated under special conditions, e.g. when

heated in water fibers shrunk..

Skin The more or less thick, tough, flexible covering of human and

other animal bodies

Suede A generic term for leathers whose wearing surface, either the

grain or the flesh side, has been finished to have a more or less

fine, velvet-like nap.

Sustainability To meet the needs of the present generation without

compromising the ability of future generations to meet their our

needs.

Syntan An abbreviation of the term synthetic tannin.

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Vegetable tannin A tanning agent contained in, and obtained by extraction of, the

barks, fruits, galls, leaves, roots or wood of certain plants

Wet blue Term for a hide, or skin, which has been subjected to the usual

beamhouse processes, chrome-tanned and left wet; may be

stored or exported in this state.

Wet white Term for a hide, or skin, which has been subjected to the usual

beamhouse processes, chrome free and left wet, may be stored

or exported in this state.

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Introduction

The role of the tanning science is probably the key of the success for a dynamic and innovative

business supplying a noble and natural material to the chain of consumer goods that include

shoe, upholstery, apparel, car interiors, bags, travel suitcases, flexible gadgets for tools and

machinery and many other applications. Being one of the oldest industries since humans live on

the Earth, leather activities are driven by commercial indicators, but technology has been always

the essential support to allow creating new markets and fulfilling the performing requirements

and rigorous demands from consumers.

The leather industry is the solution to the disposal for a waste of the meat industry and

transforms hides and skins from slaughterhouses into a high value material. Nevertheless,

tanning is a potentially pollution-intensive activity. The environment effects that have to be

taken into account comprise not merely the loan and concentration of the classic pollutants, but

also the use of certain chemicals.

This thesis aims to validate the compliance of the two hypotheses already implicit in the title of

the work. The fruit of the tara tree is proposed as a source of sustainable tannins. Thus,

experiments are designed to prove that the application of such tannins, well known since remote

eras, can respond as newest technologies of tanning leather that comply quality article standards

at the time to meet the highest exigencies of chemical auxiliaries used in the consumer goods

supply chains.

Concepts on sustainability from recent forums and expert publications are appraised in Section

1 and the model based on the Triple Bottom Line of social, economic and environmental

dimension is chosen to support the first hypothesis. Section 2 and related annexes describe tara

tree taxonomy and the contribution of its agro-forestry to the environment as a renewable source

of active substances to be economically exploited in industries such tanning, food,

pharmaceutical and other business while improving quality life for remote rural Andean

communities. Section 3 analyses the supply chain of tara fruit components and their derivates,

production and market, and concludes that opportunities depend on availability and price

consistency. Thus, tara agro-forestry should replace the current practices of harvesting tara wild

trees. The section concludes that tara products, if they are not chemically treated, are exempt of

costly safety tests and registrations according to European Regulations such the REACH.

The hypothesis of tara pre-tanning process as innovative technology in the leather making is

proven with the analysis of the performance of the pelts submitted to the treatment with tara,

blended with general synthetic tannin groups, at different ratios and application conditions.

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Section 4 reports the theoretical scientific fundamentals to be considered to design and

understand the results of the Experimental Part, based mainly on literature from classic works

among well known researchers highly recognized by the leather technician community. The

collagen, Type I, is the constituent of the hides and skins. This protein consists in a fibril net of

chains of amino acids, mainly glycine, proline and hydroxyproline. The tanning process consists

on the stabilization of collagen through the bonding of the amino acid functional groups and the

tanning agents to avoid the phenomena of parchment. Hydrothermal stability is used as the main

indicator to control the degree of tanning. General current tanning practices are briefly

described and chemistry of vegetable tannins and synthetic tanning agents as well as analytical

characterization are summarized at the end of this section.

Section 5 introduces de main goals of the experimental designs to prove the second hypothesis

of innovation. Section 6 analysis commercial tara powder from different leather chemical

suppliers by means of content of water, soluble and insoluble matter, tannins, non-tannins and

pH analytical solution. Limits of these parameters are statistically established within the normal

distribution. These limits are useful for comparing, in section 7, further characterizations of tara

powder processed in the laboratory from fruits obtained in different regions of Bolivia. This

section concludes that, despite the natural origin of tara powder, composition of ingredients

maintain consistent ratios. This section analyzes the correlation of non-tannins content and the

Gallic acid hydrolyzed from tannin molecule. In this case, the null hypothesis cannot be rejected

and such correlation cannot be proven, while a hydrolysis of Gallic acid is explained after the

treatment of tara powder exposed to time and temperature.

Section 8, 9 and 10 statistically analyze the results of the experiments designed with the support

of the Statgraphics Plus software, version 5.0 from Statpoint Technologies, Inc (Warrenton, VA,

USA). In all cases, the considered dependent variables are the shrinkage temperature, the

measurement of the tensile strength and elongation and the measurement of the tear load. All

these physical properties are common required for most of the leather article quality

specifications.

Blending tara powder with syntan for pretanning process, section 8, is designed with a Simplex

with centroids method. Tara powder with naphthalene sulphonic syntan is found as the most

suitable for tara tanning acting as a dispersant and aiding tannins to go through the inner layer of

the pelt.

Section 9 optimizes the blend composition ratios of tara powder and naphthalene sulphonic

syntan. Design II is based on quadratic, orthogonal, centralized and rotatable model to analyze

best fitted variable response surface. The mean of the optimal values is calculated to obtain the

ratio of 12% of tara powder and 7 % of naphthalene sulphonic syntan.

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This composition is then applied under certain conditions, by means pH measurement previous

and after pretanning operation, Section 10. Design III is also based on quadratic orthogonal,

centralized and rotatable model to analyze best fitted variable response surface and the mean of

optimal values of sodium formate and formic acid, as pH regulator agents, are calculated

obtaining initial pH of 5,23 and final pH of 3,64.

Section 11 describes the manufacturing of an automobile-interior leather article from wet-white

processed with tara, at pilot scale and according the results of the experiments. The leather is

treated later with a regular recipe of retanning, fatliquoring, dyeing, mechanical operations and

finished by coating. The leather article is tested for physical properties according the ISO

standards of article specification and the results demonstrate the feasibility of the pretanning

with tara as a sustainable and innovative source of tannins that can meet the quality leather

requirements for consumer goods.

The research work was initially supported by the funding project:

“Aprofitament sustenible de la tara, per la generació i diversificació de rendes en el

medi rural bolivià”, Consorci de promoció Comercial de Catalunya, COPCA,

Generalitat de Catalunya, Programa de cooperación pel desenvolupament. Referencia

53695/2008.

Results of this research are included in the:

project labeled E! 6565, “Low carbon products to design leather processes based on

Sustainable Tannins to improve leather manufacture, LOWEST” supported by the

EUROSTARTS program powdered by EUREKA R&D platform Organization and the

European Community.

During the execution of the research, partial results have been published in indexed scientific

journals or national and international congresses:

“Optimizing a Sustainable and Innovative Wet-White Process with Tara Tannins”

presented at the 107th Annual Meeting of the American Leather Chemists Association,

June 9 - 12, 2011, Treasure Islane Resort, Red Wing, MN. Published in Journal of the

American Leather Chemist Association (JALCA), Vol 106, 2011, pages 278- 286.

Authors: J.C. Castell, C. Fabregat, S. Sorolla, D. Solano, Ll. Ollé, A. Bacardit.

“Tara (Caesalpinia spinosa): The sustainable source of tannins for innovative tanning

processes”. XXXI IULTCS Congress. Valencia, September 2011. Authors: J.C. Castell,

S. Sorolla, M. Jorba, J. Aribau, Ll. Ollé, A. Bacardit. Publication is foreseen in JALCA.

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“Antioxidant activity of tara pods” VI National Congress of Food Science and

Technology. Valencia, 8-10 June, 201. Authors M. Skowyra, M. Davila, C. Fabregat,

J.C. Castell, M.P. Almajano.

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PART ONE

1. State of the art of Sustainability

1.1. General concept of sustainability

Sustainability is a widely-used term and is gaining attention in many parts of society, including

government, business, academia, and in the public. However, it is hardly an agreed-upon

concept. Even, among scientists there are numerous definitions.

Many people interpret it in the sense of continuous growth and the idea of sustainability focuses

on depletion of resources. Others consider that sustainability covers also irreversible pollution,

conservation of nature and other environmental an ecological aspects. Some also include the

aspects of quality of human life.

Therefore, to be able to support a sustainable way of living in our planet, a clear definition of

sustainability is required.

The word sustainability is derived from the Latin sustinere (tenere, to hold). Dictionaries

provide more than ten meaning for sustain: “maintain”, “support”, “endure”…

Gro Harlem Brundtland, physician, former Prime Minister of Norway and international leader

in sustainable development and public health, analyzed in 1987 the world situation

demonstrating that the consequences of the development of the humanity were the

environmental degradation, the increase of poverty and vulnerability of certain societies.

She introduced for the first time the term of sustainability or sustainable development as

“development that meets the needs of the present without compromising the ability of future

generations to meet their own needs”1.

Much of the contemporary discussion over sustainability starts from the ideas of resource

scarcity and the transformation of the planet by humanity, emphasized by rapid population

growth and industrialization.

Critical natural capital assets provide humans with goods and services that cannot be replaced,

reproduced or substituted. Sustainability implies that there are limits that must be respected and

these assets shall always be respected.

Another perspective is characterized by dynamic systems that maintain themselves overtime

compromising three elements:

1 U.N. Documents. Report of the World Commission on Environment and Development: Our Common Future. Chapter II: Towards Sustainable Development. UN Documents: Gathering a Body of Global Agreements has been compiled by

the NGO Committee on Education of the Conference of NGOs from United Nations web sites

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Depletion of resources, in order not to leave future generations empty-handed

Environmental and ecological aspects, in order to enable present and future generations

to live in a healthy environment, in harmony with nature

Quality of life, in order to ensure human well-being for present and future generations.

Economy is not explicit included, though politicians often use the term “sustainable economy”.

During the last decade of the Twentieth Century, a lot of academic debates on concepts and

definitions were taken about Corporate Sustainability (CS) and Corporate Social Responsibility

(CSR). “In academic debates and business environments hundreds of concepts and definitions

have been proposed referring to a more humane, more ethical, more transparent way of doing

business”2. Marcel Van Marrewijk and Marco Werre, based on historical perspectives,

philosophical analysis, impact on changing contexts and situations and practical considerations

concluded on abandoning a “one-solution-fits-all” definition 3.

According to the US National Research Council, sustainability is “the level of human

consumption and activity, which can continue into the foreseeable future, so that the systems

those provide goods and services to the humans, persists indefinitely”.

Professor Robert N. Stavins4, included other concepts like dynamic efficiency consisting on

accounting for intergenerational equity or total welfare, representing the consumption of market

and non-market goods and services.

The concept of Sustainability has become a common goal for many national and international

organizations including industry, governments, NGOs and universities.

This research work justifies the concept of Sustainability based on the Triple Botton Line

(TBL), from Professor Andrew W. Savitz5. For businesses, sustainability is a powerful and

defining idea: a sustainable corporation is one that creates profit for its shareholders while

protecting the environment and improving the lives of those with whom it interacts. It operates

so that its business interests and the interests of the environment and society intersect. A

sustainable business stands an excellent chance of being more successful tomorrow than it is

2 Marcel van Marrwijk, Concepts and Definitions of CSR and Corporate Sustainability: Between Agency and Communion.

Journal of Business Ethics, 44, 95-105, 2003. Netherlands.

3 Marcel van Marrwijk and Marco Werre, Multiple Levels of Corporate Sustainability.

http://www.vanmarrewijk.nl/pdf/021206131353.pdf. September 2002 4 Robert N. Stavins, Post-Kioto International Climate Policy. Summary for policymarkets. Research for the Harvard

Project on International Climate Agreement. Cambridge. MA. USA. 2009. ISBN:9780521138000 5 Andrew W. Savits. The Triple Botton Line. Business/Management. Wiley. CA. 2006. ISBN-10: 0787979074 | ISBN-

13: 978-0787979072

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today, and remaining successful, not just for months or even years, but for decades or

generations.

Increasingly, businesses are expected to find ways to be part of the solution to the world’s

environmental and social problems. The best companies are finding ways to turn this

responsibility into opportunity. We believe that when business and societal interests overlap,

everyone wins.

Thus, TBL objectives approach economic (profit), environmental (planet) and social (people)

terms: “The triple bottom line (abbreviated as TBL or 3BL, and also known as people, planet,

profit or the three pillars) captures an expanded spectrum of values and criteria for measuring

organizational (and societal) success: economic, ecological and social. With the ratification of

the United Nations and ICLEI6 TBL standard for urban and community accounting in early

2007, this became the dominant approach to public sector full cost accounting. Similar UN

standards apply to natural capital and human capital measurement to assist in measurements

required by TBL, e.g. the ecoBudget standard for reporting ecological footprint.”7. (Figure 1):

Figure 1: Three Pillars of Sustainability according to A. Savitz

1.2. The tara tree, a sustainable source of tannins

1.2.1 Environmental dimension. Planet

The environmental (planet) dimension of sustainability denominates those terms that describe

environmental performance in order to minimize the use of hazardous or toxic substances,

resources and energy.

6 International council for local Environmental initiatives (ICLEI) founded in 1990, is an association of over 1220 local

government Members who are committed to sustainable development See web page www.iclei.org

7 http://en.wikipedia.org/wiki/Triple_bottom_line. Date of consultancy March, 15th, 2010

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These terms, arranged from preventive to control principles, are:

renewable resources

resource minimization

source reduction

recycling

reuse

repair

regeneration

recovery

remanufacturing

purification

end-of-pipe

degradation

Environment dimension on this research refers mainly to the renewable supply of the tara.

Renewable resources are available in a continually renewing manner, supplying materials and

energy in more or less continuous ways. Renewable resources do not rely on fossil fuels of

which there are finite stocks.

The term emerges as a response to increased carbon dioxide emissions. The research focus on

the tannins obtained from the pods of the tara fruits. Tara is a tree, thus contributes to fix carbon

and nitrogen, and, contrary to other vegetable tannins, production does not depend from other

industries or requires deforestation. Regulations of chemicals, mainly in Europe, recognize the

use of non-hazard substances from natural origin not chemically treated.

Minimization of resource usage is understood as conservation of natural resources. It is an

activity that can be applied to any reduction of usage of resources. Therefore, the term

encompasses not only raw materials, water and energy, but also applies to natural resources

such as forestry, watersheds, other habitats, hunting, fishing, etc. All these resources and

processes which enable ecosystems to survive and are essential for helping societies to make

progress toward sustainability must be addressed. Thus, resources can be conserved, their

availability improved and maintained. Reduction in the usage of materials and energy, such as

tanning mineral salts, syntans and some other vegetable extracts, can result in dramatic cost

savings.

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1.2.2. Economic dimension. Profit

The economic dimension of sustainability includes terms like Environmental Accounting, Eco-

efficiency and Ethical Investments8.

Environmental accounting is designed to bring environmental costs to the attention of the

corporate stakeholders who may be able and motivated to identify ways of reducing or avoiding

those costs while at the same tame improving environmental quality and profitability of the

organization. Environmental accounting can be applied at the national, regional and corporate

levels. National accounting refers to physical and monetary accounts for environmental assets

and the costs of their depletion and degradation. Corporate environmental accounting refers to

environmental auditing, but may also include the costing of environmental impacts caused by

the corporation.

The term of eco-efficiency was perceived within numerous definitions of cleaner production.

Eco-efficiency is the delivery of competitively priced goods and services that satisfy human

needs and bring quality of life, while progressively reducing ecological impacts and resource

intensity throughout the life cycle, to a level at least in line with the earth’s estimated carrying

capacity. It is based on the concept of “doing more with less” representing the ratio between

economy and environment, with the environment in the denominator. It is about efficient use of

materials and energy in order to provide profitability and the creation of added value.

Ethical investments or socially responsible investments are financial instruments (mortgages,

bank accounts, investments, utilities and pensions) favoring environmentally responsible

corporate practices and those, supporting diversity as well as increasing product safety and

quality.

In the scope of this research work is a demonstration of the economical viability of agro forestry

as a new trading of supplying tannins for the tanning industry, stabilizing production and prices

to satisfy an increasing demand concerning the impact of the industry to the environment, the

security of the employees in the tanneries and the health end users of leather articles. This is

enhanced with regulations like the European REACH or restrictions from international

companies as alternative to other chemicals substances that shall comply complex and costly

registrations.

8 Glavic, Peter, Lukman Rebeka, University of Maribor, Demartment of Chemistry and Chemical Engineering, Slovenia.

Review of Sustainability terms and their definitions. Journal of Cleaner production. 15 (2007). 1875-1885.

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1.2.3. Social dimension. People

Social dimension of sustainability is composed of terms such Social Responsibility, health and

safety. “polluter pays” principle (taxation) and reporting to the stakeholders.

Social responsibility refers to safe, respectful, liberal, equitable and equal human development,

contributing to humanity and the environment. Furthermore, the term health and safety usually

refers to the working environment and includes responsibilities and standards.

Tara tree is suitable for agro forestry and represents a source of economical activities for

Andean Regions by exporting products to supply leather markets. Also, other products from the

fruit of tara are very valuable in other industries as gum for food and industrial applications and

polyphenol source with properties in medicine.

The research started as a cooperation work to engage in poverty in rural areas in Bolivia.

Figure 2: The three dimensions of sustainability for the tara sourcing of tannins

Economic

(profit)

Social

(people)

Environment

(planet)

Forestry

Fruit

Social: Economic alternatives

for rural areas in Bolivia, Peru and

Ecuador

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2. Description

2.1. Tara: a sustainable forestry resource from the Andean Region

Cæsalpinia spinosa (Molina) Kuntze, commonly known as tara9, is a small leguminous tree or

thorny shrub. Tara is cultivated as a source of high value products from its pods and seeds as

tannins based on a galloylated quinic acid structure, used in the leather industry, and gum for

food industry. It is also grown as an ornamental plant because of its large colorful flowers and

pods.

Photo 1: Caesalpinia spinosa. Tree, flowers and pods.

Having its origin in the Andean Region, pre-Incas civilizations used the fruits of the tree to

produce dyes for textiles and ceramics, tannins for leather and medicines. Known, therefore, as

“Incas green gold”, there is a strategic interest in Peru, Bolivia and Ecuador, supported by

international organizations for cooperation, to promote productive processes under

environmental sustainability criteria and social benefit.

The tara name comes from Aimara language and means flat because the shape of the pods.

Cesar Barriga10

resumes this specie as:

Plastic: it is able to adapt to several climates and soils

Rustic: it is not exigent and can grow in superficial, acid and low fertility soils

Multiple uses: the fruit is profitable, fixes the nitrogen, produces pollen and nectar, and

can grow in agro-forestry systems together with other crops.

9 Known names (Jones, 1987 and De la Cruz (2004): “Tara”, “Taya” (Peru), “Guarango” (Ecuador), “Cuica”, “Serrano”, “Vinillo”, “Acacia Amarilla” (Yellow acacia), “Andean Dividivi”

Synonyms: Caesalpinia victoria (H.B.K.) Bentham ex Reiche; Poinciana spinosa Molina; Caesalpinia pectinata Cavanilles;

Coulteria victoria HBK, Tara Spinosa (Molina) Britt & Rose; Caesalpinia stiulata (Sandwith) J.F.

10 Cesar Barriga: PEBAVI – Peru. Personal interview in June 2010

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Due to its wildness, there exists a variety of plants according the regions and the living

conditions, thus the content of tannins can vary from 30% to 80%. Currently, institutions and

universities carry out researches to characterize the genetic variability11

.

2.2. Distribution and habitat

Cæsalpinia. spinosa can be found growing throughout northern, western and southern South

America, from Venezuela to Argentina, subtropical and semitropical regions between 4º to 20º

South latitudes. It has been introduced in dry parts of Asia, the Middle East and Africa and has

become naturalized in California.

Normally tara grows in areas with a yearly rain of 400 to 1,100 mm, and on sanded or degraded

soils. It is a wild tree, normally isolated, but sometimes, can form small forests. Generally

resistant to most pathogens and pests, it lives between 0 and 3,000 meters above sea level. Trees

begin to produce after 4–5 years. If well irrigated, they can continue to produce for 80 years,

though their highest production is between 15 and 65 years of age.

2.3. Botanic characteristics

Annex 1 describes the Caesalpinia spinosa features.

Taxonomic classification by USDA12

:

Kingdom Plantae Plants

Subkingdom Tracheobionta Vascular plants

Superdivision Spermatohyta Seed plants

Division Magnoliophita Flowering plants

Class Magnoliopsida Dicotyledons

Subclass Rosidae

Order Fabales

Family Fabaceae Pea family

Genus Caesalpinia Nicker

Species Caesalpinia spinosa (Molina) Kuntze Spiny holdback

11 RAPDs (Random Amplifies Polymorphic DNAs) molecular makers is the most common technique to characterize the

genetic variability.

12 United States Department of Agriculture (USDA). Natural Resources Conservation Services. Plants Profile. Caesalpinia Spinosa (Molina) Kuntze. (Date of consultancy December, 13, 2009)

http://www.plants.usda.gov/java/nameSearch

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2.4. Tara agro forestry. Environment and economical contribution

Lorena Mancero13

goes over the contribution (↑) and the risks (↓) to the environment of the

production of tara. Table 1 summarizes them:

Factor of the chain affecting

the environment

How?

Production

Clone method of propagation Risk of lower resistance to blight and

sicknesses ↓

Land selection for forestry

Risk of replacement for native

species ↓

Reforestation of desolated areas to

create economic alternatives

Protection of sloping soils or

degraded ecosystems

Forestry management Strong and healthy trees, growing in

proper areas

Better profit of nutrition, sunlight and

water

Better control of harvest, blights and

sicknesses

Increase of pod production

Replacement of species in natural

forest, affecting fauna populations ↓

Plantation Supplies nitrogen to the soil

Nitrogen associates to other crops

like corns, potatoes, barley or

13 Programa Regional ECOBONA-INTERCOOPERACION. “La Tara (Caesalpinia spinosa) en Perú, Bolivia y Ecuador:

Análisis de la Cadena Productiva en la Región”. Serie Investigación y sistematización. Vol. 02. Quito. 2009. Pag. 33

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sorghum.

Ideal to protect soils erosion, mainly

in arid or semiarid areas

Does not require much water (600

mm rain or 4.000-6.000 m3/ha/year).

Good resistance to large dry seasons

Proper to combine with apiculture

Leaves are good for animal feed

Possibilities as economic alternative

Production of tannins does not need

deforestation

Transforming

Production of tara powder Industrial risk. Needs protection for

employers ↓

Production of tara gum High requirements of control for the

food industry ↑

Consumption

Application of tara powder for

tanneries

As alternative to other tanning

substances, specially chromium

salts, or vegetable tannins from

wood that require deforestation

Application of tara powder in

artisanal tanneries

Water pollution from the tanning

process

Low protection to employers for

manipulating tara power, and low

education of chemical uses.

Table 1: Tara forestry: a sustainable source of high value products

The fruit of tara tree and its derivates have a high interest in a number of industries and, thus, a

great worldwide economical potential for commerce. The properties of pods and seeds result in

a sustainable and quality raw material for several applications.

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The weight of the fruit of tara contains 60-64 % of pods, 34-38 % of seeds and 2 % of non-

valuable residues. Annex 2 shows the industrial flow chart of by-products obtained from tara

fruits. It is important to point out that tara powder contains 45- 50% tannins, and the seeds 24%

tara gum.

Table 2: Tara fruit processes

The pods are threshed and the seed separated. Tara powder is obtained by simply mechanically

milling and sifting the gross powder, as can be seen in figure 3:

Figure 3: Production chart flow of tara powder

The tara powder is a fine (100 to 200 mesh) yellowish sawdust. Further than the leather

industry, it is used, as well, in the chemical industry to obtain tara extract, also used in the

leather industry and to other applications. (Annex 2).

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The leather industry appreciates the tara powder as a source of vegetable tannins to obtain light

colors, with good light fastness, and full and soft leather articles, with a firm and smooth grain.

Tara is easily soluble in water and do not contain color substances like other vegetable tannins.

Tara powder can be used to tan all kind of hides and skins and to re-tan chrome tanned leathers

to improve the grain-tightening. The main application is in the manufacture of leather for car

seats. The general specifications for commercial tara powder for tanning application are14

:

Tannin content min. 48%

Water content max. 13 %

pH (at 6.9ºBè) 3 – 4

Table 3: General specifications for commercial tara powder

Annex 3 shows a typical production recipe to produce car upholstery leather from bovine hides

with a wet white process pretanning with glutaraldehyde.

There are, however, some difficulties of the tara tannin when compared with other vegetable

tannin extracts:

High concentration of insoluble solids (tara powder contain high quantities of cellulosic

compounds from the tara pods if tannins are not extracted properly)

Tanning limits when tara tannin is the single compound for tanning. Hydrolyzing

vegetable tannins cannot increase the shrinking temperature.

Easily produces complexes with iron and other metals and form dark spots on the

leather when is contaminated. Usually tara mills and several machines used during the

leather processing for mechanical operations contain parts made with iron and the risk

of such dark spots is quite high.

To obtain tara extract, the tara powder should be treated at 65-70ºC for 30-40 minutes adding to

the powder 4 to 5 parts of is weight with water and washing the liquor 5 times. Then the liquor

is purified by decantation and filtration, and concentrated from 2-5º Bè to 11-12ºBè. The

powder of tara tannin extract is obtained by atomization.

Tara extract is used to produce tannic acid, and founds valuable applications in the food and

beverage industries, to clarify and give astringency to wine, tea, coffee, cacao, beer and other

food.

14 ORMOTAN© T polvo. SILVATEAM. Silvachimica S.r.l. Via Torre 7. San Michele di Mondovì (CN). Italia. TE: +39.0174.220256. (Date of consultancy September, 15, 2009)

http://www.silvateam.com/index.php?lang=es&id=1,0,2&v2=1

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Recent investigations demonstrate that tara tannin and its derivates have excellent properties as

antioxidant agents to prevent cardiovascular diseases15

. Also, they have astringent properties

with pharmaceutical capacity to avoid irritation and harm by reducing protein coagulation. The

tannic acid is used as hemostatic to cut down hemorrhages and, mostly, for burning treatment.

Figure 4: Tannic or Gallotannic acid

The gallic acid can be obtained by hydrolysis of tannic acid with sulfuric acid. Chemical

hydrolysis is, however, costly and contains impurities, but enzymes, like tannases from bacteria,

can be used. It founds valuable applications in the pharmaceutical industry because has

biological properties as antioxidant, biocide (virus and bacteria) and analgesic, but also, is used

in other industries, e.g. to clarify vegetable fats, beer, or to obtain inks and as analytical

reactive.

The tara gum is obtained by milling the endosperm from the tara seeds, after mechanical

separation of the husk and the germ. The high viscosity of the tara gum is well appreciated in

the food industry and it is an excellent hydrocolloid with good properties as thickener and

stabilizer agent used to prepare ice creams, gelatin, powder and liquid soaps, yogurt, sauces like

mustard, mayonnaise, ketchup; cream and soft cheeses, bakery, meat, among others. It is stable

at pH higher than 3.5, retains water, soluble at cool temperatures, and do not modifies the

savors. Further than the food industry, tara gum has also applications in the pharmaceutical

industry, cosmetics, mining, paper, textile, oil, and others.

15 M. Skowyra, M. dávila, C. fabregat, J.C. Castell, M.P Almajano. Actividad Antioxidante de la vaina de tara. VI

Congreso Nacional de Ciencia y Tecnología de los Alimentos. Valencia, 8-10 June, 2011.

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The germ of tara, obtained from the seed cotyledons, has a high content of proteins and it is sold

for animal feed and, also, to the pharmaceutical and cosmetic industry as a source of proteins.

The germ of tara is also rich in vegetable oils.

Figure 5: Processes of tara fruit

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3. Economical and commercial viability of the tara tanning

trading

3.1. Analysis of the supply chain

The current source of tara is mainly natural forests from the Andean region of South America

where some agro-forestry exploitations are introduced. Peru is the main area for sourcing tara

fruits to obtain tannins followed by far by Bolivia, Chile, Ecuador and Columbia.

The tara supply chain stars from planting the tara tree seeds in agro forestry farms or from

harvesting the fruits from wild trees in natural forests. Much of the tara production consists of

wild collection, thus, a major problem comes from the quality differences between collected tara

and cultivated tara. This thesis compares in Part Two, Experimental, section 6, characterization

of commercial tara powder and section 7, characterization of tannins from Bolivian tara fruits,

commercial and samples collected in different regions of Bolivia.

The actors of the production and supply chain are those that are involved in the trading process,

from farming, harvesting, collecting, transforming and trading the product and the final users.

Annex 4 fully describes the tara supply chain and it is summarized in figure 6.

Figure 6: supply chain of tara products

Currently, the major source of tara pods are wild forests and, only in certain areas, tara pods

come from forestry farmers.

There is a gap between the production of tara and its demand, thus, there are clear opportunities

for forestry farmers to increase production to supply tara powder for the leather industry and

tara gum for the food industry. Industry sources are speaking about a monopoly in the market

for unprocessed tara with one of a few Italian companies dominating the market. As a result of

the undersupply, prices go up. Some processors have, therefore started their own tara

production. However, it takes years before the new tara trees start producing.

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3.2. Global production

Despite tara tree is native from a wide range of countries according to the World Agroforestry

Center16

, approximately 80% of global production takes place in Peru.17

Sources of tara are also

found in Chile, Ecuador and Colombia and other countries like Bolivia, Venezuela, Cuba and

cultivated in China, India, Ethiopia, Kenya and Morocco.

According to Schciaffino18

, production of tara in 2004 was between 115,000 and 138,000 tons

of tara pods, considering that a tree of Cæsalpina spinosa is able to produce 50-150 kg of fruit

per year, and 20-40 kg. of pods.

Annex 5 describes production features in Peru, Bolivia and Equator.

It is calculated that 97% of the production was exported as a tara powder or tara gum, therefore,

we can make some estimation based on export trade data.

Year 2004 2005 2006 2007 2008 2009

FOB Value USD 13,959,936 16,.705,333 20,956,791 31,756,831 41,326,224 25,317,.943

Delta FOB Value

20% 25% 52% 30% -39%

Tons 12,878 15,043 15,005 19,918 17,852 17,828

Delta volum

17% 0% 33% -10% 0%

Price USD/kg 1.08 1.11 1.40 1.59 2.31 1.42

Table 4: Tara exports statistics. Peru.

Table 4 clearly shows how the variability of the market prices has impacted in terms of export

value. Since exports in volume (demand) increased from 2004 to 2006, prices rose from an

average of USD/kg 1,08 to USD/kg 1,40. During the years 2005 to 2007 the market was

consolidated because the highest demand of chrome-free leather for automobile seats.

As production of tara is unable to satisfy the demand, obviously prices go up. This factor is

enhanced when the market is dominated by one company, creating a monopoly in the market.

In 2007, tara powder exports achieved the highest values, probably the full availability of

production, close to 20,000 tons. Export selling prices also increased to USD/kg 2.31 exceeding

16 Agroforestry Database 4.0. World Agroforestry Center. Nairobe. (Date of consultancy October, 24, 2009)

http://www.worldagroforestry.org/treedb2/AFTPDFS/Caesalpinia_spinosa.pdf

17 Tara Casealpina spinosa. Market Survey. Compiled by Swiss Import Promotion Programme (SIPPO) by ProFound –

Advisers In Development 2008/2009.

18 Schiaffino, JC. Estudio de mercado de la tara. Perú Programa Desarrollo Rural Sostenible, GTZ, Universidad del

Pacífico, GOPA. 2004

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expectations of demand. As a consequence, during 2008 the export value increased but volume

production was stabilized to 18,000 tons.

During 2009 the automobile industry, and also the leather industry in general, suffered the

international financial crises and figures were stabilized to volume production of 18,000

tons/year and average price19

around USD/kg 1.50.

For better understanding, Figure 7 compares the trends of the export value in Peru during the

years 2004 to 2009 compared with the progress of the production volume.

Figure 7: Development of tara exports from Peru comparing value and volume

Figure 8 compares the yearly increase of FOB value of the export trade of tara products and the

progress of volume. While the exports in 2007 increased in demand, the market reacted

negatively to the price increase. Prices went down in 2009 and production was stabilized.

Figure 8: Tara exports in Peru. Increases of FOB value and volume

3.3. Expectations for the tara production during the next years

Currently, administrations from the three Andean countries project new forestry developments

of 4,730 ha and future production of tara powder can be estimated according to the table 520

.

19 Average price is the mix price for tara powder and tara gum.

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Region Peru Ecuador Bolivia

Product ha 7,730 7,500 50 180

t harvested pods 115,950 112,500 750 2,700

t available tara powder 71,889 69,750 465 1,675

Table 5: Estimated tara production. Period 2011-2012

The goals of the development of the tara in the region for 2005 is to double this production

figures and exploitation plans are going to be implemented. This is supported with the highest

demand of tara products in the leather industry, but also for other products with high potential

demand, as the gallic acid and vegetable thickeners.

Region Peru Ecuador Bolivia

Production ha 14,000 10,000 2,000 2,000

t harvested pods 210,000 150,000 30,000 30,000

t available tara powder 15,960 11,400 2,280 2,280

Table 6: Objective of tara production in 2015

From the production point of view, there is enough experience for forestry technical assistance

related to forest and forestry management, plagues control and seed selection and reproduction.

There is a demand for Standardization of the technical quality of the products what is under

discussion with International Standardization bodies to coordinate quality requirements

according the final application.

There is no doubt that the interest and demand of tara products is growing at international

levels. However, alternative products are also available, either from other natural species or by

organic synthesis. It is important to develop technologies to improve the present offer of tara

products, by customizing or improving the quality, but at the right costs for the market.

There is an opportunity for the leather industry in order to replace chemicals and to obtain

sustainable process and articles. Tara tannins offer a wide range of advantages if quality and

prices fulfill the expectations of the market.

20 Mancero L., 2008, La Tara (Caesalpinia spinosa) en Perú, Bolivia y Ecuador: Análisis de la Cadena Productiva en la

Región. Programa Regional ECOBONA – INTERCOOPERACIÓN, Quito. Quito, febrero 2009. Page 91

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3.4. Analysis of tara potential for the leather industry

The production of raw hides and skins depends on animal population and slaughter rate and is

related mainly to meet consumption.

The worldwide organization for producers of leather, International Council of Tanners (ICT)21

estimates a global leather production of 22,930 million square feet:

2007 World leather use by end products

million sq. ft % total

Footwear 11.925 52%

Garments 2.290 10%

Auto 2.340 10%

Furniture 3.210 14%

Gloves 1.010 4%

Other leather products 2.155 9%

Total 22.930

Table 7: 2007 world leather use by end products (Source ICT)

More than half of the world leather production is used for the shoe industry either for upper,

sole or lining. While upper leather remains as the most important material for man, women and

children footwear and it is strongly appreciate because of its quality, properties and aspect,

lining has tendencies to be substituted by textile, natural or synthetic materials, and sole is

produced mainly with rubber and other synthetic materials. Sole leather is used for high

standard and classic shoes. Sports shoes for high performances also use upper leather

technically treated with other materials. The main shoe producers markets are China, India and

Brazil with some countries growing during the last years, mainly in South-East Asia, like

Vietnam. Italy continues as a reference for fashionable trends in shoe design and also maintains

an important market share.

Figure 9: 2007 world leather use by end products

21 ICT, Leather Trade House, Kings Park Road, Moulton Park, Northampton, NN3 6JD, UK, (Date of consultancy May,

15, 2010) www.tannerscouncilict.org

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Furniture is the second biggest market for leather where it competes with other materials,

mainly textiles and plastics. Elegancy and comfort are the main drivers among design and

fashion. Italy, Argentina and Brazil are the biggest markets for upholstery, but China also is

growing its production for furniture.

Auto leather has experienced a high increase during the last decades, only interrupted recently

due to the automobile industry crisis, especially in North America. Leather is used to

personalized high standard auto producers and gives comfort and elegancy. Leather competes in

the auto industry with synthetic fabrics.

Auto industry is also very exigent in terms of technical features. Fastness and physical

properties are considered by designers and engineers. Also, the substances contained in the

leather are strictly analyzed and, in many cases, forbidden. Auto manufacturers are very

concerned on social and environmental issues. Comfort and design are key factors for marketing

car interiors while sustainability commitment must be considered as prerequisite.

During the last two decades, some auto manufacturers require new tanning processes avoiding

the traditional chrome tanning or “wet-blue”. Therefore, tanners and the chemical industry have

developed alternative processes using organic tannins with the aim to obtain a full degradable

material at the end of its cycle life. These organic tanning processes allow obtaining leather to

be composted after usage.

This fact is becoming compulsory in Europe. The End-of-Life Vehicle Directive (or ELV

Directive 200/53/CE) requires the vehicle manufacturers be responsible for taking back and

scrapping cars in the future. Directive specifies that 95% of the vehicle weight must be reused

by 2015.

“Wet-white” is the intermediate leather commodity using the tanning properties of aldehydes,

mainly, glutaraldehyde22

. Other “wet-white” systems use metals like Aluminum, Zirconium,

Titanium when metals are admitted, vegetable tannins or syntans. Up-today, tara tannin is

intensively used to produce automotive “wet-white”, as a retanning agent after pre-tanning with

glutaraldehyde and the mechanical operations. Annex 3 shows a typical recipe to produce

automotive leather, “metal-free”, used for supplying of German car manufacturers. Its properties

of light fastness and relatively colorless have not been improved with other substances despite

the efforts of the chemical industry to find out a “synthetic tara tanning”.

Garment and glove industry is a traditional leather consumer. The men of the caverns already

used the skins of the animals, hunted for food, to keep worm. Through the tanning techniques,

especially with the chrome tanning technology, soft, light and very comfortable leather

22 Glutaraldehyde: C5H8O2, CAS number 111-30-8

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garments can be manufactured. Garment leather is produced mainly from sheep skins, de-

woolen or maintaining its natural wool.

Nowadays, with the development of new textile fabrics adding functionalities in terms of water

repellency, lightness, isolation and perspirability, the leather demand for garments is related to

fashion trends. However, classical nappa and suede (soft and light skins) and double-face

(woolen sheep skins) are very appreciated by luxury trademarks because its elegance and

natural feeling.

Luxury companies appreciate leather as a noble and natural material and produce leather goods

as complements in prestigious firms and recognized retailers. There is a high quality leather

demand for handbags, briefcases, wallets, belts… The natural properties of leather also are

related to country ambiances and are used in saddle, golf bags and many other accessories.

Table 8 summarizes market issues and tara consumption opportunities for each leather article.

Annex 6 describes the international leather production and it is detailed with figures and

statistics.

Footwear Furniture Auto Garment Gloves Other leather

goods

Market trend

Sustainable growing

higher than

population growth

rates

Stable Growing Variable Growing for

specific uses

Stable,

growing luxury

goods.

Main markets China, Italy, India,

Brazil

Italy, China,

Argentina

Germany,

Argentina, China,

Mexico, Brazil

Spain, China,

India, Italy,

Pakistan

South East

countries,

Africa

Spain, France,

Germany

Main

consumers Worldwide

Central and

North Europe,

USA

USA, Europe Europe USA USA, Europe,

Japan

Drivers Comfort, fashion,

functionalities

Elegancy,

design Elegancy, comfort Fashion

Compliance to

the end uses

Trademark

positioning

Leather

features

Soft, waterproof,

breathable

Surface

resistances,

light fastness

Very high technical

performances

Soft and

lightness

Soft and

fastness.

High quality,

elegance,

natural

Competition

materials Textile and plastics Textile Textile Textile Textile Plastics

Tara

opportunities Low Medium High Medium Medium High

Table 8 : Analysis for tara potential for the leather industry

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3.5. European Policy of Chemicals (REACH)

The European REACH Directive is a great opportunity for the trade of tara tannins in Europe23

.

Since 2006 there is a Directive in Europe (CE 1097/2006) concerning the Registration,

Evaluation, Authorization and Restriction of Chemicals (REACH).

To point out the most important advantage for tara products, compared with syntans and other

vegetable tannins, they are exempted of such Registration as defined in Annex V, #8:

“Substances occurring in nature, if they are not chemically modified, unless they meet the

criteria for classification as dangerous according to Directive 67/548/EEC”

According to Chapter 2, “Definitions and general provision”, Article 3, “Definitions”, # 39:

“Substances which occur in nature: means a naturally occurring substance as such,

unprocessed or processed only by manual, mechanical or gravitational means, by dissolution in

water, by flotation, by extraction with water, by steam distillation or by heating solely to remove

water, or which is extracted from air by any means”

Trading in Europe with tara powder or tara tannins extracted with water does not need to

incurred with tremendous cost required for collecting safety data and register them in REACH.

23 Oficial Journal of the European Union. Regulation (EC) No 1907/2006 of the European Paliament and of the Council of

18 December 2006. L 396/1. 30.12.2006

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4. Theoretic fundamentals

4.1. The Tanning science: the collagen chemistry

The process of tannage consists essentially in the production, from raw animal hides and skins,

residues of the food industry, of materials, normally referred to as leathers, which have a greater

stability to water, bacteria, heat and abrasion and have, as consequence a wide range of

domestic and industrial applications24

.

Leather is in downstream sectors of the consumer products industry. For the latter, leather is

often the major material input, and is cut and assembled into shoes, clothing, leather goods,

furniture and many other items of daily use25

.

The type of leather produced is to a large extent dependent on the origin (calf hides, cow,

sheepskin, goatskin, reptiles…) and previous treatment of the hides and skins but some control

may also be effected by the use of different tanning materials and by variation of the conditions

employed during tannage, e.g. temperature, pH, duration.

In the simplest terms of chemistry of leather manufacture is seen as the interaction of inorganic,

natural or synthetic tannins with the collagen fibers of the corium of skin.

Hides and skins contain three layers; the outer is the epidermis and the inner the subcutaneous

tissue. However, the intermediate layer, the dermis or corium, is the most valuable for the

tanners. Its constitution is mostly a protein, the collagen.

The earliest stages of the tanning process, the beamhouse operations, aim to remove the two

outer layers among other proteins from dermis, in order to purify, as much as possible, the fibril

structure of the collagen.

Currently, 30 different types of collagen have been described according its composition of

aminoacids and its sequence and depending on their function in the living organism.

Like keratin, elastin and silk fibroin, Type I collagen is a scleroprotein consisting like all

proteins of aminoacids liked by –CO-NH- groups to form peptide chains.26

The Type I collagen molecule is distinguished by its unusually high content of glycine, proline

and hydroxyproline which together account for over 50% of the amino acid content of the

protein. See table 9. This composition is crucial to the structure and reactivity.

24 E. Haslam. Chemistry of vegetable tannins. Department of Chemistry. The University, Sheffield, England, Academic

Press, London. 1966.

25 European Commission. Integrated Pollution Prevention and Control (IPPC). Reference document on Best Available

Techniques for the Tanning of Hides and Skins. 2003

26 Prof. Dr. rer. Nat. habil. Günter Reich. From Collagen to leather – the theoretical background. BASF Service Center.

Media and Communications. Ludwigshafen. Germany. 2007.

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Collagen is composed by three chains of polypeptides in α-helix form, as protofibrils and each

one contain approximately 1,000 aminoacids.

A collagen fibril is the union of 7,000 – 8,000 protofibrils and they come together to form fibers

of about 5 µm of diameter.

The content of acidic and basic amino acids, amino acids containing OH groups and peptide

groups is important and decisive for the reactivity of the collagen, which is a requirement for its

transformation into leather.

To understand the chemistry of the tanning processes, it should be taken into account that all the

reaction coordination and links with the tanning products is produced in the surface of the

collagen molecules formed by fibrils, by means, between the chemicals agents and the lateral

chains of aminoacids of collagen27

.

The most important reactive groups in the tanning process are:

Hydroxilic groups: from aminoacids serine, tyrosine and hydroxyproline

27 Josep Mª Morera. Química Técnica de la Curtición. Escola Universitaria d’Enginyeria Tècnica Industrial d’Igualada.

Escola Superior d’Adoberia. ISBN 84-931837-0-9.

Amino acids Content in % Number per molecule

Glycine 33.53 1056

Proline 11.97 377

Hydroxyproline 11.18 352

Aspargine 1.19 37

Aspartic acid 3.07 97

Glutamine 2.57 81

Glutamic acid 4.75 150

Lysine 3.17 100

Hydroxilysine 0.40 13

Arginine 5.04 159

Histidine 0.20 6

Serine 3.46 109

Trypophane 0.20 6

-CO-NH- 3147

Table 9: Type I collagen: content of amino acids. Source: Dr. G. Reich

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Carboxyl groups: from aminoacids aspartic acid and glutamic acid

Amide groups: from aminoacids aspargarine and glutamine

Amine groups: from aminoacids lysine, arginine, histidine, hydroxylysine.

Owning to the comprehensive information available on collagen, the modes of transformation

relevant to leather manufacture of the individual functional groups with the help of the

chemically widely disparate tanning agents are now known for the greater part28

. Table 10:

Functionality Bond type Typical tanning agents

Carboxyl groups Complex bonding Metallic salts, in particular

basic chromium (III)

sulphates

Basic groups Covalent bonding Aldehydes, diisocyanates, etc.

Peptide groups Hydrogen bonds Phenolic natural and synthetic

tanning agents

Surface overall Hydrophobic, “van der

Waals” bonds

Including polymers, tensides

Pores/capillarites Fillers Various substances

Table 10: The potential reactions on collagen during leather making

After flying, hides and skins have a higher number of chemical basic groups than acid groups,

thus, the pH value is between 7 and 8.

Figure 10: Diagram of the nature of leather formation by which "leatherlike drying out" is ensured by the crosslinking

and distance-enhancing action of the tannin agents. Source Dr. G. Reich

28 Prof. Dr. rer. Nat. habil. Günter Reich. From Collagen to Leather – the theoretical background. BASF Service Center.

Media and Communications. Ludwigshafen. Germany. 2007.

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The tanning operation is the treatment of hides and skins with chemicals in order to stabilize the

collagen structure from hydrolysis caused by water or enzymes and increase the heat resistance

higher that the natural temperature. Furthermore, tanning reactions have to avoid the union of

carboxyl and amino groups inside the collagen structure in order to obtain the required

properties of the leather suitable for its final uses or able to react with other chemicals to

achieve such features. Otherwise, when hides and skins are dried causes a fragile, hard and

translucent material well known as parchment.

The bound quantity of collagen is determined primary by stoichiometric aspects, but also

influenced by available surfaces on the fibrils, elementary fibers and fibers, and in the voids

between them (capillarities and pores).

The tanning materials exploiting these potential reactions on the collagen and the mechanism by

which they do so is now well understood, at least in basic terms29

.

Tanning chemicals must have more than one chemical functionality to be able to react with

more than one collagen molecule at the same time and to assure transversal bonds. Also, it is

important to consider both, their molecular size to be able to penetrate into the collagen

microstructure and its water solubility as tanning is made in water baths. Colloidal dispersion

with very small micelles and very disaggregate can have also, good tanning properties.

Furthermore the bonding chemical reactivity of the tanning substances and the protein structure

of the collagen net, diffusion and penetration concern the tanning processes. In principle, simple

stirring, the movement of a paddle wheels or movement of the drum used in tanneries to achieve

these mechanical effects, accelerate the diffusion process. However, the situation is different

where substances with an affinity for collagen are concerned. In these cases, the bond types and

the functional groups for the affinity are of secondary importance. The most important factor is

their accessibility to the collagen structure.

It is generally accepted that the penetration depth is dependent upon a diffusion coefficient k

multiplied by the square root of the tanning agent concentration and the duration of tanning, the

diffusion coefficient varying according the tanning agent type.

Pelts contain approximately 75% of water, a small part is bounded to the collagen and the

greater part is “free”, acting as a solvent and forming the “inner float”. This contrasts with the

“outer float” from a pit, paddle or drum in which the reacting substances are initially present

molecularly dispersed or in colloid suspension.

29 Prof. Dr. rer. Nat. habil. Günter Reich. From Collagen to Leather – the theoretical background. BASF Service Center.

Media and Communications. Ludwigshafen. Germany. 2007. Page 119

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As soon as the tanning substances reach the inner float from the outer float, it is taken up by the

collagen. This takes place from the outer layers towards the inside of the pelt. Provided the

supply of the substance remains below the saturation limit of the collagen, the process will

repeatedly restore the concentration gradient between the inner and the outer floats, and

diffusion will continue until complete exhaustion.30

However, there are facts to constrain the diffusion of the substances in the leather:

Astringency: happens when large-particle substances of high affinity, bonding of the

substance initially on the outer layers of the pelt may lead to blockage of the diffusion

paths.

Formation of aggregates: All tanning agents which owe their affinity for collagen to

their ability to form hydrogen bonds, tend to aggregate to form larger particles due to

such dipolar or “secondary valence” character.

Currently, the chemical industry provides the chemicals with tanning properties for the leather

industry. They offer mineral salts able to stabilize the collagen structure from hides and skins;

plant extracts (tannins); synthesized chemicals with tanning properties (syntans) and

commercializes tailor-made formulations to achieve products ready to be used in the tanneries.

Vegetable tannins are natural products of relatively high molecular weight which have the

ability to complex strongly with carbohydrates and proteins. The most common vegetable

extracts come from mimosa, quebracho and chestnut.

Among the mineral salts, the chromium III salts are, by far, the most used in the tanning

process.

4.2. Hydrothermal Stability

Hydroxyproline is an amino acid specific to collagen and substantially responsible for the

hydrothermal stability of native, fully hydrated collagen.

When collagen is wet, the matrix can be degraded by rising temperature, at the same time

hydrogen bonds in the triple helix are broken, observed as shrinking, leading to gelatinization.

The hydrothermal stability of collagen can be altered by many different chemical reactions, well

known in the fields of histology, leather tanning and other industrial applications of collagen.

30 Prof. Dr. rer. Nat. habil. Günter Reich. FROM COLLAGEN TO LEATHER – THE THEORITICAL BACKGROUND.

BASF Service Center. Media and Communications. Ludwigshafen. Germany. 2007. Page 43

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The effects of some of these chemical modifications can be summarized in table 11, where the

denaturation temperature is typically measured by the perceptible onset of shrinking31

:

Chemical modification Denaturation

temperature ºC

None 60

Metal salts: Al(III), Ti(IV), Zr(IV) 70-85

Plant polyphenol gallotannin or ellagitannin 75-80

Plant polyphenols: flavonoid 80-85

Synthetic tanning agent: polymerized phenols 75-85

Aldehyde: formaldehyde or glutaraldehide 80-85

Aldehyde: phosphonium salt or oxazolidine 80-85

Basic chromium (III) sulfate 105-115

Combination: gallotannin + Al(III) 105-115

Combination: flavonoid polyphenols + oxazolidine 105-115

Table 11: Effects of chemical modifications on shrinking temperature

The increase in hydrothermal stability has frequently been regarded as the characteristic

indicating completion of tannage crosslinking32

. It is undisputed that the shrinkage temperature

Ts which is based upon it is a quantity of interest in tanning theory. It provides an indication of

various types and grades of crosslinking, and its isometric measurement yields considerable

information on the modification which the collagen / leather structure has undergone. A.D.

Convington has attempted to formulate a new tanning theory encompassing all tanning

processes on the basis of detailed thermodynamic discussions33

.

However, it provides little indication of the practical value of the leather, as wet leather is

seldom subjected to thermal load during processing and use. Attainment of as high a Ts value as

possible is not an objective in the development of new tanning methods.

31 A. Convington, L. Song, O. Suparno, H. Koon, M.J. Collins. Link-Lock: An explanation of the chemical stabilization of collagen. World Leather. October/November 2010

32 Prof. Dr. rer. Nat. habil. Günter Reich. From collagen to leather – The theoretical background. BASF Service Center.

Media and Communications. Ludwigshafen. Germany. 2007. Page 115

33 A. Convington, G. Lampard, R. Hanco*ck, I. Ioannidis. Studies on the origien of hydrothermal stability. A theory of

tanning. Journal of the American Leather Chemists Association, 93 (1998), 107

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4.3 Current tanning practices, processes and techniques for leather

The production process in a tannery can be split into four main categories: hide and skin storage

and beamhouse operations, tanning operations, wet-end operations and finishing operations.

After the hides and skins are flayed from carcass at the abattoirs, they are delivered to the hide

and skin market or directly to the tanneries. Where necessary, hides and skins are cured before

transport to prevent them from putrefying. Upon delivery to the site, hides and skins can be

sorted, trimmed, cured and stored pending operations in the beamhouse.

Table 12 is a general overview of making leather from raw hides and a short description of

them34

can be found in Annex 7, always, will depend of the raw materials and the desired final

articles.

Table 12: Process steps for the production of leather from raw hides. Source: BREF

34 Reference Document on Best Available Techniques for the Tanning of Hides and Skins. 2003. Pag. 17.

Chrome tanned

leather

Upper leather Sole leather

Raw hides Preliminary soaking Soaking

Soaking

Liming Liming Liming

Flesing Fleshing Fleshing

Splitting Splitting

Tanning Deliming Deliming, bating Deliming

Bating Washing, Drippping Bating

Pickling Vagetable pit Vegetable pit

Chorme tanning tanning tanning

Samming Dripping, washing Washing

Samming Samming

Wet-blue Shaving Shaving

Washing Fatliquoring (drum) Fatliquoring

Neutralization Dryeing Dryeing

Wet-end Washing Retanning

Retanning Dyeing

Dyeing, fatliquoring Fatliquoring (drum)

Washing Samming, washing

Drying Drying

Crust Buffing Staking

Finishing Lacquering Buffing

Mechanical Toggling Staking

finishing Ironing (Rolling)

Leather article

Vegetable tanned leather

SoakingBeam-house

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4.4. Environmental considerations for the leather industry

The tanning industry is a potentially pollution-intensive industry. The environment effects that

have to be taken into account comprise not merely the load and concentration of the classic

pollutants, but also the use of certain chemicals. Of world tanneries, 80 – 90 % use chromium

(III) salts in their tanning processes. The degree of toxicity of chrome is perhaps one of the most

debated issues between the tanning industry and authorities. Annex 8 describes the main

environmental concerns in the tannery operations.

4.5. The vegetable tanning principles

It has been known since prehistoric times that raw skin is colored and rendered imputrescible

with aqueous solutions of materials obtained from many forms of plant life. Primitive peoples in

all parts of the globe and from all the ages of the past have developed vegetable tanning systems

based on materials available locally35

. Records exist relating to its operation in Mediterranean

regions around 1500 B.C. The active principle, which is widely distributed throughout the

vegetable kingdom, is a class of complex organic compounds, capable of combining with skin

protein, and known as tannin. By vegetable tanning is meant the combination of tannin with the

protein matter of skin to form leather.36

The plants have a particular ability to synthesize aromatic compounds37

, fundamental for their

metabolism. These aromatic compounds include aromatic amino acid (phenylalanine, tyrosine,

tryptophan) and aromatic phenolic and phenylpropenic acids. Tannins are the results of

condensation reaction of substances containing phenolic and carboxylic groups and are widely

distributed in the vegetal kingdom but very low concentrations. Gallic acid (C6H2(OH)3COOH)

participates in many of these condensation reactions (Figure 11).

Figure 11: Gallic acid

35 Thomas C. Thorstensen. Practical Leather Technology. Robert E. Krieger Publishing Company. Malabar, Florida. USA.

1985

36 John Arthur Wilson. The Chemistry of Leather Manufacture. The Chemical Catalog Company Inc. New York. U.S.A.

1928. Page 391

37 Krysztof Bienkiewicz. Physical Chemistry of Leather Making. Rober E. Krieger Publishing Company. Malabar, Florida,

USA. 1983. Page 385

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Certain plant cells are very rich in tannin. In the living cell, the tannin occurs dissolved in the

cell sap and associated with other substances, including carbohydrates and salts. Carbohydrates

are able to link up with the tannin in some way so as to prevent its attack upon living

protoplasm. The tannin appears to be useful in some way in the metabolism of the plant but

their physiological function remains a mystery. It seems they have a certain effect controlling

enzyme reaction and act as inhibitors.

The vegetable tannins are polyphenols with a molecular weight in the range of 500 – 3000.

Among the materials which have assumed commercial importance as a source of tannins for

leather manufacture are barks, woods, leaves, twigs, fruits, pods and roots. Aqueous solutions of

tannins have an astringent taste; give dark blue or green colorations with iron salts, and

precipitate gelatin, other soluble proteins, and alkaloids from solution.

Attempts to isolate the pure tannins and to study their organic structures have proved exceeding

difficult. Tanning extracts obtained from different sources show very different properties, which

are due in a large measure to the foreign matter extracted with the tannin, such starches, gums

and other materials. Therefore, the extract is not a true solution but will contain suspended

insoluble materials that contribute to the leather producing building into the fiber of skins

certain characteristics of fullness of feel and resiliency which are features of the tanning

materials and methods used.

The application of vegetable tanning has been based on empirical skills and experiences but has

become a major field of work by leather chemists and scientists to understand the structure of

the vegetable tannins and the estimation of the tannin content of grinded parts of the plants or its

extracts.

Freudenberg (1938) classified plant tannins in two major groups according to their chemical

nature and structural characteristics. The hydrolysable tannins are readily hydrolyzed by mineral

acids or enzymes (tannase and emulsion) into sugar or a related polyhydric alcohol and a

phenolic carboxylic acid.

Depending on the nature of the phenolic carboxylic acid the hydrolysable tannins are usually

subdivided into gallotannins and ellagitannins (Figure 12). Hydrolysis of gallotannins yields

gallic acid while ellagitannins, hexahydroxydephenic acid.

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Figure 12: Hydrolysable gallotannins and ellagitannins

The condensed tannins are polyflavonoids in nature, consisting of chains of lavan-3-ol units.

The most common class of condensed tannins or proanthocyanidins are the procyanidins which

consist of chains of catechin or epicatechin. In contrast to hydrolyzed tannins, condensed

tannins undergo polymerization to the amorphous phlobaphens or tannins reds, under action of

acids38

.

There is not a clear theory of the vegetable tannin fixation yet despite this practice has been

investigated for decades.

The vegetable tannins are, thus, complicated mixtures of chemical components and it is difficult

to obtain their structure. Furthermore, the colloidal behavior39

and the hide protein condition the

chemical reactions. According to Thortensen, all factors are important: degree of opening of the

fibers, the availability of reactive groups for vegetable tanning, the degree of hydration, the

presence of salts, the extent of swelling of the skin… All the relationship between all these

factors includes synergies between them or, contrary, working against one to another. This

makes impossible to establish a structured mechanism for practical and controlled tanning

process. Tanner’s forums still discuss whether vegetable tanning process is an organic chemical

action or strictly a physical absorption. The explanation of these discussions is the number of

relatively simple principles of physical facts that seem to apply to the tanning process.

38 J.M. Garro Galvez, B. Riedls and A.H. Conner. Analyutical studies on tara tannins. Departement des Sciences du bois et de la Forêt, Centre de Recherche en Sciences et Ingénierie des Macromolécules, Université de Laval, Quebec. Canada.

USDA-Forest Service, Forest Products Latoratories, Madison USA. Holzforschung. Vol 51.1997. Pag. 235-243. Walter de

Gruyter. Berlin. Germany.

39 The stability of a colloidal dispersion is determined by the electrical difference of potential between the film of solution

wetting the particles and the bulk of the surrounding solution. According to Procter and Wilson theory, the astringency of a tan liquor in practice is assumed to be a function of the potential difference between the solution immediately in contact

with the tannin particles and the bulk of the tan liquor as well as the potential difference between the tan liquor and the

collagen jelly. J.A. Wilson. The Chemistry of the Leather Manufacture. Chemistry of the tannins. Page. 467.

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The most acceptable reaction is the bonding to the CO-NH linkage of the protein through the

phenolic hydroxyl group of the vegetable tannin, among other side reactions.

The curve of the fixation of vegetable tannin materials as a function of pH indicates a slope

downward from the strong acid range to a minimum near the isoelectric point, a rise to a minor

peak, and a fall.

Figure 13: Fixation curve of the vegetable tannins

The explanation of this behavior can be a function of the availability of hydrogen bonds or

hydrogen atoms on the protein and on the vegetable tanning material. pH values for the

vegetable tannins are from 5 to 7. The vegetable tannins are, therefore, un-ionized through the

range of the vegetable tanning. The protein increases its hydrogen ion fixation with the lowering

pH. This explains, at this point, that fixation is a reaction of the hydrogen ion with the protein.

The S curve, however, demonstrate that this reaction cannot be strictly explained as a chemist

phenomena. Increase of pH after the isoelectric point causes an increase in hydration of the

protein and the fixation of the tannin just at pH values just above the isoelectric point.

As vegetable tannage proceeds, the fiber is no longer dominated by water of hydration and

changes its ionic character as a result of the fixation of the vegetable tannins. The hydration

factor becomes less significant, and the eventual fixation curve is a smoother sweep from the

neutral pH range to a high fixation at the strong acid range.

Other considerations to take into account during the vegetable tanning process is the size of the

tannin molecules, often relatively large and chemical reactions can be blocked resulting in

eventual coating of the fibers and filling the voids of the hide with vegetable tanning materials.

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For an effective vegetable tanning these stoichiometric constraints oblige to follow a certain sort

of steps, starting with the chemical reaction between the vegetable tanning material and the hide

protein, the coating of the fibers and isolation of the reactive groups and, finally, the filling of

the physical voids in the leather. Therefore, the technicians accurately control the penetration of

the vegetable tannin materials into the hide or the skin. According the final leather article, they

will give more or less value to the dispersion of the tannins, the degree of penetration and the

degree of the filling properties. For heavy leather, where filling action and weight are important,

the colloidal character of the tannins will be considered more than the chemical nature, and

hides and skins are processed mainly in rockers. Light articles, aiming to achieve a full but soft

tannage with a minimum amount of material, the chemical aspects are more important and

process is carried out in drums.

Vegetable tannins, also contain other substances with influence in the tanning process. So called

non-tannins, they are tannins with low molecular size and weight, and with limited reactivity

with the collagen protein.

Annex 9 briefly describes the vegetable sources of tannins most widely use for tanning leather.

4.6. Analytical characterization of tara tannins

In general, to determine the quality of the vegetable tannins the following parameters are

examined:

Tannin content: To characterize the content of tannins in the tara powder, there is no yet

an approved standard method but a proposal has being submitted based on the filter

method40

. It determines tanning agents through filtration of all vegetable and synthetic

tanning products. It is based on indirect gravimetric analysis through fixing of the

absorbent compounds on low-chromed hide powder.

Non tannin content: They are organic compounds with low molecular weight and,

therefore, they do not have tanning capacity. Free gallic acid and other organic acids

content in the powder are non tannins compounds, as well as carbohydrates. They are

determined by gravimetry.

Insolubles: Are particles or aggregates, non soluble, but are component of the powder as

lignin and cellulose. The gravimetric method is used after filtering the sample with a

membrane of 0.45 microns.

40

ISO/IULTCS International Standard. Reference number ISO/FDIS 14088:2011; IULTCS/IUC 32:2011. “Leather –

Chemical tests – Quantitative analysis of tanning agents by filter mothod”.

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Total solids: is the quantity of non-volatile substances at 100ºC. They are calculated by

gravimetry.

Figure 14: Constituents of tara tannins

Garro Galvez, Rields and A.H. Conner41

evaluated the tannin content extracted from tara for its

utilization in wood adhesives. Spectrophotometric and chromatographic analyses were

performed before and after hydrolysis to quantify amounts of free and combined components.

The results obtained in this study show that gallic acid is the main constituent (53%) and it was

easily isolated by alkaline hydrolysis of the plant extract. In the total sugars present in the

extract (9.6%) glucose had the biggest concentration (3.1%). Other constituents were present to

a less important extent. Figure 14.

Figure 15: Galloylated quinic acid and structure of tara tannin

According to Horler and Nursten (1961) the principal components of tara tannins are based on a

galloylated quinic acid structure:

Thus, they differ from other members of the hydrolysable tanning group which are based upon

galloylated or ellagoylated hexose.

41 J.M. Garro Galvez, B. Riedls and A.H. Conner. ANALYTICAL STUDIES ON TARA TANNINS. Departement des Sciences du bois et de la Forêt, Centre de Recherche en Sciences et Ingénierie des Macromolécules, Université de Laval,

Quebec. Canada. USDA-Forest Service, Forest Products Latoratories, Madison USA. Holzforschung. Vol 51.1997. Pag.

235-243. Walter de Gruyter. Berlin. Germany.

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For this reason, tara tannins are notable for their high acidity and on mild acid hydrolysis, the

tannin gives gallic acid, and instead of the usual carbohydrate fragment, the alicyclic quinic

acid. The acidity of the tannin is directly related to the presence in its structure of the free

carboxyl group of quinic acid42

.

4.7. The chemistry of the syntans

The modern operations of vegetable tanning, requires the use of auxiliaries to better control the

behavior of the tannins during the process, or to give or improve the final physical and fastness

properties and the quality of the final leather articles. With the aid of the chemical industry

during the 20th century and the knowledge of the organic synthesis, it is possible to obtain

molecules similar to the tannins or with special features to combine with them.

The syntans available to the leather industry are in constant evolution. The product ranges from

the chemical suppliers change very often to maintain their competitiveness as a result of

inversions in research programs. Nowadays, products and formulations are launched to the

market and the nature of the products is seldom revealed and they are kept confidential for

competitive reasons.

Stiasny observed the properties of the Gallic acid and concluded that products of phenol

sulphonic acid were able to condensate and react with the protein to produce leather. He was

first patenting a synthetic tannin or syntan.

The phenol is first sulphonated with sulfuric acid, to obtain a sulphonic acid that will be either

the alpha or beta position depending upon the temperature of the sulphonation. Figure 16.

Figure 16: Phenol sulphonation

The phenol sulphonic acid is condensed with formaldehyde. Figure 17.

42

E. Haslam. Chemistry of vegetable tannins. Academic Press. London and New York. 1966. Pag. 113.

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Figure 17: Condensation of phenol sulphonic acid

The tanning properties increase with the molecular size until certain limit. This happens because

they are not able to penetrate in the collagen structure. The sulphonic groups should be kept as

lower as possible, just to assure that the molecule is soluble.

The syntans based on phenol condensation are classified as “replacement” syntans. This is due

to those tanning properties, thus they are able to replace vegetable tannins.

In another hand, and with the same principles of condensation and sulphonation, naphthalene

syntans are the simplest and easiest to make. Naphthalene is a solid, aromatic compound with a

melting point of 80ºC43

. The material is melted and sulphuric acid is added for the formation of

the naphthalene sulphonic acid. The sulphonic acid is diluted with water and condensed with

formaldehyde. The condensation of formaldehyde binds some of the unreacted naphthalene, and

a completely water soluble product is obtained.

Figure 18: Naphthalene sulphonic acid

The material is strongly acid. The product may be marketed as an acid liquid to be applied in

formulations for whitening chrome leathers or bleaching vegetable tannins. It may also be

neutralized to form a neutral salt of the syntan which may be marketed as a liquid or often, dried

and as a solid syntan.

Naphthalene syntan is an example of a material capable of being absorbed by the hide protein

through hydrogen bonding. As the pH is lowered, the syntan is bound according to the curve of

the figure 11. The naphthalene syntan is a large organic molecule containing hydrophilic

sulphonic acid groups. It is, therefore, somewhat related to the detergents. The sulphonic acid

group pulls the molecule toward the water, whereas the aromatic naphthalene rings will be

43 Thomas C. Thortensen. Practical Leather Technology. Robert E. Krieger Publishing Company. Malabar. Florida. 1985.

Third edition. Page 172.

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attracted to other less soluble materials dispersed in the solution. When dissolved with the

vegetable tanning materials, the syntan adds negative charges to form a more negatively colloid

charges. The addition of negative charges to the vegetable tannin will aid in dispersing the

tanning particles and help in the penetration of the hide.

The naphthalene syntan will also compete with the vegetable tanning for the absorption

positions on the hide protein, and consequently, it will aid in the brightening of the color and the

penetration of vegetable tannins.

Since the fixation of the naphthalene syntan is based on the acid absorption phenomenon, the

reaction is not permanent and the syntan can be removed. It does not have leather-forming

properties in that the leather will not dry soft but will continue to dry hard and bony. There is no

real permanent stabilization of the hide fiber and only a slight raising of the shrink temperature.

For this reason, naphthalene sulphonic syntans are classified as “auxiliary” syntans and are used

mainly to confer supplementary properties to the main tanning agents, either vegetable tannins

or chromium salts.

A large number of different synthetic tannins are presently being offered in the leather industry.

As the molecules become more complicated, more specific tanning properties can be built into

them. Examples of the types of materials of various syntans are protected with patents by

various manufacturers.

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PART TWO: EXPERIMENTAL

5. Objectives of the experimental part

The experimental part of the research is intended to prove the hypothesis that the application of

tara tannins, known since remote eras, can respond as newest technologies of tanning leather

that comply quality article standards at the time to meet the highest exigencies of chemical

auxiliaries used in goods supply chains.

Section 6, consisting on chemical analysis carried out according the parameters described by the

chemistry industry detailed in section 4.6, aims to compare commercial samples of tara powder

from different suppliers of leather chemical auxiliaries and determine statistical significant

differences among them. Also the purpose is to have a range of parameters to validate the

results for all other experiments of carried out during this research.

A expedition to Bolivia was planned to identify areas where tara is found either wildly or

cultivated in forestry farms. During the trip, samples of tara fruits were collected and its

components characterized to determine the feasibility of its commercialization. Therefore,

section 7 aims to compare the samples of tara fruits among them and with the range of the

analytical values obtained in the section 6.

The market analysis described in section 3 pointed out the needs of standardization to improve

international requirements by offering a range of quality products. As a natural source, many

conditions, such a climatic, soil, altitude and many others may cause differences in the chemical

composition of the fruits.

Section 7 includes the determination of the gallic acid content. This will give an idea of the

hydrolysis of the tara tannins and whether this characterization can be used to test the quality of

the tara products. Also, the hydrolysis of the tara tannin will be tested to confirm the

classification of tara tannin as hydrolysable vegetable tannin as described in section 4.5.

Section 8, 9 and 10 statistically analyze the results of the experiments designed with the support

of the Statgraphics Plus software, version 5.0 from Statpoint Technologies, Inc (Warrenton, VA,

USA)44

. In all cases, the considered dependent variables will be the hydrothermal stability

calculated with the shrinkage temperature according section 4.2, the measurement of the tensile

strength and elongation and the measurement of the tear load. All these physical properties are

common required for most of the leather article quality specifications.

44 Bacardit A., L. Ollé. Diseño de experimentos en ingeniería del cuero. Escola d’Enginyeria d’Igualada. escola Superior

d’Adoberia d’Igualada. ISBN: 84-931837-8-4

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Blends of tara powder with a naphthalene sulphonic syntan and a phenol condensate syntan as

auxiliaries for the pretanning process, section 8, experimental design 1, were calculated with a

Simplex with centroids method.

Section 9 will optimized the blend composition ratios of tara powder and the syntan. Design II

is based on quadratic, orthogonal, centralized and rotatable model to analyze best fitted variable

response surface.

This composition will be afterward applied under certain conditions, by means pH measurement

previous and after pretanning operation, Section 10. Design III will be also based on quadratic

orthogonal, centralized and rotatable model to analyze best fitted variable response.

Section 11 will consist in the manufacturing of an automobile-interior leather article from wet-

white processed with tara, at pilot scale and according the results of the experiments. The

leather will be treated later a regular recipe of retanning, fatliquoring, dyeing, mechanical

operations and finished by coating, as described in section 4.3. The leather article will be tested

for physical properties according the ISO standards of article specification.

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6. Characterization of commercial tara powder

Four commercial samples were collected from four specialty leather chemicals suppliers. as

common practice, there were no indication of the origin of the tara pods where they were

harvested or processed. All of them, however, indicate that the commercial products were

imported from Peru and they were not been chemically treated. Therefore, it must be assumed

that the tara powder was processed as described in section 2.4.

Physical appearance of samples were similar, a fine yellowish-light brown powder.

Tests of characterization were carried out in the laboratory according to descriptions in section

4.6 with the following results:

Determination Sample 1 Sample 2 Sample 3 Sample 4

pH analytical solution 3.4 3.5 3.3 3.5

Soluble solids (%) 74.5 67.9 59.8 59.70

Total solids (%) 89.0 92.2 93.6 92.90

Non tannins(%) 15.0 17.9 10.9 14.70

Tannins(%) 59.5 50.1 49.0 45.0

Insoluble(%) 14.5 24.2 33.8 33.20

Water(%) 11.0 7.8 6.4 7.10

Table 13: Characterization of 4 commercial samples of tara powder

6.1. Analysis summary of commercial tara commercial samples

The analysis method was based on creating individual charts for each determination or variable.

It allowed confirming whether the data came from a process which is in a state of statistical

control. The control charts were constructed under the assumption that the data came from a

normal distribution.

6.1.1. Data variable: pH analytical solution

Analysis Summary: 4 values ranging from 3.3 to 3.5

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Table 14: Analysis summary for pH (commercial samples)

Average = 3.42

Variance = 0.10

Standard deviation = 0.10

Minimum = 3.30

Maximum = 3.50

Range = 0.20

Stnd. skewness = -0.70

Stnd. kurtosis = -0.53

Table 14 shows summary statistics for pH. It includes measures of central tendency, measures

of variability, and measures of shape. Of particular interest here are the standardized skewness

and standardized kurtosis, which can be used to determine whether the sample comes from a

normal distribution. Values of these statistics outside the range of -2 to +2 indicate significant

departures from normality, which would tend to invalidate any statistical test regarding the

standard deviation. In this case, the standardized skewness value is within the range expected

for data from a normal distribution. The standardized kurtosis value is within the range

expected for data from a normal distribution.

Number of observations = 4

0 observations excluded

X Chart

UCL : +3,0 sigma = 3.87

Centerline = 3.42

LCL : -3,0 sigma = 2.98

0 beyond limits

Estimates

Process mean = 3.42

Process sigma = 0.15

Mean MR(2) = 0.17

Table 15: Normal distribution for pH

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The mean is equal to 3.42 and the standard deviation equal to 0.15. Since the probability of

seeing 0 or more points beyond the limits just if the data comes from the assumed distribution,

we cannot reject the hypothesis that the process is in a state of statistical control at the 90%

confidence level.

6.1.2. Data variable: Tannins (%)

Analysis Summary: 4 values ranging from 45.0 to 59.5

Table 16: Analysis summary for tannins (%)

Average = 50.90

Variance = 37.67

Standard deviation = 6.14

Minimum = 45.00

Maximum = 59.50

Range = 14.50

Stnd. skewness = 1.00

Stnd. kurtosis = 0.91

Table 16 shows summary statistics for Tannins. In this case, the standardized skewness value is

within the range expected for data from a normal distribution. The standardized kurtosis value

is within the range expected for data from a normal distribution.

Number of observations = 4

0 observations excluded

X Chart

UCL : +3.0 sigma = 63.75

Centerline = 50.90

LCL : -3.0 sigma = 38.05

0 beyond limits

Process mean = 50.9

Process sigma = 4.28

Mean MR(2) = 4.83

Table 17: Normal distribution for tannins (%)

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The mean is equal to 50.90 and a standard deviation equal to 4.28. Since the probability of

seeing 0 or more points beyond the limits if the data comes from the assumed distribution, we

cannot reject the hypothesis that the process is in a state of statistical control at the 90%

confidence level.

6.1.3. Data variable: Non-Tannins (%)

Analysis Summary: 4 values ranging from 4 values ranging from 10.9 to 17.9

Table 18: Analysis summary for Non-tannins (%) (commercial samples)

Average = 14.62

Variance = 8.25

Standard deviation = 2.87

Minimum = 10.90

Maximum = 17.90

Range = 7.00

Stnd. skewness = -0.38

Stnd. kurtosis = 0.64

Table 18 shows summary statistics for Non tannins. In this case, the standardized skewness

value is within the range expected for data from a normal distribution. The standardized

kurtosis value is within the range expected for data from a normal distribution.

Number of observations = 4

0 observations excluded

X Chart

UCL : +3,0 sigma = 26.77

Centerline = 14.62

LCL : -3,0 sigma = 2,48

0 beyond limits

Process mean = 14.62

Process sigma = 4.05

Mean MR(2) = 4.57

Table 19: Normal distribution for Non-tannins (%)

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The mean is equal to 14.62 and a standard deviation equal to 4.05. Since the probability of

seeing 0 or more points beyond the limits if the data comes from the assumed distribution, we

cannot reject the hypothesis that the process is in a state of statistical control at the 90%

confidence level.

6.1.4. Data variable: Insolubles (%)

Analysis Summary: 4 values ranging from 4 values ranging from 14.5 to 33.8:

Average = 26.42

Variance = 82.48

Standard deviation = 9.08

Minimum = 14.50

Maximum = 33.80

Range = 19.30

Stnd. skewness = -0.72

Stnd. kurtosis = -0.45

Table 20 shows summary statistics for Insolubles. In this case, the standardized skewness value

is within the range expected for data from a normal distribution. The standardized kurtosis

value is within the range expected for data from a normal distribution.

Table 20: Analysis symmary for Non-tannins (%) (commercial samples)

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Number of observations = 4

0 observations excluded

X Chart

UCL : +3,0 sigma = 44.07

Centerline = 26.42

LCL : -3.0 sigma = 8.78

0 beyond limits

Process mean = 26.42

Process sigma = 5.88

Mean MR(2) = 6.63

Table 21: Normal distribution for insolubles (%)

The mean is equal to 26.42 and a standard deviation equal to 5.88. Since the probability of

seeing 0 or more points beyond the limits if the data comes from the assumed distribution, we

cannot reject the hypothesis that the process is in a state of statistical control at the 90%

confidence level.

6.2. Conclusion characterization of commercial tara powder

Considering the normal distribution, all the variable results of the chemical tests carried out to

consider the quality consistence of the four commercial tara powder analyzed, do not show

significant statistic differences. Therefore, Table 22 indicates reference values for tara

characterization that will be used for the next experimental parts of this research. The higher

value corresponds to the mean value plus standard deviation and the lower the mean value

minus the standard deviation:

Determination Values Higher Lower

pH analytical

solution

3.42 3.57 3.27

Soluble solids (%) 65.53

Total solids (%) 91.95

Non tannins(%) 14.63 18.67 10.58

Tannins(%) 50.90 55.18 46.62

Insoluble(%) 26.43 32.31 20.54

Water(%) 8.05

Table 22: Reference values of tara characterization

To carry out the trials in the following experimental part, any of the samples can be validated as

deviations on results remain under a normal distribution.

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7. Characterization of tannins from Bolivian tara fruits

7.1. Description of samples

Samples of tara fruit were collected from five different Departments in Bolivia, La Paz, Santa

Cruz, Potosí, Cochabamba and Chiquisata in August 2009.

The samples were prepared at the origin with a mixture of fruits coming from, at least, 5

different trees. Each sample was weighted to 1.1 kg, packed in plastic sacks and properly

labeled.

Photo 2: Samples of tara fruit collected in Bolivia

The tara fruits were constituted with a brownish-orange pod and, internally, dark brown seeds.

Pods sized between 8 to 10 cm long and 2 cm wide. Each pod contained between 4 and 7 round

seeds of 0.6-0.7 mm diameter.

Samples were very dry and there were no differences on humidity content after drying the

samples at 30ºC during 4 o 7 days:

Origin Humidity % (drying 4 days) Humidity % (drying 7 days)

La Paz 1.4 1.4

Santa Cruz 3.2 3.2

Potosí 1.8 1.9

Cochabamba 1.2 1.2

Chiquisata 2.6 2.6

Table 23: Humidity content of tara fruits

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7.2. Preparation of the samples:

Samples were manually prepared by splitting the pods and the seeds.

Once the seed were separated, the pods were grounded and sieved to 250 µm. The fibers of the

cellulosic material remained in the thicker fraction, and the powder was sieved to 150 µm. In

this case, the thicker fraction was milled again until the particle size was hom*ogenized.

Photo 3: Components of the tara fruit samples from Bolivia (seeds, fibers and powder).

7.3. Composition of the fruits:

The fractions obtained during the preparation of the samples were weighted with an analytical

balance:

Origin % Seed % Fiber % Powder

La Paz 44.3 9.0 46.6

Santa Cruz 47.5 6.7 45.8

Potosí 35.4 8.1 56.5

Cochabamba 46.7 6.9 46.4

Chiquisata 49.5 9.0 41.5

Table 24: Composition of the fruits

The sample coming from Potosí was the poorest in seed content, but richest in powder.

Chiquisata’s sample was the richest in seed and fiber, but the poorest in powder.

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7.4. Characterization of the tara powder

Tannins were determined by filter method, indirect gravimetric analysis with fixing of the

absorbent compounds in a low-chromed hide powder45. Results were compared with the values

of commercial tara obtained in Section 6.

La Paz Santa Cruz Potosi Cochabamba Chiquisata Reference

Non tannin 11.30 17.60 11.70 13.40 17.20 14.63

Tannin 60.30 50.90 59.40 55.70 50.70 50.90

Soluble solids 71.60 68.50 71.10 69.10 67.90 65.53

Insoluble 21.00 22.00 20.10 22.90 23.70 26.43

Total solids 92.60 90.50 91.20 92.00 91.60 91.95

Water 7.40 9.50 8.80 8.00 8.40 8.05

Table 25: Chemical characterization of tara powder from Bolivian samples

By comparing the values of table 25 with the table 22 where the higher and lower values were

determined by the standard deviations, there is a clear consistency. Only two values are above

the values of the normal distribution with higher tannin content, La Paz and Potosí.

Therefore, the tara fruit collected in Bolivia during this work has a good quality to be valorized

in the market of the tara powder and can be considered as a consistence sustainable source of

tannins for the leather industry. To point out that the sample coming from Potosí was the richest

in powder and tannin concentration with the lower content of insolubles.

Theoretically, we calculated soluble and insoluble solids in dry conditions with the aim to

obtain more quality data.

La Paz Santa Cruz Potosi Cochabamba Chiquisata Reference

Soluble solids 77.32 75.69 77.96 75.11 74.13 71.26

Insoluble 22.68 24.31 22.04 24.89 25.87 28.74

Table 26: soluble / insoluble matter content in dry conditions

45 Hide powder with certificate for analysis of substances released by hide powder in contact with distilled water (blank

value) was purchased from FILK, Meissner Ring 1-5, 09599 Freiberg, Germany. www.filkfreiberg.de

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Figure 19: Bar chart of soluble and insoluble matter of tara powder

The highest insoluble matter in the commercial reference means that production factories do no

separate properly the cellulosic fibers during the milling process. This is a potential action to

improve the quality of the tara powder. A certain contamination from the mills to the product is

also plausible.

The relationship between the tannin and the non-tannin content in the tara powder could be used

also as a reference of the quality of the powder and it can be correlated to the degree of

hydrolysis.

This relation is calculated without the effects of humidity and insoluble matter content in the

tara powder:

La Paz Santa Cruz Potosi Cochabamba Chiquisata Reference

Non tannin 15.78 25.69 16.46 19.39 26.33 22.32

Tannin 84.22 74.31 83.54 80.61 74.67 77.68

Table 27: Tannin / non tannin content of tara powder

Figure 20: Tannin /non tannin content of tara powder

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The tanning content of the commercial tara powder reference is similar to the samples of the

tara powder of trees from Santa Cruz, Cochabamba and Chiquisata. La Paz contains the higher

amount of tannin followed by the sample from Potosí.

The highest content of non tannin could be compared with the content of free gallic acid as a

result of a certain hydrolysis. It was described in Section 4.6, Figure 14, the chemist

composition of the tara tannin by 53% of gallic acid and 10% sugar.

As tara tannin is hydrolysable, the content of free acid gallic can be determined and quantified

by high-performance liquid chromatography (HPLC) chromatographic technique.

To optimize this method, several tests were carried out with different elusion gradients.

The following conditions were considered to obtain the best results:

Instrument : Agilent 1200 chromatograph

Column : Zorbax eclipse XBC C-18 (Agilent)

Gradient: A=80% H2O / HCOOH (999 / 1 v/v) + B=20% Methanol /

HCOOH (999 / 1 v/v), in 15 min 100% B

Injection volume : 10 µL

Flux : 1 mL/min

Temperature: 25ºC

Calibration curve of gallic acid (Panreac) is calculated to proceed with analytic determination of

tara powder samples.

For the calibration curve, 5 watery analytical solutions are acidified with 1% formic acid to the

following concentrations: 0.5, 1, 2.5, 5, and 10 mg/L. Samples are analyzed by HPLC and

calibration was calculated through the area graphic of the obtained pick of gallic acid against the

concentration.

Figure 21: Calibration curve of Gallic acid for HPLC

To quantify the gallic acid content for each sample, a 2% of tara solution was prepared and the

analytical solution was diluted 1/20. The analysis was carried out according the described

conditions:

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Figure 22: Determination of free Gallic acid of a commercial tara powder by HPLC

Figure 23 compares the HPLC chromatographic curves for the tara powder obtained from the

samples of tara fruits collected in different departments in Bolivia.

The resulting values of free gallic acid content are shown in table 28:

Sample Gallic acid content (mg/kg)

La Paz 759

Santa Cruz 2704

Potosí 738

Cochabamba 684

Chuquisata 790

Commercial reference 1727

Table 28: Content of Gallic acid in tara powder samples

We can analyze the results of gallic acid coming from the HPLC and the non-tannin content:

Regression Analysis – Linear model: Y = a + b*X

Dependent variable: Gallic acid

Independent variable: Non Tannin

Analysis of Variance

Source Sum of Squares Df Mean Square F-Ratio P-Value

Model 1.19077E6 1 1.19077E6 1.89 0.2632

Residual 1.89348E6 3 631161.0

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Figure 23: Chromatography of tara powder from Bolivian fruits. Red arrow indicates the content of gallic acid.

The output shows the results of fitting a linear model to describe the relationship between Gallic

acid and Non Tannin. The equation of the fitted model is

Gallic acid = -1225.03 + 114.97*Non Tannin

Since the P-value in the ANOVA table is greater or equal to 0.10, there is not a statistically

significant relationship between Gallic acid and Non Tannin at the 90% confidence level:

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Figure 24: Plot of fitted model for gallic acid and Non Tannin

Therefore, the statistic values of the current analysis are not able to precise a correlation

between the non-tannin content and the hydrolyzed gallic acid and other molecules, such sugars

and primary condensation, as the null hypothesis cannot be rejected. The content of gallic acid

cannot be considered as analytical method for test tara powder quality.

However, as described in 2.4, gallic acid has a high demand in other markets as a worth

polyphenol. Despite “other applications” are not in the scope of this work, the degree of

hydrolysis with the temperature will validate that tara tannin is a hydrolysable tannin.

A 2% solution of a commercial tara powder was exposed to different temperatures (30º, 100 and

136ºC) during 1 hour and is analyzed by HPLC according the method described above.

Hydrolysis conditions Free Gallic Acid (mg/kg)

Hydrolysis at 30ºC during 1 hour 1725

Hydrolysis at 100ºC during 1 hour 2743

Hydrolysis at 136ºC during 1 hour 3439

Table 29: Results of hydrolysis test of commercial tara powder

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Figure 25: Chromatogram of hydrolyzed tara powder

Figure 25 remarks the pick of Gallic Acid in the chromatograph and, by visual comparing with

Figure 22, the difference is quite evident:

Despite the simplicity of this experiment it gives an idea that there exists a relation between the

temperature of hydrolysis and the content of free gallic acid.

Data can be statistically analyzed considering that the content of free gallic acid (variable) is the

result of the effect of every level considered in the temperature and a residual effect. The

mathematical model is:

xij = Gi + zij Gi = A + Bj

i = 1, 2, … r (levels) → 30, 100, 136

j = 1, 2, … c (replicates) → 0 ( there is only on test for the commercial tara

powder)

A = Constant

Bj is a parameter depending of the level i and represents a deviation of Gi with

regards to the reference constant A

Source Sum of Squares Df Mean Square F-Ratio P-Value

Model 1.47E6 1 1.47E6 174.2 0.0481

Residual 8460.12 1 8460.12

Multiple Regression Analysis

Dependent variable: Gallic Acid

Parameter Estimate Error Statistic P. Value

CONSTANT 1224.10 119.44 10.25 0.0619

Temperature 15.93 1.21 13.20 0.0481

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The output shows the results of fitting a multiple linear regression model to describe the

relationship between Gallic Acid and temperature. The equation of the fitted model is

Gallic Acid = 1224.1 + 15.9*T

Since the P-value in the ANOVA table is less than 0.05, there is a statistically significant

relationship between the variables at the 95% confidence level

The R-Squared statistic indicates that the model as fitted explains 99.43% of the variability in

Gallic Acid. The adjusted R-squared statistic, which is more suitable for comparing models

with different numbers of independent variables, is 98.86%. The standard error of the estimate

shows the standard deviation of the residuals to be 91.98. The mean absolute error (MAE) of

49.23 is the average value of the residuals.

In determining whether the model can be simplified, notice that the highest P-value on the

independent variables is 0.0481, belonging to temperature. Since the P-value is less than 0.05,

that term is statistically significant at the 95% confidence level.

Figure 26: Plot of fitted model for free Gallic acid and temperature

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8. Pretanning process. Design I: blending with syntans

In order to propose an innovative wet-white solution for a sustainable pretanning process using

tara tannins, the work will be split in three experimental designs:

The first experimental design will focus on finding the best combination of tara with syntans, by

means, blending the tara powder with a condensation phenol syntan or a naphthalene sulphonic

syntan, or the three of them.

For this selection, the shrinkage temperature, the measurement of tensile strength and

percentage elongation (EN ISO 3376 – IUP646,47

) and the Measurement of tear load (EN ISO

3377-2, IUP848

) were evaluated49

.

As discussed in section 2.4, tara is well appreciated in the leather industry as vegetable tanning

agent because its light fastness compared with other vegetable tannins. Therefore, influences of

the components of the different mixtures on this feature will be also assesed.

According to the results of the first experimental design, and evaluating the same parameters,

further tests are carried out to obtain the best recipe for a pre-tanning wet-white.

8.1. Products, materials and equipment. Design I

To carry out the experimental tests, the following commercial products were selected:

Synthetic tanning of phenol condensation:

Fine powder, white, soluble in water. 95% of tanning content, pH 4 (+/-0.2) solution 1:10

46 J. FONT. Análisis y ensayos en la industria de curtidos. Escola Universitària d’Enginyeria Tècnica d’Igualada. Escola

Superior d’Adoberia d’Igualada. ISBN: 84-931837-5-X

47 Normas IUP. Ensayos Físicos de Curtidos. Asociación Química Española de la Industria del Cuero. AQEIC. Octubre

2001. Pag. 20

48

Normas IUP. Ensayos Físicos de Curtidos. Asociación Química Española de la Industria del Cuero. AQEIC. Octubre

2001. Pag. 29.

49 The physical tests on leather determine the capacity of finished leather to resi st loads and actions that will be submitted

by consumers according the manufactured leather goods. Such tests measure the properties that depend on the whole

leather structure, considering all its thickness. The results will depend on factors like the part s of the hides or skins where samples are taken and its dimensions, the technical characteristics of the apparatus, the atmospheric conditions and the

procedures. Therefore, the standard ISO methods have to be strictly followed to assure the maximum repeti tiveness and

reproducibility.

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Synthetic tanning of naphthalene sulphonic:

Yellowish liquid. Miscible in water. 40 % of tannin content. pH 3.3 – 3.7 (solution 1:10)

Tara Powder: Origen: Peru

Quality Control pH 3.5 Insolubles 32 %

Tannin content 47 % Soluble solids 60 %

Non tannin content 13 % Total solids 92 %

Water 8 % Iron 388.9 mg/kg

(ppm) by atomic

absorbance

Trials were carried out using the following drums:

Deliming, bating and pickling:

Simplex DF drum, stainless steel, 1000 x 500 mm (DxL). Annex 10

Pretanning process:

2 – Fave drums, stainless steel, 500 x 200 mm (DxL). Annex 11

Comparative tests were carried out on Russian bovine hides, green split. They were divided in 8

pieces and marked. The eight pieces were weight and their thicknesses were calibrated.

Figure 27: Sampling hides for testing

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Deliming, bating and pickling treatment were carried out according the recipe in table 30:

Operation ºC % Product Time Comments

Washing 30 150 Water

0.2 Lactic acid 20 min. Drain

Deliming 35 100 Water 6 rpm

2.5 Ammonium sulfate

0.3 Sodium bisulfite

0.8 Lactic acid 90 min pH = 8.1

Cut through

Bating 1 Enzyme 60 min Check bating

pH 7.9

Drain

Washing I 20 200 Water 15 min Drain

Washing II 20 200 Water 15 min Drain

Pickling 20 50 Water 8 rpm

10 Sodium chloride 15 min

0.5 Formic acid (1:10) 20 min

1.0 Sulfuric acid (1:10) 120 min

Run

overnight

pH 3.5

Cut through

0.1 Preservative 15 min Drain

Horse up

Table 30: Deliming, bating and pickling

8.2. Process and tests. Design I.

The experimental design to evaluate ingredient blends, for the first step, is the Simplex method.

It is applied when the sum of the percentages of the two or more factors or ingredients of a

blend must be 100%. Therefore, the levels of the factors are not independent and the variation of

them can determine the properties of the final product.

If x1, x2, …, xn are the variables representing the percentages of k ingredients or components of

a blend, the values of xi are restricted as follows:

0 ≤ xi ≤ 1 I = 1, 2, ..., k

and the sum of the percentages of the k ingredients is 1:

Σ(i=1…k) xi = x1 + x2 + … + xk = 1

If the percentage of a component is xi = 1, than there are no other components in the mixture.

To design a blend with three components, the coordinated values are defined as:

x1 + x2 + x3 = 1

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The geometric description of the space of the factors for k components is a Simplex of (k-1)

dimensions. Therefore, for three component blend, it will be a triangle which vertex represents

one single component and the sides are the designed coordinates for mixtures of two

components and a xi=0. The coordinates inside the triangle represent the mixtures of two

components where x1 > 0, x2 < 0 and x3 < 0. Any proportional combination of components for

the mixture experiment must be placed either in the frontier or inside the triangle of coordinates.

The axes of the variables xi in the Simplex system of three variables are drawn in the figure 25.

The axis of the ingredient i is the straight line that goes from the point base xi=0 and xj=1/(k-1)

for the ingredients, j≠i in the vertex, where xi=1 and xj=0 for j≠i.

Figure 28: Coordinate axis for a mixture of three ingredients

As an example, for the mixture of three ingredients, the axis x1 goes from the base of

coordinates (0, ½, ½) to the vertex (1, 0, 0):

The Simplex design with centroids is based in the Simplex system coordinates when mixtures

containing 1, 2, 3… or k ingredients with identical proportions. This means that there are k

mixtures for each ingredient: all possible mixtures for two components is ½, for three 1/3 for k,

1/k. The trials are designed according to Simplex with centroids coordinates, and the

percentages are adjusted to the tannin content of each ingredient according table 31:

x1=1

(0,1,0)

x2=1

(0,0,1)

x3=1

(1,0,0)

(½, ½,0) (½, 0,½)

(0,½, ½)

x1 axis

x2 axisx3axis

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Test X1 X2 X3 Tara Phenol syntan Naphtalen

sulphonic syntan

1 1 0 0 12 0 0

2 0 1 0 0 6 0

3 0 0 1 0 0 14

4 1/2 1/2 0 6 3 0

5 1/2 0 1/2 6 0 7

6 0 1/2 1/2 0 3 7

7 1/3 1/3 1/3 4 2 4.7

Table 31: Simplex with centroids design

The pretanning trials are carried out according to the following general process:

Operation ºC % Product Time Comments

Pre-tanning 20 50 Water

4 Sodium chloride 15 min ºBè: 7

pH 3.5

1/2 Tanning agent

2 Sulphitated fatliquor 120 min Note 1

1/2 Tanning agent Overnight Note 2

0.5 Formic acid 90 min pH 3.2

Drain

Horse up. Samming. Pasting 12 hours at 30ºC. Conditioning and stake.

Notes:

Test 1:Tara powder

Note 1: pH=4 (paper indicator). Through tanning ½ in the flesh side with ferric

chloride. Insolubles are quite visible.

Note 2: pH=4 (paper indicator). Checked with ferric chloride, a thin inside layer

remains untanned. The bath is exhausted and insolubles are visible. Grain is shrunk,

grey color. Leather is full and round. Thickness 3.5/3.7 mm (2 mm before pretanning).

Test 2: Phenol syntan

Note 1: pH=3.8 (paper indicator). Through tanned (checked with brome-cresol green indicator).

Leather is clean and white.

Note 2: pH=4. Through tanned (checked with brome-cresol green indicator). Bath is exhausted.

Smooth grain, white and clean.

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Test 3: Naphthalene sulphonic syntan

Note 1: pH=3.8. Through tanned (checked with brome-cresol green indicator). Leather is clean in

both sides, flesh and grain.

Note 2: pH=4. Through tanned (checked with brome-cresol green indicator). Bath is exhausted.

Smooth grain. Leather is clean in both sides, flesh and grain.

Test 4: Tara + phenolic

Note 1: pH=3.7. Through tanned (checked with brome-cresol green indicator), but ferric chloride

indicates 1/3 tara penetration. Insolubles are visible.

Note 2: pH4. Through tanned (checked with brome-cresol green indicator and ferric chloride).

Insolubles are visible.

Test 5: Tara + naphthalene sulphonic

Note 1: pH = 3.5 (paper indicator). 85%through tanned with syntan and 50 with vegetable

tannin. Insolubles are visible.

Note 2: pH=4 (paper indicator). An untanned thin layer is visible and checked with ferric

chloride. Some insolubles are still visible.

Test 6: Phenolic + naphthalene sulphonic

Note 1: pH=4. 2/3 through tanned, mainly in flesh side. Bath exhausted.

Note 2: pH=4. Through tanned. Bath exhausted. Smooth white grain, less compact and hardest that

test 1. Thickness 3 mm.

Test 7: Tara powder + phenolic + naphthalene sulphonic

Note 1: pH=3.7. 1/3 through tanned (checked with ferric chloride). Some insolubles are

visible.

Note 2: pH=3.8. Through tanned. Some insolubles are visible.

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Photo 4: Design of a pretanning process with tara. Experimental Design I

Photo 5. Light fastness tests. Experimental Design I.

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8.3. Table of tests results and discussions. Design I.

# Description TCºC Tensile

Strength

(N) EN ISO 3376

– IUP6

%

Elongation EN ISO 3376 –

IUP6

Tear load

(N/mm) EN ISO

3377-2,

IUP8

Light

fastness50

1 Tara powder 61.5 551.8 51.6 61.4 4

2 Phenol syntan 68.5 360.0 53.8 57.2 1

3 Naphthalene sulphonic 60.5 461.7 47.7 68.6 2

4 Tara + phenol 63.5 427.3 46.7 58.5 2

5 Tara + naphthalene 68.0 463.7 54.0 53.2 3

6 Phenol + naphthalene 65.5 495.2 48.7 89.0 2

7 Tara+phenol+naphthalene 67.5 477.7 51.8 56.3 2

Table 32: Table o test results. Simplex design with centroids. Experimental design I

With the created experimental design, we have defined 5 statistics variables (TC, Tensile, Elongation,

Tear and Light) for three factors or components (tara, phenol syntan and naphthalene sulphonic), in a

simplex-centroid model, special cubic.

Results are analyzed for each variable in order to obtain the optimal response and the equation of the

fitted model (Statgraphics Plus software).

Shrinking temperature (ST):

Estimated Full Model Effects for ST:

Source P-Value

Mean -

Linear 0.0909

Quadratic 0.0004

Special Cubic -

This table shows the results of fitting different models to the data in ST. The mean model consists of only

a constant. The linear model consists of first-order terms for each of the components. The quadratic

model adds crossproducts between pairs of components. The special cubic model adds terms involving

products of three components. Each model is shown with a P-value which tests whether that model is

statistically significant when compared to the mean square for the term below. It is selected the most

complicated model with a P-value less than 0.05, assuming operating at the 95% confidence level.

50 For the mathematic model, de values of light fastness have been adjusted and the standard criteria have not been considered. The aim is to have a comparison between the trials carried out and not the value of light fastness.

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According to this criterion, it appears that the quadratic model is adequate for the data. The currently

selected model is the quadratic model.

Analysis of variance for ST:

Source Sume of squares Df Mean Square F-Ratio p-Value

Quadratic Model 104.46 5 20.89 109.04 0.0002

Total Error 0.77 4 0.19

Total (corr. 105.22 9

R-squared = 99.27 percent

R-squared (adjusted for d.f.) = 98.36 percent

Standard Error of Est. = 0.44

Mean absolute error = 0.18392

Durbin-Watson statistic = 2.31

Lag 1 residual autocorrelation = -0.16

Since the P-value for this model is less than 0.01, there is a statistically significant relationship between

ST and the components at the 99% confidence level and there is an indication of possible serial

correlation.

Quadratic Model Fitting Results for ST:

Parameter Estimate P-Value

A: Tara 61.5

B: Phenol syntan 68.5

C: Naphthalene sulphonic acid 60.5

AB -4.6 0.0652

AC 29.38 0.0001

BC 5.38 0.0425

The equation of the fitted model, excluding cross-product AB is:

TC = 61.5*Tara + 68.5*Phenol syntan + 60.5*Naphth sulfonic + 29.38*Tara*Naphth sulfonic +

5.38*Phenol syntan*Naphth sulfonic

Figure 29: Estimated response surface for shrinking temperature. Experimental design I

ST

Tara=1,0

Phenol syntan=1,0NaphSulph syntan=1,0

60

62

64

66

68

70

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Optimize Response:

Goal: maximize ST

Optimum value = 68.5ºC

Factor Low High Optimum

Tara 0 1 0

Phenol syntan 0 1 1

Naphthalene sulphonic acid 0 1 0

It is confirmed that phenol condensation tannins increase the shrinking temperatures more than plan

polyphenol gallotannins (Table 11, section 4.2). However, observing the response surface, similar range

of shrinking temperature is obtained with the combination of tara-naphthalene sulphonic syntan. The

synergy can be explained because, despite the low influence on shrinking temperature of the naphthalene

sulphonic syntan, it allows to penetrate tara in the inner layer of the leather, as is appreciate the SEM in

photos 6, 7, 8, and 9.

Tensile strength

Estimated Full Model Effects for Tensile:

Source P-Value

Mean -

Linear 0.0048

Quadratic 0.0006

Special Cubic -

Under the criteria of the estimated Full Model Effects for tensile, it appears that the quadratic Model

Fitting Results is adequate for the data.

Analysis of variance for tensile:

Source Sume of squares Df Mean Square F-Ratio p-Value

Quadratic Model 39,136.9 5 7,827.39 208.45 0.0001

Total Error 150.20 4 37.55

Total (corr. 39,287.1

R-squared = 99.67 percent

R-squared (adjusted for d.f.) = 99.14 percent

Standard Error of Est. = 6.13

Mean absolute error = 2.57

Durbin-Watson statistic = 2.31

Lag 1 residual autocorrelation = -0.16

Since the P-value for this model is less than 0.01, there is a statistically significant relationship between

Tensile and the components at the 99% confidence level and there is an indication of possible serial

correlation.

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Quadratic Model Fitting Results for Tensile:

Parameter Estimate P-Value

A: Tara 551.26

B: Phenol syntan 359.46

C: Naphthalene sulphonic acid 461.16

AB -95.09 0.0207

AC -152.89 0.0040

BC 344.71 0.0002

The equation of the fitted model is:

Tensile = 551.26*Tara + 359.46*Phenol syntan + 461.16*Naphth sulfonic – 95.09*Tara*Phenol syntan –

152.89*Tara*Naphth sulfonic + 344.71*Phenol syntan*Naphth sulfonic

Figure 30: Estimated response surface for tensile strength. Experimental design I

Optimize Response:

Goal: maximize Tensile

Optimum value = 551.26 N

Factor Low High Optimum

Tara 0 1 1

Phenol syntan 0 1 0

Naphthalene sulphonic acid 0 1 0

Pretanning with tara optimizes the values of tensile strength, while the phenolic syntan do not help to

increase this resistance. Combinations of tara and naphthalene sulphonic syntans, as observed in the

estimated response surface, have a range of the highest values. This is confirmed observing SEM in

photos 6, 7, 8 and 9 as fibers keep compacted all through the leather than the other combinations.

Tensile

Tara=1,0

Phenol syntan=1,0 NaphSulph syntan=1,0

350

390

430

470

510

550

590

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Tensile strength elongation:

Estimated Full Model Effects for Elongation:

Under the criteria of the estimated Full Model Effects for elongation, it appears that the quadratic Model

Fitting Results is adequate for the data.

Analysis of variance for elongation:

Source Sume of squares Df Mean Square F-Ratio p-Value

Quadratic Model 67.32 5 13.46 14.92 0.0108

Total Error 3.61 4 0.90

Total (corr. 70.62 3

R-squared = 94.91 percent

R-squared (adjusted for d.f.) = 88.55 percent

Standard Error of Est. = 0.95

Mean absolute error = 0.40

Durbin-Watson statistic = 2.31

Lag 1 residual autocorrelation = -0.16

Since the P-value for this model is near to 0.01, there is a statistically significant relationship between

Tensile and the components at the 95% confidence level and there is an indication of possible serial

correlation.

Quadratic Model Fitting Results for Elongation:

Parameter Estimate P-Value

A: Tara 50.52

B: Phenol syntan 53.72

C: Naphthalene sulphonic acid 47.62

AB -21.01 0.0062

AC 20.39 0.0068

BC -5.51 0.2604

The equation of the fitted model is after excluding cross-product BC:

Elongation = 50.52*Tara + 53.72*Phenol syntan + 47.626*Naphth sulfonic – 21.01*Tara*Phenol syntan

+ 20.39*Tara*Naphth sulfonic

Source P-Value

Mean -

Linear 0.3558

Quadratic 0.0086

Special Cubic -

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Figure 31: Estimated response surface for tensile elongation. Experimental design I

Optimize Response:

Goal: maximize Elongation

Optimum value = 54.85 %

Factor Low High Optimum

Tara 0 1 0.60

Phenol syntan 0 1 0

Naphthalene sulphonic acid 0 1 0.40

Optimal is the combination of tara and naphthalene sulphonic tannin and similar elongation is obtained

with phenol tannin.

Tear load:

Estimated Full Model Effects for Tear:

Under the criteria of the estimated Full Model Effects for tear, it appears that the quadratic Model Fitting

Results is adequate for the data.

Elo

ngation

Tara=1,0

Phenol syntan=1,0 NaphSulph syntan=1,0

47

49

51

53

55

Source P-Value

Mean -

Linear 0.4390

Quadratic 0.0252

Special Cubic -

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Analysis of variance for tear:

Source Sume of squares Df Mean Square F-Ratio p-Value

Quadratic Model 881.23 5 176.25 7.76 0.0347

Total Error 90.87 4 22.72

Total (corr. 972.10 9

R-squared = 90.65 percent

R-squared (adjusted for d.f.) = 79 percent

Standard Error of Est. = 4.77

Mean absolute error = 2.00

Durbin-Watson statistic = 2.31

Lag 1 residual autocorrelation = -0.16

Since the P-value for this model is less than 0.05, there is a statistically significant relationship between

Tear and the components at the 95% confidence level and there is an indication of possible serial

correlation.

Quadratic Model Fitting Results for tear:

Parameter Estimate P-Value

A: Tara 61.82

B: Phenol syntan 57.61

C: Naphthalene sulphonic acid 69.02

AB -18.22 0.4127

AC -62.22 0.0356

BC 89.38 0.0110

The equation of the fitted model is after excluding cross-product AB:

Tear = 61.82*Tara + 57.61*Phenol syntan + 69.02*Naphth sulfonic – 62.22*Tara*Naphth sulfonic +

89.38 Phenol syntan*Naphth sulfonic

Figure 32: Estimated response surface for tensile elongation. Experimental design I

Tear

Tara=1,0

Phenol syntan=1,0 NaphSulph syntan=1,0

49

59

69

79

89

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Optimize Response:

Goal: maximize Tear

Optimum value = 86.03 N/mm

Factor Low High Optimum

Tara 0 1 0

Phenol syntan 0 1 0.40

Naphthalene sulphonic acid 0 1 0.60

Light fastness

Estimated Full Model Effects for lightfastness:

Under the criteria of the estimated Full Model Effects for tear, it appears that the quadratic Model Fitting

Results is adequate for the data.

Analysis of variance for tear:

Source Sume of squares Df Mean Square F-Ratio p-Value

Quadratic Model 10.03 5 2.01 116.36 0.0002

Total Error 0.67 4 0.02

Total (corr. 10.10

R-squared = 99.32 percent

R-squared (adjusted for d.f.) = 98.46 percent

Standard Error of Est. = 0.13

Mean absolute error = 0.06

Durbin-Watson statistic = 2.31

Lag 1 residual autocorrelation = -0.16

Since the P-value for this model is less than 0.01, there is a statistically significant relationship between

Lightfastness and the components at the 99% confidence level and there is an indication of possible serial

correlation.

Quadratic Model Fitting Results for lightfastness:

Parameter Estimate P-Value

A: Tara 4.01

B: Phenol syntan 1.01

C: Naphthalene sulphonic acid 2.01

AB -2.41 0.0118

AC -0.41 0.4934

BC 1.59 0.0447

Source P-Value

Mean -

Linear -

Quadratic 0.0288

Special Cubic -

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The equation of the fitted model is after excluding cross-product AC:

Lightfastness = 4.012*Tara + 1.01*Phenol syntan + 2.01*Naphth sulfonic –0.41*Tara*Phenol syntan +

Phenol syntan*Naphth sulfonic

Figure 33: Estimated response surface for lightfastness. Experimental design I

Optimize Response:

Goal: maximize lightfastness

Optimum value = 4.01

Factor Low High Optimum

Tara 0 1 1

Phenol syntan 0 1 0

Naphthalene sulphonic acid 0 1 0

Tara itself has gives good light fastness to the leather, as we have already commented in section 2.4. It is

well know the use of tara in the automobile industry. It is required in interior materials able to maintain its

properties under extreme expositions. Combinations with naphthalene sulphonic syntan have a lower

negative influence in the light fastness values than the phenol condensation syntan.

8.4. Conclusions of the Experimental Design I

There is a variety of results and the optimization of the mixtures will depend of the variables we analyze:

a) Shrinking temperature is optimized when using a phenolic syntan but similar result is obtained

blending tara powder and naphthalene sulphonic syntan.

b) Tensile strength is optimized when using tara powder and its combinations with syntans has a

negative effect. Naphthalene sulphonic syntan lower effect in tensile strength blending tara

powder is less than the blend of tara powder with phenolic syntan.

c) Elongation is optimized when using a phenolic syntan but similar result is obtained blending tara

powder and naphthalene sulphonic syntan.

Lig

htf

ast

ness

Tara=1,0

Phenol syntan=1,0NaphSulph syntan=1,0

1

2

3

4

5

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d) Tear load is optimized by combining phenolic and naphthalene sulphonic syntans. Blends with

tara do not improve tear load.

e) Lightfastness is optimized when using tara powder and its combinations with syntans has a

negative effect. Naphthalene sulphonic syntan lower effect in lightfastness blending tara powder

is less than the blend of tara powder with phenolic syntan.

It can be observed that tara powder has, in general, good properties because its tanning effect, but in most

of the cases, it is not optimal because, due to its astringency, it has certain limits to penetrate inside the

leather.

With the help of an auxiliary syntan, naphthalene sulphonic type, penetration is improved considerably

and the behavior of their combinations are able to obtain similar or even better values than a replacement

syntan, phenol condensation type. This thesis is supported also, with the following SEM photographs:

Photo 6: SEM photo. Tara. 24x & 202x

The leather is well tanned on surface, while the inner layer fibers are open and well differentiated. The

rapid superficial tanning effect of tara, due to its astringency, does not allows the unreacted tannins to

penetrate inside the leather.

Photo 7: SEM photo. Tara + Naphthalene sulphonic syntan. 24x & 202x

The fibers are very compacted and they are not differentiated due to the crosslinking effect of the tannins.

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Photo 8: SEM photo. Tara + phenol condensation syntan. 24x & 202x

Fibbers are very compacted and tanning is obtained all through the leather. Especially in the grain layer,

fibbers have disappeared and material is tight and hom*ogeneous.

Photo 9: SEM photo. Tara + Naphth. sulphonic syntan + phenol condensation syntan. 24x & 202x

Fibers are visible and there is certain uniformity among the grain and the inner layers.

Differences between the tests are remarkable and the behavior of the leather depends much more of the

variables than the combination of products.

Considering the goals of the work, using tara as sustainable tanning agent, we observe that, further the

test where tara alone has the best results (light fastness and tensile strength), good results and comparable

to the ones achieved with the phenol condensation syntan, are the combinations of tara tannin and the

naphthalene sulphonic syntan acting as tanning auxiliary. In these cases, a certain synergy is observed

(Tensile elongation).

We assume that this combination (tara + naphthalene sulphonic syntan) will enhance the performance of

the tara tannins what is the aim of this resaerch.

The chosen experimental design has only determined a mixture of equal proportions of the ingredients,

calculated on the tanning content.

The second experimental design will analyzed different percentages of the two products to define the

most appropriate recipe for a sustainable wet white formulation.

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9. Pretanning process with tara. Experimental design II: Optimizing

with naphthalene sulphonic syntan.

Pretanning process with tara, part I, aims obtaining the components of a mixture that better fits tara by

improving its performance for a sustainable wet white pretanning process. Combining tara powder with a

naphthalene sulphonic syntan was selected. This part 2 optimizes the best blend composition of the two

ingredients to maximize the values of shrinking temperature, tensile strength, tensile elongation and tear

resistance.

9.1. Products, materials and equipment. Experimental design II.

To carry out the experimental tests, the following commercial products were selected:

Synthetic tanning of naphthalene sulphonic:

Yellowish liquid. Miscible in water. 40 % of tannin content. pH 3.3 – 3.7 (solution 1:10)

Tara Powder: Origen: Peru

Quality Control pH 3.5 Insolubles 32 %

Tannin content 47 % Soluble solids 60 %

Non tannin content 13 % Total solids 92 %

Water 8 % Iron 388.9 mg/kg

(ppm) by atomic

absorbance

Figure 34: Sampling hides for testing. Experimental design II

1

76

1613

129

85

432

1514

1110

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The trials were carried out using the following drums:

Pretanning process:

2 – Simplex drums, stainless steel, 4 T.D.F. Annex 10.

9.2. Tests to optimize ratios with naphthalene sulphonic syntan. Experimental design II.

To obtain comparative tests, it was used Russian bovine hides, green split. They were divided in 16 pieces

and marked (Figure 34). The sixteen pieces were weight and their thicknesses were calibrated.

Deliming, bating and pickling treatment were carried out according the recipe of table 30.

Trials were carried out according to the recipe of table 33. The percentages of the pretanning commercial

agents were adjusted to their tannin content according to the same calculation as in design I.

Table 33: Recipe for pretanning. Experimental design II

To optimize a magnitude that depends from one o more variables X = (x, y, …z), it is necessary to

determine the values of the parameters which the function obtains the absolute optimal, maximal or

minimal values.

There exists several techniques to optimize a function, but to simplify and better understand the behavior

of the blend, the experiments will be based on a design with a response surface. Visually, best fitted

response can be analyzed in a certain area of interest factor levels and the sensibility to the factors can be

evaluated.

The response surface and the analysis strategy will assume that the average of the response variable µy is

a function of the quantitative factor levels represented by the variables x1, x2, …, xk. The polynomials

models are used in the practice to estimate the real function. Normally, the real function is unknown and

polynomial function often gives a good loom in areas relatively small of the quantitative factor levels.

Operation % Product T oC Running time Control

Conditioning 50 Water 20

4 Sodium chloride

10 min.oBè=6

Add hides to drum 10 min.

Pretanning 50 Water 20

A Tara powder

B Naphthalene sulphonic syntan liquid Overnight

2,0 Fatliquor 2 hours

0,5 Formic acid 85% 120 min.

Drain

Washing 300 Water 20 20 min.

Drain

Horse up. Samming. Pasting 12 hours at 30ºC. Conditioning and stake.

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The polynomial models used to analyze variable response surfaces are normally lineal:

µy = β0 + β1x1 + β2x2

or quadratic:

µy = β0 + β1x1 + β2x2 + β11x12 + β22x2

2 + β12x1x2

When the optimal surface region is identified, a new design is necessary to characterize the variable

response surface. 2k factorial models are useful designs to identify significant factors and optimal

response regions but require a big number of tests.

Box and Wilson (1951) proposed decentralized designs reducing the number of combinations, based on 2n

factorials with 2n additional combinations, or axial points, through the coordinated axis of codified factor

levels: (±α,0,0,…,0),(0,±α,0,…0),…(0,0,0…±α) and m replications in the designed center of the

coordinates.

In order to obtain the same accuracy for all the mean estimations, it is necessary a rotatable design. In this

case, the accuracy of the estimated surface is independent of the design orientation with regard to the real

response.

Centralized design becomes rotatable establishing axial points values a α = (2n)

1/4.

The α value for a 2 factor design is:

α = (4)1/4

= 2 = 1,414

The surface graphic for a quadratic, centralized, orthogonal and rotatable design is in Figure 35.

Figure 35: Quadratic, centralized, orthogonal and rotatable design

Limits (V1,414, V-1,414) of independent variable % tara powder and % naphthalene sulphonic syntan are

based on previous experiences and technical information from chemical suppliers. % tara powder shall

x2

+2

+2-2

-2

(1,1)

(0,0)

(0,1.414)

(-1,1)

(-1,-1)(1,-1)

(-1.414,0) (1.414,0)

(0,-1.414)

.

.

.

.

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range between 0 and 12% while % Naphthalene sulphonic syntan between 0 and 14%. The values on

coordinates 1 and -1, V1 and V-1 are calculated proportionally.

If V0 is the value of the variable to the origin and V1,414 and V-1,414 the performance limits of the ranges of

the variables:

V0 = (V1,414+V-1.414)/2

(x+1.414)/1.414= (Vx-V-1.414)/(V0-V-1.414) → Vx = (V0-V-1.414)(x+1.414)/1.414+V-1.414

Replacing the values for tara powder:

V1,414= 12 % tara powder i V-1.414=0% tara powder

V0= (12 + 0)/2= 6 % tara powder

V1= (6-0) (1+1.414)/1.414+0 = 10,2 %

V-1 = (6-0) (-1+1.414)/1.414+0 = 1,76 %

Replacing the values for naphthalene sulphonic syntan:

V0 = (14+0)/2=7% naphthalene sulphonic syntan

V1= (7-0) (1+1.414)/1.414+0 = 12 %

V-1 = (7-0) (-1+1.414)/1.414+0 = 2 %

Experimental independent variables: % of tara powder and % Naphthalene sulphonic syntan added to the

pre-tanning process according application recipe of table 34.

Test x1 x2 % Tara powder % Naphthalene

sulphonic syntan

1 -1 -1 1.8 2

2 -1 1 1.8 12

3 1 -1 10.2 2

4 1 1 10.2 12

5 0 -1.414 6 0

6 0 1.414 6 14

7 -1.414 0 0 7

8 1.414 0 12 7

9 0 0 6 7

10 0 0 6 7

11 0 0 6 7

12 0 0 6 7

13 0 0 6 7

Table 34: Quadratic, centralized, rotatable and orthogonal design for tara and naphthalene sulphonic syntan. Codification table.

Experimental design II.

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Photo 10 shows the leather pieces test results in the coordinates according the described experimental

design:

Photo 10: Optimization for a pretanning process with tara. Experimental design II.

Table 35: includes the physical test results to be statistically analyzed:

Test Coordinates TCºC Tensile

Strength

(N) EN ISO 3376-

IUP6

%

Elongation EN ISO 3376-

IUP6

Tear load

(N/mm) EN ISO 3377-

2 IUP8

Lightfastness

1 (-1, -1) 61 743.0 49.0 76.9 2

2 (-1, 1) 69 725.3 44.1 79.5 2

3 (1, -1) 59 777.3 38.1 65.5 3

4 (1, 1) 71 709.5 39.5 64.3 3

5 (0, -1.414) 63 848.0 38.9 68.1 3

6 (0, 1.414) 74 900.5 37.0 72.3 1

7 (-1.414, 0) 63 875.0 52.8 81.9 1

8 (1.414, 0) 70 1022.0 48.4 82.8 4

9 (0, 0) 65 903.0 44.7 82.3 2

10 (0, 0) 65 903.0 44.7 82.3 2

11 (0, 0) 65 903.0 44.7 82.3 2

12 (0, 0) 65 903.0 44.7 82.3 2

13 (0, 0) 65 903.0 44.7 82.3 2

Table 35: Test results from experimental design II

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Photo 11: Light fastness test. Experimental design II

9.3. Test results and discussion. Experimental design II:

Results are analyzed for each variable in order to obtain the optimal response for each variable:

Shrinking temperature (ST oC):

Estimated effects for ST

average 65.00 +/- 0.88

A:Tara 2.47 +/- 1.39

B:Syntan 8.89 +/- 1.39

AA 0.25 +/- 1.50

AB 2.00 +/- 2.00

BB 2.25 +/- 1.50

Analysis of Variance for ST

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 12.25 1 12.25 3.15 0.1192

B:Syntan 158.03 1 158.03 40.64 0.0004

AA 0.11 1 0.11 0.03 0.8719

AB 4.00 1 4.00 1.03 0.3442

BB 8.80 1 8.80 2.26 0.1761

Total error 27.22 7 3.89

The ANOVA table partitions the variability in ST into separate pieces for each of the effects. It then tests

the statistical significance of each effect by comparing the mean square against an estimate of the

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experimental error. In this case, % syntan has P-values less than 0.05, indicating that they are

significantly different from zero at the 95.0% confidence level.

Figure 36: Pareto chart for shrinking temperature. Experimental design II

Since the effect of the % of syntan has statistical significance to the variable shrinking temperature at

95% confidence, we conclude that there is a correlation between the shrinking temperature and the % of

syntan according the following lineal equation:

ST = 65.77 + 4.44*Syntan

Figure 37: Lineal correlation ST and % syntan. Experimental design II.

Despite the variable responses tara cannot be statistically proved within the mathematical at 95%

confidence, figure 38 illustrates tendencies of shrinking temperature responses for effects % tara and %

syntan, excluding the other cross-products.

Standardized Pareto Chart for ST

0 2 4 6 8

Standardized effect

AA

AB

BB

A:Tara

B:Syntan +-

Main Effects Plot for ST

ST

Syntan-1,0 1,0

61,3247

70,2138

1,0

61

63

65

67

69

71

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Figure 38: Estimated Response Surface for shrinking temperature. Experimental design II

Optimize Response:

Goal: maximize Shrinking temperature

Optimum value: 73.80ºC

Factor Low High Optimum

Tara -1.414 1.414 1.414

Syntan -1.414 1.414 1.414

Tensile strength (N)

Estimated effects for Tensile

average 903.00 +/- 43.84

A:Tara 56.60 +/- 69.31

B:Syntan -2.81 +/- 69.31

AA -40.80 +/- 74.33

AB -25.05 +/- 98.02

BB -115.05 +/- 74.33

TaraSyntan

ST

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

60

62

64

66

68

70

72

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Analysis of Variance for ST

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 6406.51 1 6406.51 0.67 0.4411

B:Syntan 15.83 1 15.83 0.00 0.9688

AA 2895.09 1 2895.09 0.30 0.6001

AB 627.50 1 627.50 0.07 0.8056

BB 23020.20 1 23020.20 2.40 0.1650

Total error 67254.70 7 9607.81

Total (corr.) 98501.90 12

None of the effects have P-values less than 0.05, indicating that they are not statically significant at the

95.0% confidence level.

Figure 39: Pareto chart for tensile strength. Experimental desing II

Despite statistically significant effects have not been found, estimated response surface considers

interaction of syntan (BB) and % of tara to have an idea of a tendency and to draw a conclusion about.

Tensile = 903 + 28.30*Tara – 1.41*Syntan – 20.40 * (Tara)2 – 12.53 * Syntan – 57.53*(Syntan)

2

Standardized Pareto Chart for Tensile

0 0,4 0,8 1,2 1,6 2 2,4

Standardized effect

B:Syntan

AB

AA

A:Tara

BB +-

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Figure 40: Estimated response surface for Tensile. Experimental design II

Optimize Response:

Goal: maximize Tensile

Optimum value: 913.27 N

Factor Low High Optimum

Tara -1.414 1.414 1.414

Syntan -1.414 1.414 0.000

Tensile elongation (%)

Estimated effects for Tensile

average 44.70 +/- 0.89

A:Tara -6.66 +/- 1.40

B:Syntan -0.32 +/- 1.40

AA 5.71 +/- 1.50

AB 0.70 +/- 1.98

BB -6.94 +/- 1.50

Analysis of Variance for Elongation

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 88.60 1 88.60 22.56 0.0021

B:Syntan 0.21 1 0.21 0.05 0.8250

AA 56.75 1 56.75 14.45 0.0067

AB 0.49 1 0.49 0.12 0.7343

BB 83.70 1 83.70 21.31 0.0024

Total error 27.49 7 3.93

Total (corr.) 277.96 12

TaraSyntan

Tensile

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

800

820

840

860

880

900

920

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For % elongation, 3 effects, % of tara and the quadratic effects of % tara and % of tannin have P-values

less than 0.05, indicating that they are significant at the 95.0% confidence level.

Figure 41: Pareto chart for tensile elongation. Experimental design II

After excluding the effects AB and B with no statistic significance, we drew the estimated response

surface and optimize response.

Elongation = 44.7- 3.33*Tara + 2.86*(Tara)2 – 3.47 (Syntan)

2

Figure 42: Estimated response surface for tensile elongation. Experimental design II

Optimize Response:

Goal: maximize Elongation

Optimum value: 55.12%

Factor Low High Optimum

Tara -1.414 1.414 -1.414

Syntan -1.414 1.414 0

Standardized Pareto Chart for Elongation

0 1 2 3 4 5

Standardized effect

B:Syntan

AB

AA

BB

A:Tara +-

TaraSyntan

Elo

ngation

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

40

42

44

46

48

50

52

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Tear load (N/mm)

Estimated effects for tear load

average 82.30 +/- 2.03

A:Tara -5.68 +/- 3.21

B:Syntan 1.18 +/- 3.21

AA -2.64 +/- 3.44

AB -0.60 +/- 4.54

BB -14.7+ +/- 3.44

Analysis of Variance for Tear

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 64.57 1 64.57 3.14 0.1197

B:Syntan 2.81 1 2.81 0.14 0.7227

AA 12.10 1 12.10 0.59 0.4682

AB 0.63 1 063 0.02 0.8985

BB 380.30 1 380.30 18.49 0.0038

Total error 143.99 7 20.57

Total (corr.) 592.91 12

For tear load, the quadratic effec of syntan has P-values less than 0.05, indicating that they are significant

at the 95.0% confidence level.

Figure 43: Pareto chart for tear load. Experimental design II

After excluding the effects with no statistic significance, AA, B and AB, we drew the estimated response

surface and optimize response.

Tear = 81.38 – 2.84*Tara – 7.22 (Syntan)2

Standardized Pareto Chart for Tear

0 1 2 3 4 5

Standardized effect

AB

B:Syntan

AA

A:Tara

BB +-

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Figure 44: Estimated response surface for tear load. Experimental design II

Optimize Response:

Goal: maximize Tear load

Optimum value: 81.38 N/mm

Factor Low High Optimum

Tara -1.414 1.414 0.0

Syntan -1.414 1.414 0.0

Lightfastness

Estimated effects for lightfastness

average 3,20 +/- 0,43

A:Tara 1,56 +/- 0,68

B:Syntan -0,71 +/- 0,68

AA -0,58 +/- 0,73

AB -0,00 +/- 0,97

BB -1,07+ +/- 0,73

Analysis of Variance for Lightfastness

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 4.87 1 4.87 5.20 0.0566

B:Syntan 1.00 1 1.00 1.07 0.3358

AA 0.57 1 0.57 0.61 0.4589

AB 0.00 1 0.00 0.00 1.0000

BB 2.00 1 2.00 2.15 0.1863

Total error 6.55 7 0.94

Total (corr.) 14.77 12

TaraSyntan

Tear

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

71

74

77

80

83

86

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Figure 45: Pareto chart for lightfastness. Experimental design II

When excluding all effects except % of tara, the following analysis of variance is obtained:

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:Tara 4.87 1 4.87 5.41 0.0401

Total error 9.90 11 0.90

Total (corr.) 14.75 12

Effect tara has P-value less than 0.05, indicating that it is significant at the 95.0% confidence level.

In this case, regression coefficients were calculated to obtain the equation of the fitted model:

Lightfastness = 2,69 + 0,78*Tara

Figure 46: Linea correlation lightfastness and % tara. Experimental design II

Standardized Pareto Chart for Lightfastness

0 0,4 0,8 1,2 1,6 2 2,4

Standardized effect

AB

AA

B:Syntan

BB

A:Tara +-

Main Effects Plot for Lightfastness

Lig

htf

ast

ness

Tara-1,0 1,0

1,91198

3,47264

1,9

2,3

2,7

3,1

3,5

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Optimize Response:

Goal: maximize lightfastness

Optimum value: 3.80

Factor Low High Optimum

Tara -1,414 1,414 1,414

Syntan -1,414 1,414 0,0

9.4 Conclusions of the Experimental Design II

The values of the statistic results indicate the influence of the effects of % naphthalene sulphonic syntan

with % tara powder to the response variables of shrinking temperature, tensile strength, tensile elongation,

tear load and lightfastness.

The amount of tara in the recipe has very little influence on the shrinking temperature but this can be

considerably improved with the help of the auxiliary syntan and confirming, at the same time, the results

of the experimental design I. This can be checked with the SEM microscopy photos (photos 6 and 7) and

can be implicit to the improvement of the penetration of the tara powder allowing the cross linking with

the inner fiber of the collagen structure. The correlation is calculated and expressed with a lineal equation

valid for the area of the analysis.

Optimization for tensile strength cannot be proposed as the tests do not prove a significance correlation

between this response variable and the effects of the factors % of tara and % of syntan. By observing the

estimated response surface the naphthalene sulphonic has an irrelevant negative effect on this variable

from the statistical analysis.

With regard to the tensile elongation, the % of tara has a negative effect what is a general characteristic of

vegetable tannins when compare with chrome tanning. Improvement with naphthalene sulphonic syntan

has not been statistically validated. Observing estimated response surface, the graphic shows that % of

tara and % of syntan is optimized when concentrations are similar.

Similar results are obtained for variable response tear load. % of tara has a negative effect and the

naphthalene sulphonic syntan optimal responses are observed along the coordinate axis.

Tests on lightfastness also confirm that tara tannins are appreciated because this property. Naphthalene

sulphonic syntan may have a negative effect but results do not demonstrate a statistical significance

effect. Table 36 summarizes these general tendencies:

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Variable responses

Effect of the factor Influence of the

syntan to the effect

of the tara powder % Tara poder

% Naphthalene

sulphonic syntan

Shrinking temperatura + ++ ++

Tensile strength + () ()

Tensile elongation -- () +

Tear load - + +

Lightfastness ++ - -

Table 36: Conclusions effects of tara and syntan on wet-white properties

Legend: ++ Very positive

+ Positive

() No influence

- Very negative

- Negative

Optimal values for Syntan Tara

Shrinking temperature 1,41 1,41

Tensile strength 1.41 0.00

Tensile elongation -1.41 0.00

Tear loan 0.00 0.00

Light fastness 1.41 0.00

Mean 1.41 0.00

Average 0.57 0,28

Table 37: Optimal values syntan and tara

The values in table 37 values will be considered according to the requirements of the final article to be

manufactured with the subsequent processes of retanning, fatliquoring, dyeing and finishing.

Shrinking temperature needs to be maximized to ensure heat resistance to the mechanical treatments after

pretanning, mainly shaving, to obtain appropriate and regular thickness among the different parts of the

hides or skins.

The physical properties will depend on the quality requirements of the goods manufactured with the

leather article. While tear load is an important property for apparel, elongation is fundamental for the

manufacture of shoes where leather is exposed to high tensile forces.

In general, however, all these physical properties considered in this research are common for most of the

leather articles produced for the shoe, apparel, upholstery and leather good markets, thus the mean of all

these coordinate values is considered as the most balanced value.

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Considering the means of the values for optimize response of table 37, the summary from table 36 and

proposing to maximize the use of tara tannins as a main component for a sustainable pre-tanning agent,

we conclude that optimal values for the ingredients of a mixture of tara powder and a naphthalene

sulphonic syntan as:

1.41 tara powder + 0 Naphthalene sulphonic syntan

According to the formulas for Codification Table, Design II, table 34:

Coordinate value tara tannin [x1] = Me [ST, Tens, Elon, Tear] = 1.41

% tara powder = 12 %

Coordinate value naphthalene sulphonic syntan [x2] = Me [ST, Tens, Elon, Tear] = 0.00

% naphthalene sulphonic syntan = 7 %

12 % Tara powder

7 % Naphthalene sulphonic syntan

When comparing the concentration of tannins of the commercial samples of tara powder and the

naphthalene sulphonic syntan used for the experiments, the calculated ratios are:

12 x 0.47 % of tara tannins = 5.64 → 67%

7 x 0.40 % of naphthalene sulphonic tannins = 2.80 → 33%

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10. Pretanning process with tara. Experimental design III: Optimizing

pre-tanning pelt and final pH conditions.

10.1. Tests to optimize pretanning process. Design III.

Design of a pretanning process with tara, design III, aims to identify the most appropriate conditions, by

means, optimal pH before and after the wet white pretanning process that better enhance selected physical

properties. This design III optimizes the best working conditions of pH for the application of the blend of

tara tannin and naphthalene sulphonic syntan obtained in design II maximizing the values of shrinking

temperature, tensile strength, tensile elongation and tear resistance.

The tests were carried out according to the application formula in table 38:

Table 38: Application formula for wet-white. Experimental design III

To optimize the magnitude that depends from the variables X=(Ts, Tens, Elon, Tear, Light), according to

Table 39, it is necessary to determine the values of the parameters, % of sodium formate and % of

formic acid 85%, which the function obtains the absolute optimal, maximal or minimal values.

Ts Temperature of shrinkage ºC

Tens Tensile strength N EN ISO 3376-IUP6

Elon Elongation % EN ISO 3376-IUP6

Tear Tear load N/mm EN ISO 3377-2 IUP8

Table 39: Variables for Experimental design III

Operation % Product T oC Running time Control

Conditioning 50 Water 20

4 Sodium chloride

10 min.oBè=6

Add hides to drum 10 min. pH= 3.3

Depickling A Sodium formate

A/2 Sodium bicarbonate 120 min. pH=

Drain

Pretanning 50 Water 20

12 Tara powder

7 Naphthalene sulphonic syntan liquid Overnight

2 Fatliquor

B Formic acid 85% 120 min. pH=

Drain

Washing 300 Water 20 20 min.

Drain

Horse up. Samming. Pasting 12 hours at 30ºC. Conditioning and stake.

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The experiments were based on a design with a response surface. The mathematic model has been

described in 9.2.

Visually, best fitted response can be analyzed in a certain area of interest factor levels and the sensibility

to the factors can be evaluated. The % of sodium formate and % of formic acid 85% were calculated

according to a quadratic, centralized, orthogonal and rotatable design as summarized in table 40.

Limits of % sodium formate and % of formic acid 85% are based on previous experiences. Depickling

shall range between the pickling pH (no addition of neutralizing salts) to pH of approximately 5-5.5,

approximately the isoelectric point of the collagen. See figure 1.3.

In order to fix the anionic tannins on the collagen substrate it is necessary to reduce pH, lower than its

isoelectric point. Range is fixed between 0.2 to 1%.

The values on coordinates 1 and -1, V1 and V-1 are calculated proportionally.

If V0 is the value of the variable to the origin and V1.414 and V-1.414 the performance limits of the ranges of

the variables:

V0 = (V1.414+V-1.414)/2

(x+1.414)/1.414= (Vx-V-1.414)/(V0-V-1.414) → Vx = (V0-V-1.414)(x+1.414)/1.414+V-1.414

Replacing the values:

Depickling:

V1.414= 1% de NaCOOH i V-1.414=0% de NaCOOH

V0= (1 + 0)/2= 0.5% de NaCOOH

V1= (0.5-0) (1+1.414)/1.414+0 = 0,85 %

V-1 = (0.5-0) (-1+1.414)/1.414+0 = 0,15%

Fixing:

V0=(1+0.2)/2=0.6% de HCOOH

V1= (0.6-0.2) (1+1.414)/1.414+0,2 = 0.88 %

V-1 = (0.6-0.2) (-1+1.414)/1.414+0,2 = 0.32%

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Test x1 x2 % Sodium formate % Formic acid 85%

1 -1 -1 0.15 0.32

2 -1 1 0.15 0.88

3 1 -1 0.85 0.32

4 1 1 0.85 0.88

5 0 -1.414 0.5 0.2

6 0 1.414 0.5 1

7 -1.414 0 0 0.6

8 1.414 0 1 0.6

9 0 0 0.5 0.6

10 0 0 0.5 0.6

11 0 0 0.5 0.6

12 0 0 0.5 0.6

13 0 0 0.5 0.6

Table 40 Quadratic, centralized, rotatable and orthogonal design for % sodium formate and % formic acid 85%. Codification

table. Experimental design III

10.2. Test results and discussions. Experimental design III:

Photo 12 shows the leather pieces test results in the coordinates according the described experimental

design:

Photo 12: Optimizing for a pretanning process with tara. Experimental design III.

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10.2.1 % NaCOOH vs. initial wet-white process pH

Since conditioning of pre-tanning depends of the pH of the pelts, the pH obtained after the treatment with

sodium formate and sodium bicarbonate were recorded in table 41:

% NaCOOH 0 0 0.15 0.15 0.5 0.5 0.85 0.85 1 1

pH 3.3 3.3 3.53 3.55 4.4 4.5 4.87 4.91 6.5 6.5

Table 41: pH vs % NaCOOH. Experimental design III.

Analysis of Variance

Source Sum of Squares Df Mean Square F-Ratio P-Value

Between groups 13.0194 4 3.25486 2712.38 0.0000

Within groups 0.006 5 0.0012

Total (Corr.) 13.0254 9

The ANOVA table decomposes the variance of pH into two components: a between-group component

and a within-group component. The F-ratio, which in this case equals 2712.38, is a ratio of the between-

group estimate to the within-group estimate. Since the P-value of the F-test is less than 0.05, there is a

statistically significant difference between the mean pH from one level of NaCOOH to another at the

95,0% confidence level.

Multiple Regression Analysis

Dependent variable: pH

Parameter Estimate Standard Error T Statistic P-Value

CONSTANT 3.1451 0.,2237 14.0613 0.0000

NaCOOH 2.7819 0.3541 7.85635 0.0000

Analysis of Variance

Source Sum of

Squares

Df Mean Square F-Ratio P-Value

Model 11.5309 1 11.5309 61.72 0.0000

Residual 1.4945 8 0.1868

Total (Corr.) 13.0254 9

R-squared = 88.5259 percent

R-squared (adjusted for d.f.) = 87.0916 percent

Standard Error of Est. = 0.4322

Mean absolute error = 0.2912

Durbin-Watson statistic = 1.2057 (P=0.0315)

Lag 1 residual autocorrelation = 0.2792

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The output shows the results of fitting a multiple linear regression model to describe the relationship

between pH and 1independent variables. The equation of the fitted model is

pH = 3.15 + 2.78*NaCOOH

Since the P-value in the ANOVA table is less than 0.01, there is a statistically significant relationship

between the variables at the 99% confidence level.

The R-Squared statistic indicates that the model as fitted explains 88.53% of the variability in pH. The

adjusted R-squared statistic, which is more suitable for comparing models with different numbers of

independent variables, is 87.09%. The standard error of the estimate shows the standard deviation of the

residuals to be 0.43. This value can be used to construct prediction limits for new observations.

The mean absolute error (MAE) of 0.29 is the average value of the residuals. The Durbin-Watson (DW)

statistic tests the residuals to determine if there is any significant correlation based on the order in which

they occur in the data file. Since the P-value is less than 0.05, there is an indication of possible serial

correlation. Plot the residuals versus row order to see if there is any pattern which can be seen.

In determining whether the model can be simplified, notice that the highest P-value on the independent

variables is 0.0000, belonging to NaCOOH. Since the P-value is less than 0.01, the highest order term is

statistically significant at the 99% confidence level.

Table 42: Fitted model for pH vs. NaCOOH. Experimental design III

Plot of Fitted Model

0 0,2 0,4 0,6 0,8 1

NaCOOH

3,3

4,3

5,3

6,3

7,3

pH

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10.2.2 % NaCOOH and % HCOOH vs. final wet-white process pH

This second statistic analysis determines the influence of %NaCOOH and %HCOOH to the final pH. The

aim is to ensure the quality of the data and validate the factors prior to final analysis and conclusions.

The results obtained in the experimental design were recorded in Table 43:

1 2 3 4 5 6 7 8 9

%NaCOOH 0.15 0.15 0.85 0.85 0.5 0.5 0 1 0.5

%HCOOH 0.32 0.88 0.32 0.88 0.2 1 0.6 0.6 0.6

Final pH 3.4 3.1 4 3.6 3.9 3.5 3 4 3.6

Table 43: % NaCOOH and %HCOOH vs. final pH. Experimental design III.

Analysis of Variance for Final pH

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:% NaCOOH 0.7902 1 0.7902 47.64 0.0000

B:% HCOOH 0.2002 1 0.2002 12.07 0.0060

AA 0.0703 1 0.0703 4.24 0.0665

AB 0.0025 1 0.0025 0.15 0.7060

BB 0.0003 1 0.0003 0.02 0.8935

Total error 0.1658 10 0.0166

Total (corr.) 1.,2294 15

R-squared = 86.5097 percent

R-squared (adjusted for d.f.) = 79.7645 percent

Standard Error of Est. = 0.1288

Mean absolute error = 0.0671

Durbin-Watson statistic = 1.9775 (P=0.4439)

Lag 1 residual autocorrelation = -0.0158

The ANOVA table partitions the variability in Final pH into separate pieces for each of the effects. It then

tests the statistical significance of each effect by comparing the mean square against an estimate of the

experimental error. In this case, 2 effects have P-values less than 0.05, indicating that they are significant

at the 95.0% confidence level.

The R-Squared statistic indicates that the model as fitted explains 86.5097% of the variability in Final pH.

The adjusted R-squared statistic, which is more suitable for comparing models with different numbers of

independent variables, is 79.7645%. The standard error of the estimate shows the standard deviation of

the residuals to be 0.1288. The mean absolute error (MAE) of 0.0671 is the average value of the

residuals. The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant

correlation based on the order in which they occur in your data file. Since the P-value is greater than

0.05, there is no indication of serial autocorrelation in the residuals.

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Figure 47: Standardized Pareto Chart for Final pH. Experimental design III

Considereing the significant effects, % HCOOH and % NaCOOH, as well as the quadratic effect of %

NaCOOH (P-value higher that 0.05 when excluding other effects), estimated surfacer response is drawn

in figure 48.

Figure 48: Estimated response surface Final pH vs. %NaCOOH and HCOOH

Regression coeffs. for Final pH

constant = 3.65

A:% NaCOOH = 0.31

B:% HCOOH = -0.16

AA = -0.19

Standardized Pareto Chart for Final pH

0 2 4 6 8

Standardized effect

BB

AB

AA

B:% HCOOH

A:% NaCOOH +-

% NaCOOH% HCOOH

Fin

al pH

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

3

3,2

3,4

3,6

3,8

4

4,2

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This pane displays the regression equation which has been fitted to the data. The equation of the fitted

model is

Final pH = 3.65 + 0.31*% NaCOOH – 0.16*% HCOOH – 0.19*(%NaCOOH)2

where the values of the variables are specified in their original units.

Photos 13 and 14 show the exhaustion baths after pretanning operation for each of the tests carried out

according to design II.

The lowest part demonstrate the fraction of insolubles that were not introduced into the protein structure

during the pretanning operation, while the top is a cleaner liquor which intensity of color demonstrate the

portion of tannins that bond with the reactive groups of the collagen. See table 10 from section 4.1.

Photo 13: Exhaustion baths I. Experimental design III.

Photo 14: Exhaustion baths II. Experimental design III.

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10.3 Results and discussions. Experimental design III

Table 44: includes the physical test results to be statistically analyzed:

Test Coordinates ST

(oC)

Tensile Strength

(N)

EN ISO 3376-IUP6

Elongation

(mm)

EN ISO 3376-IUP6

Tear load

(N/mm)

EN ISO 3377-2 IUP8

1 (-1, -1) 67 626.0 36 127

2 (-1, 1) 69 543.0 46 141

3 (1, -1) 67 549.0 48 144

4 (1, 1) 71 574.0 48 118

5 (0, -1.414) 67 468.0 43 98

6 (0, 1.414) 69 499.0 39 116

7 (-1.414, 0) 63 507.0 42 140

8 (1.414, 0) 68 370.0 52 129

9 (0, 0) 63 601.0 43 89

Table 44: Test results from experimental design III

Results for shrinking temperature (ST)

Analysis of Variance for ST

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:NaCOH 10.2855 1 10.2850 9.71 0.0110

B:HCOOH 9.74265 1 9.7426 9.19 0.0126

AA 22.7812 1 22.7812 21.50 0.0009

AB 1.0000 1 1.0000 0.94 0.3542

BB 69.0313 1 69.0313 65.14 0.0000

Total error 10.5967 10 1.05967

Total (corr.) 123.438 15

R-squared = 91.4154 percent

R-squared (adjusted for d.f.) = 87.123 percent

Standard Error of Est. = 1.0294

Mean absolute error = 0.,459596

Durbin-Watson statistic = 2.67484 (P=0.0868)

Lag 1 residual autocorrelation = -0.337422

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The ANOVA table partitions the variability in St into separate pieces for each of the effects. It then tests

the statistical significance of each effect by comparing the mean square against an estimate of the

experimental error. In this case, 4 effects have P-values less than 0.05, indicating that they are

significantly different from zero at the 95.0% confidence level.

The R-Squared statistic indicates that the model as fitted explains 91,4154% of the variability in St. The

adjusted R-squared statistic, which is more suitable for comparing models with different numbers of

independent variables, is 87,123%. The standard error of the estimate shows the standard deviation of the

residuals to be 1,0294. The mean absolute error (MAE) of 0,4596 is the average value of the residuals.

The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant correlation

based on the order in which they occur in your data file. Since the P-value is greater than 0.05, there is no

indication of serial autocorrelation in the residuals. Excluding cross-product AB

Figure 49: Pareto Chart for shrinking temperature. Experimental design III.

ST = 63.00 + 1.13 NaCOOH + 1.10 HCOOH + 1.69 (NaCOOH)2 + 2.94 (HCOOH)

2

Figure 50: Estimated response surface for ST. Experimental design III

Standardized Pareto Chart for St

Standardized effect

+-

0 2 4 6 8 10

B:HCOOH

A:NaCOH

AA

BB

NaCOHHCOOH

St

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

62

64

66

68

70

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Optimize Response

Goal: maximize shrinking temperature

Optimum value = 75ºC

Optimum value for factor NaCOOH= 1.414

Optimum value for factor HCOOH= 1.414

Results for tensile strength (Tens)

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:NaCOH 7184.83 1 7184.83 2.47 0.1473

B:HCOOH 25.06 1 25.06 0.01 0.9279

AA 22684.30 1 22684.30 7.79 0.0191

AB 2916.00 1 2916.00 1.00 0.3405

BB 7564.40 1 7564.40 2.60 0.1381

Total error 29113.30 10 29113.30

Total (corr.) 69488.00 15

R-squared = 58.1031 percent

R-squared (adjusted for d.f.) = 37.1547 percent

Standard Error of Est. = 53.9567

Mean absolute error = 28.0002

Durbin-Watson statistic = 2.36478 (P=0.2714)

Lag 1 residual autocorrelation = -0.18239

The ANOVA table partitions the variability in Tensile into separate pieces for each of the effects. It then

tests the statistical significance of each effect by comparing the mean square against an estimate of the

experimental error. In this case, 1 effects have P-values less than 0.05, indicating that they are

significantly different from zero at the 95,0% confidence level.

The R-Squared statistic indicates that the model as fitted explains 58.1031% of the variability in Tensile.

The adjusted R-squared statistic, which is more suitable for comparing models with different numbers of

independent variables, is 37.1547%. The standard error of the estimate shows the standard deviation of

the residuals to be 53.9567. The mean absolute error (MAE) of 28.0002 is the average value of the

residuals. The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant

correlation based on the order in which they occur in your data file. Since the P-value is greater than

0.05, there is no indication of serial autocorrelation in the residuals.

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Figure 51: Standardized Pareto Chart for Tensile. Experimental design III.

When excluding all effects at p-value lower than 0.05, estimated response surface is calculated as in

figure 52.

Tensile = 585.62 – 53.25 (NaCOOH)2

Figure 52: Tensile strength estimated response surface. Experimental design III.

Optimize Response

Goal: maximize Tensile

Optimum value = 585.62 N

Optimum value for factor NaCOOH= 0.0

Optimum value for factor HCOOH= 0.0

Standardized Pareto Chart for Tensile

0 0,5 1 1,5 2 2,5 3

Standardized effect

B:HCOOH

AB

A:NaCOH

BB

AA +-

NaCOHHCOOH

Tensile

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

530

540

550

560

570

580

590

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Results for elongation (Elon)

Analysis of Variance for Elongation

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:NaCOH 98.9975 1 98.9975 31.79 0.0002

B:HCOOH 2.3579 1 2.3579 0.76 0.4046

AA 36.1251 1 36.1251 11.60 0.0067

AB 25.0000 1 25.0000 8.03 0.0178

BB 6.1250 1 6.1250 1.97 0.1911

Total error 31.1446 10 3.1144

Total (corr.) 199.7500 15

R-squared = 84.4082 percent

R-squared (adjusted for d.f.) = 76.6123 percent

Standard Error of Est. = 1.76478

Mean absolute error = 0.866497

Durbin-Watson statistic = 1.68533 (P=0.3117)

Lag 1 residual autocorrelation = 0.157334

The ANOVA table partitions the variability in Elongation into separate pieces for each of the effects. It

then tests the statistical significance of each effect by comparing the mean square against an estimate of

the experimental error. In this case, 3 effects have P-values less than 0.05, indicating that they are

significant the 95.0% confidence level. These effects are % NaCOOH and its quadratic effect and the

interaction with % HCOOH.

The R-Squared statistic indicates that the model as fitted explains 84.4082% of the variability in

Elongation. The adjusted R-squared statistic, which is more suitable for comparing models with different

numbers of independent variables, is 76.6123%. The standard error of the estimate shows the standard

deviation of the residuals to be 1.7648. The mean absolute error (MAE) of 0.8665 is the average value of

the residuals. The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant

correlation based on the order in which they occur in your data file. Since the P-value is greater than

0.05, there is no indication of serial autocorrelation in the residuals.

Excluding B and BB effects with P-value less that 0.05, we obtain the Pareto chart in figure 53:

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Figure 53: Standardized Pareto chart for Elongation. Experimental design III

Elon = 42.56 + 3.52 NaCOOH + 2.13 (NaCOOH)2 – 2.5 NaCOOH*HCOOH

Figure 54: Elongation response surface. Experimental design III

Optimize Response

Goal: maximize Elongation

Optimum value = 56.79 mm

Optimum value for factor NaCOOH= 1.414

Optimum value for factor HCOOH= -1.414

Standardized Pareto Chart for Elongation

Standardized effect

+-

0 1 2 3 4 5 6

AB

AA

A:NaCOH

NaCOHHCOOH

Elo

ngation

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

38

41

44

47

50

53

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Results for tear load (tear)

Analysis of Variance for Tear

Source Sum of Squares Df Mean Square F-Ratio P-Value

A:NaCOH 58.0845 1 58.0845 1.25 0.2888

B:HCOOH 22.6323 1 22.6323 0.49 0.5003

AA 5278.7800 1 5278.7800 114.04 0.0000

AB 400.0000 1 400.0000 8.64 0.0148

BB 1140.0300 1 1140.0300 24.63 0.0006

Total error 462.8990 10 46.2899

Total (corr.) 7362.440 15

R-squared = 93.7127 percent

R-squared (adjusted for d.f.) = 90.569 percent

Standard Error of Est. = 6.80367

Mean absolute error = 3.03097

Durbin-Watson statistic = 2.12887 (P=0.4763)

Lag 1 residual autocorrelation = -0.0644357

The ANOVA table partitions the variability in Tear into separate pieces for each of the effects. It then

tests the statistical significance of each effect by comparing the mean square against an estimate of the

experimental error. In this case, the quadratic effects of % NaCOOH and % HCOOH and the interaction

effect among them have P-values less than 0.05, indicating that they are significant at the 95,0%

confidence level.

The R-Squared statistic indicates that the model as fitted explains 93.7127% of the variability in Tear.

The adjusted R-squared statistic, which is more suitable for comparing models with different numbers of

independent variables, is 90.569%. The standard error of the estimate shows the standard deviation of the

residuals to be 6.80367. The mean absolute error (MAE) of 3.03097 is the average value of the residuals.

The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant correlation

based on the order in which they occur in your data file. Since the P-value is greater than 0.05, there is no

indication of serial autocorrelation in the residuals.

Excluding A and B effects with P-value less that 0.05, we obtain the Pareto chart in figure 55:

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Figure 55: Standardized Pareto chart for tear load. Experimental design III

Tear = 89.00 + 26.69*(NaCOOH)2 – 10.0*NaCOOH*HCOOH + 11.94*(HCOOH)

2

Figure 56: Tear load estimated response surface. Experimental design III

Optimize Response

Goal: maximize Tear

Optimum value = 184.25 N/mm

Optimum value for factor NaCOOH= -1,414

Optimum value for factor HCOOH= 1,414

Standardized Pareto Chart for Tear

Standardized effect

+-

0 2 4 6 8 10 12

AB

BB

AA

NaCOHHCOOH

Tear

-1 -0,6 -0,2 0,2 0,6 1-1

-0,6-0,2

0,20,6

1

88

98

108

118

128

138

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10.4 Conclusions of the Experimental Design III:

Shrinking temperature increases with the amount of sodium formate and formic acid that means

at the highest pH conditions before the pretanning process and the lowest pH to fix the tannins at

the end, previous to the mechanical operations.

The amount of formic acid and sodium formate has not statistically significance on tensile

strength, but the effect of the quadratic % NaCOOH. Optimal values for the application are in

central points.

The amount of sodium formate, it quadratic effect and interaction with % HCOOH have

statistically significance. The increase of sodium formate increases elongation.

The quadratic effects of percentage of formic acid and sodium formate have statistical

significance on the results of tear load among the interaction. Values are optimized when amount

of sodium formate is lowered and formic acid is increased.

The amount of sodium formate or the highest pH for conditioning the pelts before the pre-tanning

process has a positive effect on the results of shrinking temperature and tensile elongation at 95%

of statistic confidence level.

The amount of formic acid or the lowest pH at the end of the pre-tanning process in order to fix

non-exhausted tannins on the collagenic structure, has a positive effect on the results of shrinking

temperature at 95% of statistic confidence level.

The calculated optimal values obtained from the mathematic models for each of the variables considered

in this Experimental Design III are summarized on table 45:

NaCOOH HCOOH

Shrinking Temperature 1.414 1.414

Tensile Strength 0.0 0.0

Elongation 1.414 -1.414

Tear load -1.414 1.414

Table 45: Optimal values for each variable. Experimental Design III

These values will be considered according to the requirements of the final article to be manufactured with

the subsequent processes of retanning, fatliquoring, dyeing and finishing.

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Shrinking temperature needs to be maximized for ensure heat resistance to the mechanical treatments

after Pretanning, mainly in shaving to obtain appropriate and regular thickness among the different parts

of the hides or skins.

The physical properties will depend on the performance of the goods manufactured with the leather

article. While tear load is an important property for apparel, elongation is fundamental for the

manufacture of shoes where leather is exposed to high tensile forces.

In general, however, all these physical properties considered in this thesis are common for most of the

leather articles produce for the shoe, apparel, upholstery and leather good markets, thus the mean of all

these coordinate values is considered as the most balanced value:

Coordinate value NaCOOH = Me [ST, Tens, Elon, Tear] = 0.707

Coordinate value HCOOH= Me [ST, Tens, Elon, Tear] = 0.707

According to the formulas for Codification Table, Design III, Table 40, for sodium formate:

Vx = (V0-V-1.414)(x+1.414)/1.414+V-1.414

V0.707 = (0.5-0)(0.707+1.414)/1.414 + 0 = 0.75

% NaCOOH = 0.75 %

According to the equation of the fitted model to describe the relationship between pH and independent

variable of % NaCOOH through a multiple linear regression model as defined in 10.2.1, the optimal

conditioning pH of pelts previous to the pre-tanning process with tara tannins is:

pH = 3.15 + 2.78*NaCOOH = 5.23

According to the formulas for Codification Table, Design III, Table 40, for sodium formate:

Vx = (V0-V-1.414)(x+1.414)/1.414+V-1.414

V0.707= (0.6-0.2)(0.707+1.414)/1.414 + 0.2 = 0,80%

According to the regression equation of the fitted model to describe the relationship between pH and

independent variable of % NaCOOH and % HCOOH as defined in 10.2.2, the optimal conditioning pH of

pelts previous to the pre-tanning process with tara tannins is:

pH final = 3.65 + 0.31*% NaCOOH – 0.16*% HCOOH – 0.19 * (%NaCOOH)2 =

pH final = 3.65 + 0.23 – 0.13 – 0.11 = 3.64

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These results applied to the recipe for wet-white with tara tannins are shown in table 46.

Table 46: Final recipe for wet-white with tara tannins

Operation % Product T oC Running time Control

Conditioning 50 Water 20

4 Sodium chloride

10 min.oBè=6

Add hides to drum 10 min. pH= 3.3

Depickling 0.75 Sodium formate

0.38 Sodium bicarbonate 120 min. pH= 5.23

Drain

Pretanning 50 Water 20

12 Tara powder

7 Naphthalene sulphonic syntan liquid Overnight

0.8 Formic acid 85% 120 min. pH=3.64

Drain

Washing 300 Water 20 20 min.

Drain

Horse up. Samming. Shaving.

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11. Thesis practical validation: Manufacturing a sustainable

automobile-interior leather article.

Beyond the mathematic models used to validate this thesis, the latest section of the research intends to

present the manufacture an automobile-interior leather article base on the results from previous sections.

Therefore, a full bovine hide was processed with a wet-white formulation based on tara tannins at pilot

scale. The hide was split in two sides for better handling. After pretanning according to the findings

developed during the experimental designs, sides were shaved to the thickness for the required car

upholstery, retanned, fatliquored and dyed following a standard formulation. One of the sides was

finished to manufacture a headrest of a car seat, while samples were prepare according to International

Standard EN ISO 2419 / IUP 1 and IUP 3, “Leather – Physical and mechanical tests – Sample preparation

and conditioning”51,

52

.

Material: Pickled pelt from Russia bovine hide. pH = 3.5. Total weight 11.580 kg. Side 1: 5.260 kg. ; side

2: 6.320 kg.)

Equipment: Simplex DF drum.

Procedure: Drums are empty. Pelts horsed up.

Operation ºC % Product Time Remarks

Conditioning 20 200 Water

12 Common salt 10 min oBè = 5.5.

Add pelts to the drum Over night

Drain

Depickling 20 50 Water

4 Common salt 10 min oBè = 7

pH = 3

0.75 Sodium formate

0.38 Sodium bicarbonate 2 h. pH = 3.78

Note 1

1.2 Sodium formate

0.6 Sodium bicarbonate Over night pH = 5.20

Drain

Pretanning 20 50 Water Note 2

12 Tara powder Note 3

7 Naphthalene sulphonic syntan (1:10) 6 h

0.5 Formic acid 85% (1:10) 30 min. pH = 3.82. Note 4

0.6 Formic acid 85% (1:10) 2 h pH = 3.6

Drain

Washing 20 200 Water 15 min.

Drain

51 Normas IUP. Ensayos físicos de curtidos. Asociación Química Española de la Industria del Cuero. Octubre 2001. Pag, 3 and 12.

52 Journal of the Society of Leather Technologists and Chemists (JSLTC). Volume 82. September-October 1998. Number 5. ISSN 0144-0322. Pages 190. 192 and 199.

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Washing 20 200 Water 15 min

Drain.

Horse up (Note 5). Samming. Shaving to 1.2 mm thickness (Note 6)

Note 1: Due to the high acidity from preserving pickle, % of sodium formate and % of sodium

bicarbonate have to be increased to achieve the desired pH of 5.23. To ensure pH is completely through

the pelt section, drum is running over night.

Note 2: At the pH of 5.2, collagen does not swell thus addition of common salt is not necessary53,54

.

Volume of bath has to be minimized to increase mechanical action and aid the penetration of the

chemicals in the inner layer of the collagen structure.

Note 3: Tara powder is added in solid form to avoid a quick reaction on the pelt surface, thus blocking

tannins to be diffused inside the structure.

Note 4: The tanning completion was visually checked. A thin layer remained white but, checking with

ferric sulphate (dark blue indicator), it showed a complete vegetable tanning through the cross section of

the leather. % of formic acid needed to be adjusted to achieve the pH of 3.64.

Note 5: Leather was very clean with uniform light brown color. Shrinking temperature achieved 70º C

considering that the tanning was completed. Bath contained a high amount of insoluble matter.

Superficial astringency on leather surface was characteristic of leather tanned with vegetable tannins.

Note 6: After shaving leather was completely stained with dark blue spots. After cleaning with a chelating

agent, e.g. ethylenediaminetetraacetic acid (EDTA), stains were removed and the even light brown color

was fully recovered. Leather resisted and damage of shrinking was not observed. The behavior for

shaving operation was optimal due to the superficial astringency.

The two shaved sides were weighted. Total shaved weight 5.650 kg (50% of pelt weight). Sides were

loaded to the Simplex DF drum.

Operation ºC % Product Time Remarks

Washing 35 300 Water

0.5 Oxalic acid

0.5 EDTA

0.3 Non-ionic degreasing agent (45%) 30 min.

Drain

Washing 35 300 Water 15 min

Drain

Retanning 30 150 Water

53 E. Gratacos, J. Boleda, M. Portavella, J.M. Adzet, G. Lluch. Tecnología química del cuero. Barcelona 1962. Pag. 47

54 Antoni Ylla-Catala. La Ribera. Grup Colomer. Vic. 2008. Pag. 34.

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3 Neutral salt of dicarboxilic acid with

buffering effect. Powder

1 Sodium formate

0.3 Sodium bicarbonate 30 min pH = 4.7

Fatliquoring I 1 Anionic phosphoric ester 55%

3 Animal sulphitated oil 80%

3 Mixture of synthetic oils 40 min

1.5 Neutral salt naphtha. sulphonic acid

6 Synthetic substitution syntan 96%

0.5 EDTA

10 Tara powder 60 min

Dyeing 0.5 Neutral salt naphtha. sulphonic acid

3 Metal-complex grey dye 60 min

Overnight 15 min/hour

50 80 Water

1.5 Formic acid 85% (2x15 min) 60 min

Drain

Washing 50 300 Water 15 min

Drain

Fatliquoring II 50 200 Water

7 Animal sulphitated oil 80%

4 Anionic phosphoric ester 55% 60 min

4 Protein based syntan 15 min

2 Tara powder 20 min

1 Formic acid 85% (2x10 min) 30 min pH = 3.4

Drain

Washing 20 300 Water 20 min

Drain

Horse up 24 hours. Samming. Vacuum dry. Hang for drying. Toggling. Staking. Conditioning.

Thickness: 1.5 mm

Samples were prepared and conditioned from one of the sides according to “EN ISO 2419 IUP 1 & IUP3,

Leather – Physical and mechanical tests methods – Sample preparation and conditioning” for quality

testing. The rest of the side was finished by coating polyurethane resins, cross-linkers and auxiliaries to

obtain the final feel and esthetics required for a commercial article. The side was milled, shaved to 1.2

mm of thickness and printed. See photo 15.

The European standard “prEN 14906 – Leather – Leather for automotive – Tests methods and testing

parameters” gives guidelines to select the test methods to assess the performance of leather for

automotive. The parameters for testing are divided in fundamental and complementary properties.

Fundamental properties consider basic parameters (apparent density mass per unit area and thickness),

tensile properties, stiffness in blending, durability/wear, ageing, lightfastness, fastness, emission behavior

and others. Most of these parameters refer to the finishing properties or substances beyond the scope of

this thesis. For this reason, quality tests focus on tensile and ageing properties that can be influenced by

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the pretanning operations. Furthermore, lightfastness is also assessed as an added value of tara tannins to

the final article despite the latest rating is obtained when coating with pigments. In any case, it is well

known that higher lightfastness in crust can avoid excessive use of pigments, thus, natural aspect of the

final article can be preserved if the quality of the grain is acceptable.

Photo 15: Car-interior leather from pretanning with tara tannins.

Top: crust after wet-end. Down: finished article

Test methods and results, according to prEN 14906 guidelines are indicated in table

Test method Concept Expression of results Result

EN ISO 3376 / IUP 6 Tensile strength NPa 10.2±0.1

EN ISO 3376 / IUP 6 Percentage elongation at break % 41.1±1

EN ISO 3377 / IUP 8 Tear load at single edge N 54.6±0.1

ISO 105-B02/IUF 402 Lightfastness (photo 16) Blue scale 3

EN ISO 17227/IUP 35 Dimensional stability % 150ºC/15 min

% 150ºC/30 min

% 150ºC/60 min

% 200ºC/15 min

2.8±0.2

2.8±0.2

3.4±2

burning

Table 47: Quality test results. Car-interior leather from pretanning with tara tannins.

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Photo 16: Blue scale for lightfastness

Those quality results can be compared with the technical specifications that car manufactures request to

their suppliers to be completely fulfilled according design car models. For this reason three European

Original Equipment Manufacturers (OEM) of automobile groups were approached to obtain information

on engineering material data that have to be conformed to the Companies in leather deliveries to the

vehicle manufacturing chain. Those groups were Volkswagen, Ford and PSA Peugeot – Citroën.

Due to industrial confidentially, the whole documents cannot be reproduced in this research report.

Despite each OEM have its own standards for testing, Volkswagen and Ford follow the ISO standards or

values that can be compared, while PSA cannot be considered in this assessment.

Tensile strength:

Volkswagen: ≥ 130 N

Ford: ≥ 125 N

Manufactured leather article pre-tanned with tara = 10.2 Npa

The tensile strength, Tn, in NPa is calculated using the equation:

Tn = F / w * t → F = Tn * w * t

F = highest force recorded in N

w = is the mean width of the test piece, in mm. 10 mm has been applied

t = is the mean thickness of the test piece, in mm. 1.5 mm as indicated

Tn = 10.2 NPa * 10 mm * 1.5 mm = 153 → Pass

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Tensile elongation at break:

Volkswagen: 35 – 60 %

Ford: 30 – 70 %

Manufactured leather article pre-tanned with tara = 41.1 % → Pass

Tear load:

Volkswagen: ≥ 25 N

Ford: 70 N (ASTM D 5733 not comparable with ISO 3377)

Manufactured leather article pre-tanned with tara = 54.6 N → Pass (for VW)

Lightfastness:

Volkswagen: ≥ 3 rating

Ford: 225.6 kJ/m2, rating 3; 488.8 kJ/m

2, rating 4

Manufactured leather article pre-tanned with tara = 3 → Pass

Considering that manufactured leather article pre-tanned with tara is not finished and selected pigments of

normal application in tanneries increase this property.

Dimensional stability:

Volkswagen: ≤ 5 % (120ºC/168 h)

Ford: ≤ 5 % (100ºC/3 cycles)

Manufactured leather article pre-tanned with tara = 3.4 (150ºC/60 min).

Test methods differ, but shrinking, in any case, is lower that requirement → Pass

These results confirms that pre-tanning (wet-white) with tara tannins and according the proposed

technology described in this thesis, the quality requirements for leather articles for vehicle interiors can

be achieved. It is important, however, to point out that the final properties will also depend on other

substances and operations during the whole processing, e.g. fatliquors, retanning agents and finishing.

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12. Final conclusions

This thesis has validated the compliance of the two major hypotheses of sustainability and innovation

implicit in the title of the work. It proves the fact that tannins from the pods of tara fruits are able to

respond as newest technologies of tanning leather complying article quality standards and meeting the

highest exigencies of sustainability required by consumers and general community.

The tara sourcing of tannins has been assessed by approaching the values to the “Triple Boton Line”

objectives of environment (planet), social (people) and economic (profit) while experiments have been

designed in order to optimize a wet-white recipe to be submitted to the chemical and mechanical

treatments in order to manufacture all kind of articles and able to meet the physical requirements for

consumer leather goods.

Environment: The agro forestry of the tara tree benefits to the environment with important

contributions to the fixation of carbon and nitrogen to the soil, as alternative to reforestation and

protection to soil erosion. It enables ecosystems to survive and minimize consumption of materials

which exploitation requires energy and water among other resources or, contrary to other vegetable

tannins, production does not depend from other industries or implies deforestation. Tara tannins are

renewable as they are available in a continually renewing matter. Regulations of chemicals, mainly in

Europe, recognize the use of non-hazard substances from natural origin if not chemically treated.

Social: The tara tree is suitable for agro forestry and represents a source of economical activities for

Andean Regions by exporting products to the leather markets. Also, other products from the fruit of

tara are very valuable in other industries as gum for food and industrial applications and polyphenols

with properties in medicine. Its application in tanneries and leather articles is safe for workers and

consumers.

Economic: The fruits of the tara tree contain valuable substances. Among them, the pods are high

concentrated in tannins. Agro forestry is the solution to ensure quality and consistency on production

volume and prices to supply the high potential demand of tannins for the world wide leather

production. Leather treated with tara tannins are white and had excellent light fastness and, therefore,

are specially suitable for pastel shades in articles submitted to extreme atmospheric conditions. The

automobile industry is concerned on green issues and strictly claims to suppliers recyclable materials

or, if disposal, the lowest environmental impact. The wet-white leather solves these requirements.

Tanners manufacturing this kind of leather articles use tara as a retanning agent while glutaraldehide

is the main tanning agent.

The hypothesis of tara pre-tanning process as innovative technology in the leather making is proven with

the analysis of the performance of the pelts submitted to the treatment of tara, blended with general

synthetic tannin groups, at different ratios and application conditions.

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Tara commercial samples from various suppliers were analytically characterized by means of pH, and

content of water, total solids, soluble solids, non-tannins, tannins and insoluble matter, and compared to

determine significant differences among them. All these variable results from the chemical tests did not

showed significant statistic differences and deviations among them did not exceed the limits of a normal

distribution.

Commercial tara powders currently available in the market are reach in tannins (ca. 50%) and content a

high amount of insoluble matter (>20%).

The normal distribution was used for comparing further characterizations of tara powder processed in the

laboratory from fruits obtained in different regions of Bolivia. Despite their natural origin of tara powder,

composition of ingredients maintained consistent ratios. Therefore, agro-forestry of tara is suitable in a

wide range of climate conditions without significant deviation in their composition.

A correlation of non-tannins content and the Gallic acid hydrolyzed from tannin molecule was tested but

not proven as the null hypothesis could not be statistically rejected. However, the hydrolysis of Gallic

acid can be explained after the treatment of tara powder exposed to time and temperature according to the

lineal function:

Content of free Gallic Acid (mg/kg) = 1,224.1 + 15.9 T

The hypothesis of tara pre-tanning process as innovative technology in the leather making has been

proven with the analysis of the performance of the pelts submitted to the treatment of tara, blended with

general synthetic tannin groups, at different ratios and application conditions.

The tara tannins are suitable to transform collagen protein into leather by stabilizing its structure from

hydrolysis, mainly bonding the CO-NH linkage of the protein through the phenolic hydroxyl group,

among other side reactions.

Experimental Design I, blend of tara powder with syntans, naphthalene sulphonic or auxiliary type and

phenol condensation or substitution type have shown that the tara powder has good properties because its

tanning effect, but it has certain limits to react in the interior of the deeper layers of the collagen structure.

Results have demonstrated that the blend with naphthalene sulphonic syntan is the most suitable for

tanning with tara tannins acting as a dispersant auxiliary.

Design II has optimized the ratio of components of the blend of tara tannins with a naphthalene sulphonic

syntan.

Synergy is obtained by increasing the values of naphthalene sulphonic when tara has limits:

shrinking temperature due the improvement of the tara tannin penetration, tensile elongation an

tear load.

Considering the optimal combinations for each variable, the mean of the variables and the

concentration of tannins, the calculated ration among them is:

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67 parts of tara tannin

33 parts of naphthalene sulphonic syntan

Design III has optimized the conditions for best application of the bend obtained in the Design II, by

means of measure of pH at the beginning and at the end of the process using a blend of sodium formate

and sodium bicarbonate (2/1) and formic acid, as pH regulator agents. The calculated optimal pH has

been:

pHinitial = 5,23

pHfinal = 3,64

The results of the experimental research have been validated with the complete manufacture of a leather

article for automotive interior and physical tests reject the null hypothesis (tara tannins are not suitable for

wet-white).

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13. Recommendations for new researches.

The conclusions of this thesis can support further experiments to develop technologies for a new range of

leather articles. Their objectives need to focus on satisfying increasing demands of sustainable and safe

material used for manufacturing goods like shoe, apparel or upholstery.

Design of new formulations using sustainable vegetable tannins to manufacture eco-friendly leather

articles by improving the competitiveness of SMEs in the International leather market have to be

evaluated as a substitution of the chrome tanning for high quality leather. Limits of the cross-linking

between the tara tannins and the collagen structure have been solved in this research by blending them

with synthetic tanning agents, naphthalene sulphonic syntan, mainly. This was due to the current situation

of the supply chain of the tara fruit by-products and the simplicity of the process also constrained by

costing factors. However, new researches are necessary to obtain and concentrate the tannins with better

properties according the final leather articles quality requirements. Therefore, new works can focus on:

Removal or reduction of insoluble matter from tara powder, either by sieving or filtering a

solution. In any case, the filling effect of insoluble matter during the tanning operation has to be

considered for certain articles. Solubilization technologies of this matter with certain chemical,

e.g. sulphitation commonly used for other vegetable extracts as sweet quebracho, has to be

observed if further commercialization is possible or registrations are required due to the

subsequent chemical molecule modification.

Extraction of tannins to increase the active matter for commercial products. As tara tannins are

hydrolysable, water solution at certain temperature and concentration by evaporation or

atomization can be processed without the need of registration in REACH. Hydrolysis conditions

need to be considered to avoid an excess of non-tanning matter (e.g. Gallic acid and polymers of

low molecular size).

Research of properties of tannins according to their molecular size. Fractions of tannins can be

separated by, e.g., reverse osmosis, and tanning properties can be assessed from light to heavy

portions to be applied according the needs of specific articles.

Other blends, besides the syntans analyzed in this thesis, can be assessed considering other

environmental needs. E.g., mixtures with other vegetable tannins either hydrolysable like chestnut

or polyflavonoids tannins like quebracho or mimosa.

The first part of this thesis focuses on the concept of sustainability in general terms with the aim to

validate the hypothesis within the scope of this research. However, new researches are necessary to assess

all the aspects of the concept according to the sections 1 and 2.

Life cycle assessment to the three bottom lines: social, environmental and economic. The holistic

approach have to include not only the raw material production that has also other considerations

mentioned underneath, but manufacture, logistics, uses and disposal of the consumer articles.

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A very special emphasis requires the strategies to mitigate the climate change and the reduction

of greenhouse gases. Forestry plays a critical role in the carbon cycle by absorbing carbonic

dioxide from the atmosphere through the photosynthesis mechanism and accumulating carbon as

biomass. Currently, carbon market regulations are under big discussion in international forums or

become voluntary as a sustainable responsibility of corporations and societies. The contribution

of the tara agro-forestry could be assessed under the United Nations Framework Convention on

Climate Change (UNFCCC) and/or the Kyoto Protocol (PK) to fight global warming. Therefore,

despite the incipient and complexity of forestry projects, it is necessary to include tara agro-

forestry to pull towards international investments and support the use of natural substances for

traditional and well established industries like tanning, as alternatives to expensive synthetic

materials.

Assessment of leather article consumer good disposal after their use-life. Differently from other

tanning substances, mainly chromium, tanning with tara leather maintains as organic material.

Disposal of leather and by-products like shavings and trimmings can find further uses like

fertilizers or, at least, high disposal costs.

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14. Bibliography

Agroforestry Database 4.0. World Agroforestry Center. Nairobe. (Date of consultancy October, 24, 2009)

http://www.worldagroforestry.org/treedb2/AFTPDFS/Caesalpinia_spinosa.pdf

Almeida e. Taller Regional de la Tara. ECOBONA. Cajamarca 24-27 october 2007

Asociación Química Española de la Industria del Cuero. AQEIC Normas IUP. Ensayos Físicos de

Curtidos. Octubre 2001

Bacardit A., L. Ollé. Diseño de experimentos en ingeniería del cuero. Escola d’Enginyeria d’Igualada.

Escola Superior d’Adoberia d’Igualada. ISBN: 84-931837-8-4

BASFOR: Semillas Forestales – Plantas y Asesoramiento técnico. Centro de Semillas Forestales. ESFOR

(School of forest science. Universidad San Simón. IC / Cosude. Avda. Atahualopa, final norte s/n.

Cochabamba. Bolivia. (Date of consultancy June, 12, 2009)

http://www.umss.edu.bo/Academia/Centros/Basfor/

Bienkiewicz Krysztof. Physical Chemistry of Leather Making. Rober E. Krieger Publishing Company.

Malabar, Florida, USA. 1983.

Convington, A. G. Lampard, R. Hanco*ck, I. Ioannidis. Studies on the origien of hydrothermal stability. A

theory of tanning. Journal of the American Leather Chemists Association, 93 (1998)

Convington, A. L. Song, O. Suparno, H. Koon, M.J. Collins. Link-Lock: An explanation of the chemical

stabilization of collagen. World Leather. October/November 2010

European Commission. Integrated Pollution Prevention and Control (IPPC). Reference document on Best

Available Techniques for the Tanning of Hides and Skins. 2003

European Union, Oficial Journal of the. Regulation (EC) No 1907/2006 of the European Paliament and of

the Council of 18 December 2006. L 396/1. 30.12.2006

Font, J. Análisis y ensayos en la industria del cuero. Escola Universitaria d’Enginyeria Tècnica

d’Igualada. 2002. ISBN: 84-931837-5-X.

Garro, J.M, Galvez, B. Riedls and A.H. Conner. Analytical studies on tara tannins. Departement des

Sciences du bois et de la Forêt, Centre de Recherche en Sciences et Ingénierie des Macromolécules,

Université de Laval, Quebec. Canada. USDA-Forest Service, Forest Products Latoratories, Madison

USA. Holzforschung. Vol 51.1997. Pag. 235-243. Walter de Gruyter. Berlin. Germany.

Glavic, Peter, Lukman Rebeka, University of Maribor, Demartment of Chemistry and Chemical

Engineering, Slovenia. Review of Sustainability terms and their definitions. Journal of Cleaner

production. 15 (2007). 1875-1885.

Gratacos E., Boleda J., Portavella M., Adzet J.M., Lluch G. Tecnología química del cuero. Barcelona

1962.

Haslam, E.. Chemistry of vegetable tannins. Department of Chemistry. The University, Sheffield,

England, Academic Press, London. 1966.

ICT, Leather Trade House, , Kings Park Road, Moulton Park, Northampton, NN3 6JD, UK, (Date of

consultancy May, 15, 2010) www.tannerscouncilict.org

Mancero L., 2008, La Tara (Caesalpinia spinosa) en Perú, Bolivia y Ecuador: Análisis de la Cadena

Productiva en la Región. Programa Regional ECOBONA – INTERCOOPERACIÓN, Quito. Quito,

febrero 2009

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Marrwijk, Marcel van, Concepts and Definitions of CSR and Corporate Sustainability: Between Agency

and Communion. Journal of Business Ethics, 44, 95-105, 2003. Netherlands.

Marrwijk, Marcel van and Were, Marco, Multiple Levels of Corporate Sustainability.

http://www.vanmarrewijk.nl/pdf/021206131353.pdf. September 2002

Morera, Josep Mª. Química Técnica de la Curtición. Escola Universitaria d’Enginyeria Tècnica Industrial

d’Igualada. Escola Superior d’Adoberia. ISBN 84-931837-0-9.

Programa Nacional ECOBONA. Portal de Bosques Andinos (Date of consultancy December, 1, 2009)

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Programa Regional ECOBONA-INTERCOOPERACION. “La Tara (Caesalpinia spinosa) en Perú,

Bolivia y Ecuador: Análisis de la Cadena Productiva en la Región”. Serie Investigación y

sistematización. Vol. 02. Quito. 2009.

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Service Center. Media and Communications. Ludwigshafen. Germany. 2007.

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10: 0787979074 | ISBN-13: 978-0787979072

Schiaffino, JC. Estudio del mercado de la Tara. Perú Programa Desarrollo Rural Sostenible, GTZ,

Universidad del Pacífico, GOPA. 2004.

M. Skowyra M., Dávila M, Fabregat C., Castell J.C, Almajano M. P. Actividad Antioxidante de la vaina

de tara. VI Congreso Nacional de Ciencia y Tecnología de los Alimentos. Valencia, 8-10 June, 2011.

SILVATEAM. Silvachimica S.r.l. Via Torre 7. San Michele di Mondovì (CN). Italia. TE:

+39.0174.220256. (Date of consultancy September, 15, 2009) http://www.silvateam.com/

Stavins, Robert N., Post-Kioto International Climate Policy. Summary for policy markets. Research for

the Harvard Project on International Climate Agreement. Cambridge. MA. USA. 2009.

ISBN:9780521138000

Tara Casealpina spinosa. Market Survey. Compiled by Swiss Import Promotion Programme (SIPPO) by

ProFound – Advisers In Development 2008/2009.

Thorstensen Thomas C.. Practical Leather Technology. Robert E. Krieger Publishing Company.

Malabar, Florida. USA. 1985

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Profile. Caesalpinia Spinosa (Molina) Kuntze. (Date of consultancy December, 13, 2009).

http://www.plants.usda.gov/java/nameSearch

U.N. Documents. Report of the World Commission on Environment and Development: Our Common

Future. Chapter II: Towards Sustainable Development. UN Documents: Gathering a Body of Global

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NGOs from United Nations web sites

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Wilson, John Arthur. The Chemistry of Leather Manufacture. The Chemical Catalog Company Inc. New

York. U.S.A. 1928.

Ylla-Catala A. La Ribera. Grup Colomer. Vic. 2008.

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15. Acknowledgements

I express my appreciation to the directors of the thesis, Dr. Anna Bacardit and Lluís Ollé, Escola de

Enginyeria d’Igualada – Universitat Politècnica de Catalunya (EEI-UPC) for his helpful guidance. To Dr.

J.M Adzet, Dr. Joaquim Font (EEI – UPC), the project department, experimental plant and testing

laboratory of the Association for Research of the Leather Industry and Annexes (AIICA), Igualada; Mr.

David Solano, Director of the International Department and the Technical Department, Centre Tecnològic

Forestal de Catalunua (CTFC), Solsona; Dr. Fimo Aleman, research director of BASFOR – Universidad

San Simón, Cochabamba, Bolivia; Mr. Josep L. Torres, managing director and the technical department

of Leather Química – Mathiesen Group, Dr. Luminita Albu. director of the Research-Development

National Institute for textile and Leather (INCDTP), Bucharest, Romania, Dr. Carmen Gaidau, head of

the leather department, INCDTP, Division Leather and Footwear Research Institute (ICPI).

Photos: Joan C. Castell, Dr. Fimo Aleman, AIICA, David Solano, CTFC

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Tara (Caesalpinia spinosa):

The sustainable source of tannins for

innovative tanning processes

ANNEXES

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Annex 1: Botanic characteristics of Caesalpinia spinosa

Etymology:

Caesalpinia in honor to Andrea Caesalpini (1524 – 1603), Italian botanic and philosopher.

Spinosa: from Latin spinosus – a – um, spiny

Origin: Unknown (Cardenas, 1989).

The tree:

Photo 17: Caesalpinia spinosa (tara): the tree.

The tara tree is small, only 2 – 3 meters high, but oldest species can achieved up to 12 meters; short,

cylindrical and sometimes twisted trunk with a dark grey bark with scattered prickles, with dense and

rising branches and twigs, sometimes from the lowest part, and leafy and umbrella-shaped top. Pivot roots

and abundant secondary roots. It is a leguminous plant and fixes the nitrogen. BASFOR55

reports selected

trees to supply germoplasma of 3 – 11 m. high, trunk diameter average 22 cm, and top diameter of

average 5 m.

55 BASFOR: Semillas Forestales – Plantas y Asesoramiento técnico. Centro de Semillas Forestales. ESFOR (School of forest sc ience.

Universidad San Simón. IC / Cosude. Avda. Atahualopa, final norte s/n. Cochabamba. Bolivia. (Date of consultancy June, 12, 2009)

http://www.umss.edu.bo/Academia/Centros/Basfor/

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Leaves:

Photo 18: Caesalpinia spininosa (tara): leaves.

Alternate composed, like feathers, slightly prickly, ovoid and brilliant leaflets of dark green color

measuring 15 cm of length.

Flowers:

Photo 19: Caesalpinia spinona (tara): flowers

Hermaphrodites, yellow to red color, grouped in grapes at the extreme of the terminal branches. Flowers

are 15 to 20 cm long, irregular and tubular calyx, short twice bigger than stamens, long sepals, corolla

with free petals, grapes 8 – 15 cm. long.

Fruits and pods:

Photo 20: Caesalpinia spinosa (tara): the fruit

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The fruit of Caesalpinia spinosa is a flat yellow to orange pod up to 10 cm long and 2 cm wide. They are

fragile when are dry. Every pod contains up to 7 round seeds with a diameter of 5 to 7 mm. The color of

the seeds is dark red when mature.

They weight 3,3 g average, what means one kg of seed needs 305 fruits.

Photo 21: Tara agro forestry exploitation in Peru

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Annex 2: General chart of integrated tara fruit industrialization

GENERAL CHART OF INTEGRATED TARA FRUIT INDUSTRIALIZATION

TARA PODS

Tara threshed Seeds

Tara powder Tara extract Gallic acid Protein Gum chips

Tanning Industry Propilic / Octilic / Balanced food Tara Gum powder

Dodecil Gallate

Tannic acid Pirogallol Blended with other hydrocolloids

Trimetoxi Benzene Trimetoxi Benzaldehide Trimetoxi Acetophenon

TARA Y SU INDUSTRIALIZACIÓN INTEGRAL. Luís Germán Zúñiga Sánchez. Sociedad Mercantil Exportación (SOMEREX). October 2009

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Annex 3: Pretanning-retanning recipe for leather car upholstery

Article: Soft nappa, chrome-free for car interior.

% calculate on pelt weight

Hides are soaked, limed, unhaired, delimed, bated and pickeld as usual process in factory.

pH before pre-tanning = 3 – 3,1

Operation % Product Time Control

Pre-tanning 2,5 Glutaraldehyde 30% 2 hours pH = 3

2 Basifying 3-4 hours pH=3,9

3 Sulphonic syntan 3-4 hours

Run 10 1t 10 rpm minutes every hour overnight. Next morning: adjust pH=4–4,1

Wash and drain. Shaving to 1,2 mm. thickness to obtain WET-WHITE

Washing 200 Water 30ºC 10 min.

Drain

Retanning 200 Water 30ºC

0,3 Sodium formate

0,3 Sodium Bicarbonate 20 min pH 4,9

6 Liquid sulphonic syntan 20 min pH 4,5

2 Synthetic oil 20 min

8 Liquid sulphonic syntan

5 Granulated sulphonic syntan 20 min

5 Tara powder

8 Liquid sulphonic syntan

5 Granulated sulphonic syntan

5 Tara powder 60 min

Dyeing 1 Amphoteric dyeing auxiliary

1 Dyes

Overnight. Run every 10 min

360 min

1 Formic acid 85% 60 min pH 3,8

Drain

Washing 200 Water 50ºC 10 min

Drain

Fatliquoring 200 Water 50ºC

8 Synthetic oil

2 Lecithin oil 60 min

1,5 Formic Acid 85% 30 min

Drain

Washing 200 Water 40%

0,2 Anionic tensoactive 10 min

Drain

Unload

Horse up and mechanical operations

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Photo 22: Automobile car interior. Auto leather upholstery

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Annex 4: Tara fruit supply chain.

Forestry farmers:

Photo 23: Young tara forestry. Cochabamba. Bolivia

The forestry farmers own or rent areas where tara trees grow, either in plantations or wildly.

When pods are ripe, they fall down and farmers harvest them to be traded in local markets or to

be sold to the collectors.

Most of these farmers have 4 or 5 trees in their properties but also big farms growing up large

forests can be found.

During the execution of this thesis, it was possible to visit a farm 100 kg south Lima. The farm

includes a huge production of sugar-cane with mechanized harvest. The areas where machines

are not able to work properly, it is used for growing tara forests but profiting, also, manpower

and other equipment like watering facilities.

Production is responsibility of the farmers. The farmers prepare the soil, weed, sow, fertilize,

irrigate, trim and harvest. The farmers also sort the production.

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Collectors / wholesalers

Photo 24: Collectors and wholesales dealing with tara pods

Collectors, known in the Andean regions as a “acopiadores”, buy and gather the pods from

different farmers. They organize bulk, unload, sort, store, load and transport the products.

Collectors / wholesalers may be:

Local collectors: they buy from small farmers and sell to intermediates. Most of them

deal with more than one single intermediate of directly to the exporters. Generally, they

are financed by intermediates that advance capital to deal with farmers.

Intermediary collectors: They obtain the pods directly from farmers or local collectors

and they are the linkage with the transforming industries or the exporters.

The farmers and collectors that harvest the tara fruits sell them to the open market to the highest

bidder. Supplies of tara from these producers do not meet demand and large buyers that

purchase large amounts of tara.

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Transforming industries:

Photo 25: Tara powder mill. El Callao. Peru

Transforming industries process the pods of the harvested tara trees to obtain the products ready

to supply the different industrial sectors.

They receive the raw material from their own collectors, from intermediaries or directly from

the farmers. They control the quality and the weight of the batches of pods, before processing

and packaging. At the end, they deal with exporters.

Processing adds value to the physical product. Processing mainly takes place in Lima, where the

companies are located with the equipment which is required for processing tara. The activities

undertaken by processors are unloading, storage, processing, selection, packaging and transport.

Exporters

They are dealers. They buy tara tannin powder from manufacturers and sell to customers,

mainly in foreign countries were product is distributed.

Export is the last step in the supply chain before the product enters in the targeted market.

Exporters arrange international transport and deal with customs. They also coordinate the

wholesale and processing of the product to be able to supply their customers on time.

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Other actors:

Transport and logistics: Either some private and other public companies transport the

products from the farms to the local markets in provinces or from them to the

manufacturers or to the exporters..

Technical services

Forest Caesalpina spinosa plants

Cattle farms: manure

Nurseries: seeds

Equipment suppliers: manure, equipment

Other activities to be considered during the value chain include alternatives like organic

production, grading tara seeds according to origin, resistance to illnesses, and ration of target

products to be obtained, minimizing contamination by improving hygienic production

conditions (HACCP), grinding of the endosperm to produced a powder, further grinding with

finer mesh sizes, blending tara with auxiliaries to produce formulations which tailor to specific

needs of end-users, packaging in paper bags with polyethylene lining (plastic inner bag),

information provision (improving documentation), improving test method for analysis and

quality control, etc.

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Annex 5: Tara production in Peru, Bolivia and Equador

Production in Perú

According to Prompex56

Perú produced in 2005, 13.264 tons of tara pods. The primary

production regions were Cajamarca (36%), La Libertat (22%), Lambayeque (21%), Ayacucho

(7%) and Huánuco (5%).

ECOBONA57

estimated a production of 24.038 tons of tara fruits in 2007, 100% processed in

the country.

The transformation of tara fruit resulted in 17.033 tones of tara products, distributed as 75% in

tara powder, 11% in tara gum, 4% as a tanning agent, e.g. tara extract, 4% as a micro powder,

5% seeds and 2% others.

56 Comisión de Promoción del Perú para la Exportación y el Turismo. Ministerio de Comercio Exterior y Turismo. 2005

57 Almeida e. Taller Regional de la Tara. ECOBONA. Cajamarca 24-27 october 2007.

Region Ha Production %

Cajamarca 1328 10624 48%

La Libertad 427 3418 15%

Huánuco 311 2489 11%

Ayacucho 542 4338 20%

Other 159 1270 6%

2767 22139 100%

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In 2005, Italy was the major destination of Peruvian tara products, 17%, followed by Argentina

16% and Brazil 15%. China imported that year 6% of the total production of tara products.

However, during the last 3 years, exports to China increased from 1.000 tons in 2005 to 6.000 in

2009, half of the total exports. Argentina reduced drastically imports in the period 2008 – 2009

near 40% due to the strong reduction of leather for automobile. Argentina was the main supplier

for automotive leather since the decade of the nineteen’s but due to the international crises that

affected automotive industry, especially in the USA, production went back to classical articles

as shoe, clothing and leather goods. This situation affected the demand of tara either because

formulations of these articles do not consider wet-white as intermediate commodity, nor tara is

used for vegetable tanning but, mainly, quebracho.

Since 2003, the Consejo Nacional de la Cadena Productiva de la Tara (CONATARA) is the

platform for the cooperation and dialog between the economic agents in the tara commercial

chain and includes, also, institutions from administration and academy. The goal of

CONATARA is to generate specific competitive commitments to add value to the tara products

in its promotion in the international markets.

Production in Bolivia

Bolivia produces 200 tons of tara fruit per year. Exports go to Argentina, Uruguay and Chile,

and to Peru in informal commerce practices. Bolivian tara seeds are exported to Switzerland as

tara gum. There is a tendency to cultivate tara trees and to increase from the current 180 Ha to

2000 Ha in the coming years.

The two main regions of tara productions are Cochabamba and Potosi.

According to the ECOBONA-INTERCOOPERATON Regional program (2007) volume of tara

products, after transformation of tara pods, is 115 Tm, 100 tones of tara powder, 30 tons of

seeds and 21 tons of tara pods.

The Asociación Boliviana de Tara (ABT) was founded in 2007. Its members are ECOBONA,

BASFOR, the Agronomy Faculty of the University of San Simon in Cochabamba, ESFOR

(Forestry School), the University City of Sucre among other public and private institutions.

Production in Ecuador

Only two provinces in Ecuador, Imbabura and Chimborazo, produce tara fruit to the volume of

84 tons per year. A Spanish company, Cobad Export58

, purchases 75% of this production to be

58 Programa Nacional ECOBONA. Portal de Bosques Andinos (Date of consultancy December, 1, 2009) http://www.bosquesandinos.info/ECOBONA/TARA/TARABAJAIIIop.pdf

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transformed in 68 tons of tara products. Tara powder is exported to Spain (17 tons) and

commercialized to the tanneries in Ambato and Salcedo clusters. This company also produces

30 tons of seeds that are sold to Peru. The rest of 21 tons of tara pods are for local consumption,

mainly in artisanal leather.

The CONAPROG (Consorcio Nacional de Productores de Guarango) is an organization to

facilitate and promote the commerce of tara products.

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Annex 6. International leather production. Figures and statistics

The best comprehensive source of information on production and trade in the leather sector is

the “World statistical compendium for hides, skins and leather footwear”, produced every two

years by the Food and Agriculture Organization of the United Nations (FAO)59

.

The value of international trade of hides, skins achieves near 22,5 billion USD (average 2003-

2005).

Commodity Value Volume

Raw hides & skins 5.008,5 Million USD 2675 Kt

Wet blue, crust and finished

leather 17.477,7 Million USD 15.218 Million sq ft

There are no statistics to comprise the internal trading and information on production and trade

on a country basis will not be in the scope of this work. However, estimations from FAO

account for a world production of 6.319,6 thousand tones of bovine hides corresponding to 344

million pieces.

Bovine hides and skins account for 65% of the worldwide leather production, while sheep skins

15 %, Goat skins 9 % and pig skins and other 11%

According to FAO statistics, the worldwide leather production in 2006 was 22.700.5 million of

square feet (2.109 million of square meters). The main producer was China with a share of 29%.

Italy was the second producer with 9,5 %, India (7,6%) and Brazil (7,2%). Thirty countries

produced 91,7% of the global leather production.

Trends of production leather is quite stable in developed countries while increases in developing

countries as a result of the FAO statistics analysis:

59 Chief, Raw Materials. Tropical and Horticultural Products Service. Commodities and Trade Division (ESC). FAO.

Viale delle Terme di Caracalla. 0100 Rome. Italy. [emailprotected].

mailto:[emailprotected]

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The tanning industry in Europe (E27) reports revenues for 10.365 million euro with a value

added at factor costs of 1.975 million euro. There exist more than 3.000 tanneries, mostly in

Italy and employees 50.800 persons, according to Eurostat 2007 statistics..

Europe is the largest market for leather goods production with 13.924 enterprises, employing

108.500 persons and invoicing 12.097 million euro.

According to COTANCE60

President Johansson, “about 1 million jobs depend in Europe on the

sector and the EU market for leather and leather products is worth some 60 billion Euro.

European Tanners are at the root of this wealth and industry leaders at global level with some

15-17% of leather sales world-wide”.61

The chemical supply chain for the leather industry

The leather industry is a global industry which is affected by events occurring around the world

such as BSE and Foot & Mouth Disease crisis.

Leather chemical consumption is directly linked to the availability of hides (skins of animals

slaughtered for meat, primarily of bovine and ovine origin). The world trend is towards lower

red meat consumption per capita which is just about compensated by growth in the population

(1,7 to 1,9 per cent).

According to the “Frost&Sullivan “SWOT”analysis carried out in year 2000, the main aspects

are:

60 COTANCE: Confederation of National Associations of Tanners and Dressers of the European Community. The

European Leather Association: 3 reu Belliard, B-1040 Brussels, Belgium. Tel: 32 2 512 7703 – Fax: 32 2 512 9157.

[emailprotected]

61 COTANCE meets European Commission Vice-President Günter Verheugen.

http://www.euroleather.com/index.php?option=com_content&view=article&id=103:high -level-meeting-at-the-

commission&catid=29:trade&Itemid=53.

mailto:[emailprotected]

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Strengths:

Production of bovine and ovine hides as a result of meat consumption

Continuing demand for leather goods, from shoes, over upholstery through garment to bags,

belts, etc.

Weakness:

Strong dependence on raw hide availability and prices

Leather production causes environmental and safety issues and is restrained legislation.

Opportunities:

New technology and product development can resolve some environmental issues.

Threats:

The strong purchasing power of large end-users causes lower average prices for leather

chemicals.

Increased of usage of synthetic leathers or alternative materials.

However, due to this unique character, there are very few real drivers and restrains to the global

market.

Market trends and impact

Frost & Sullivan62

analyzes the European markets for four groups of specialty leather treatment

chemicals, including beamhouse chemicals, tanning chemicals, fatliquors and dyestuffs. The

report discusses market drivers and restraints, charts trends, and examines challenges that

market participants will face. It identifies areas for growth, provides expert forecasts, examines

end-user issues, monitors customer demands, and presents strategic recommendations. Profiles

of key industry participants are included. Comments have been modified by the author after

more than 30 years of experience in the leather chemical industry and focusing to the most

relevant and useful issues for the marketing of tara tannins.

Raw hide availability and prices affect leather production:

Most important restrains.

Outbreaks of BSE in EU countries other than the UK and FMD throughout the EU, as well as

Asia, South America and South Africa, have exacerbated the already deteriorated raw material

situation for tanner worldwide.

62 Frost & Sullivan is a global services enterprise with 1800 analysts, consultants, and visionaries that cover more tha n

300 markets and 250,000 companies from our 40+ global offices. www.frost.com.

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Facing a building demand for leather for the garment and upholstery segments, coupled with a

perceived diminishing of raw material drives up raw hide prices, which ultimately limits the

demand for leather as tanneries cannot pass the higher cost to their customers, e.g. fashion

designers, who will instead look for alternative materials.

Environmental and safety issues and legislation affect global competitiveness:

Important restrains, especially at regional level.

European Union and USA have strict environmental rules and regulations concerning waste

streams from tanneries, the necessity of waste management and ecological audits of the full

processing protocols.

The costs of effluent treatment, dust extraction, settling tanks for organics, chrome extraction

and personal safety equipment all add the cost of the production of leather treatment chemicals,

thus negatively affecting prices and competitiveness,

In developing countries, legislative safety issues associated with leather treatment chemicals are

generally no so extensive, giving the manufacturers in those countries a competitive advantage

with regards to pricing. However, safety and environmental conditions in these countries are

expected to improve in the coming years.

Relocation of leather producers to developing countries drives exports of leather chemicals and

increases competition in Europe and North America

Important restrains, especially at regional level

There is a general trend for end-users (primarily garment, shoes and furniture manufacturers) to

relocate to low labor cost countries. Leather production in these low cost countries is therefore

growing at a faster rate than elsewhere.

The access to the development resources is critical to most customers –they have primarily

“skilled labor” with too few technically qualified professional staff. Therefore, the ability to

offer the know-how of a full product range with service is becoming increasingly important in

securing loyalty.

Technology trends and product development trends emerging markets.

Continuing driver at global level..

In general, there is only a limited scope for technological break-thoughts (either product or

process); the base technologies are well established.

The major technology trends can be summarized as follows:

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Product substitution, such as the trend towards more environmentally friendly products, which

favors non-chrome and solvent-free products

Products that allow the use of less water.

On the customer side, process changes in tanneries (particularly automation) require suppliers to

be able to offer reliable and constant quality chemicals.

Raw material cost and source availability drives relocation of industry.

Driver or restrain at regional level.

To improve the overall economy of production of leather treatment chemicals a number of

producers have moved their production facilities closer to the raw material sources and the end-

user markets.

One stop shopping requirements of buyers.

Important competitive factor.

Similar to other industries leather treatment chemicals customers are seeking buyer friendly

solutions which require a full range of wet-end leather treatment chemicals and appropriate

technical service to solve specific customer queries.

Technical and customer service are key of success factors.

Important competitive factor

Customer service and high quality are pre-requisites for success in both mature and developing

regions.

Stabilizing prices.

Low impact driver

After continued decreases in prices for leather chemicals in the past this trend is expected to be

slightly in the near future duo to prices increases in raw material prices from the petrochemical

industry.

Trend to natural look limits usage of sinishes

Low impact restrain to the finishing sector.

The trend of the past to keep and emphasize the natural leather character is still going on.

Customer structure:

The overall customer structure of the leather chemical industry is very fragmented with very

few large tanneries and small family owned enterprises. The consolidation process among the

customers has been very limited.

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Leather chemicals. Total market size:

Frost & Sullivan estimated the total market size of leather treatment chemicals of 3.500 million

USD and more than 2 million tones, with annual grow rates of 1,4 to 2,3 %. These growing

rates not only depend on the total leather production. Approximately, upholstery, furniture and

auto, consumes around 30 % more chemicals that shoe leather production. Therefore, the mix of

leather articles has an impact on the consumption of chemicals.

Leather treatment chemicals can be segmented in specialty chemicals for beamhouse and wet-

end operations, excluding chromium salts and other basic auxiliaries, wet-end dyes and

finishing:

Leather treatment chemicals by value (Source Frost&Sullivant)

The figure is expressed in values and chemicals include specialty beamhouse chemicals,

specialty tannage chemicals and fatliquors. Approximately, half of the value of chemicals

corresponds to the value of tannins, either vegetable extracts or synthetic that in value can be

calculated 945 million USD.

In volume, the product type distribution defers considerably due to price differences between

them:

Leather treatment chemicals by volume (Source Frots&Sullivant)

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Trends by geographic region:

Leather treatment chemicals. Market by Regions (Source: Frost&Sullivant)

Europe (31%):

A slightly decreasing (-1% to 0%) is forecasted for the European leather market. This reflects

the decrease in raw leather treatment in Europe which involves specialty beamhouse, tanning

liquors and fatliquors products.

The most important markets in Europe are Italy, Spain and Germany.

Italy: is the only market that has survived the decline of western European leather industry. It

now accounts for around 10% of world leather production, and 50% of European leather

production. Italy produces shoes upper and upholstery leather and is famous for its highly

fashionable luxury garment and bag leathers which are susceptible to the unpredictable changes

seen in leather fashions.

Spain: is the second market in Europe. Due to the high quality of the skins (entrefino and

merino) garment leather was very much appreciated. But during the last years this production

has been relocated in Asian countries and clothing leather companies has become distributors

and designers of finished articles. Also, shoe leather has decreased considerable as shoe

manufactures have relocated the production plants to third countries. However, high quality

leather for leather goods has found its market niches with global luxury enterprises and

production has grown during the last years and it is maintained in a high level.

Germany: has the larges production of automotive and airplane upholstery leather in Europe

which, along with shoes upper and garment leather, makes up the majority of its production.

Auto sales affecting the demand of automotive upholstery in Germany have been suffering from

the financial crisis and consumers have been postponing the purchase of new cars. Therefore, is

a noticeable fall in leather production.

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North America (9%):

The North America market comprises USA, Canada and Mexico. The decline in the USA

market is partly compensated by shift to Mexico. This has contributed to move production from

low-medium quality leather for shoe to high standards leather for auto upholstery.

South America (16%)

The market also shows growing rates attributable to the increasing focus on automotive

upholstery.

Brazil: Stable after some years of uncertainness.

Argentina: Has suffered several internal crises due to the devaluation of the local currency but

has been stabilized. Argentinean tanneries focused on automotive leather but, during the last

two years have moved back partially to shoe and leather goods.

Asia market (44%)

China: is by far the largest leather producer of all kind of leather and continues growing due to

the low labor costs, government policies such as tariff reductions and investment incentives,

resource advantages in pig and sheep skins and that most of the global leather good

manufactures have been relocated in China.

India: is also a growing leather producer because of low labor costs, largest market for vegetable

tanning agents due to the availability of raw materials for vegetable tanning extracts and

growing domestic market for leather products.

Competition:

Traditionally, the leather treatment chemical suppliers have been multinational chemical

companies, based in developed countries and, most of them, in Germany. During the twentieth

century, these companies have supported all the knowledge and R&D activities related with the

leather process technology, among production and distribution. The advances of the modern

leather technology were linked to the research of new chemicals and the application of the

increasing knowledge of synthesis based on phenol, naftalen and polymer science. Also,

synthesis of dyes and fatliquors were fully applied during more the hundred years by the

chemical industry.

These companies actively were supporting the market offering a broad product range for the

complete process of leather making and technical services.

Since chemical specialties have become commodity products and leather industry has been

constrained by costs, the supply chemical chain has been spread with new competitor either

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product-focused (e.g. dyes manufacturers) or regionally focused (typically around tanneries in

Asia, Latin America and Italy).

Currently, the chemical suppliers can be considered as:

Global broad product range companies: Most of them with headquarters in Europe and

production sites distributed worldwide, mainly in developing countries, according their own

production strategies that do not consider the leather sector as priority. They use to have

daughter companies for marketing and distribution, sometimes, not located in leather production

clusters and, therefore, the use to have distributors for warehousing and often, invoicing and

servicing tanneries.

This figure shows the market share of BASF, Lanxess, Clariant, TFL and Stahl in the global

market and in the Specialty chemicals for beamhouse and wet-end operations where tara tannins

can be included:

The three market leaders, with revenues between 300 to 340 million euro do not exceed a

market share more that 10% and this shows that there is a very spread market with no a strong

leader position.

Global broad product range companies (TFL, BASF, Lanxess, Stahl, Clariant) account for

approximately 50 per cent of the total market.

Smaller competitors tend to be either product-focused (e.g. dyes manufacturers) of regionally

focused (typically around tanneries in Asia, Latin America and Italy).

Relevant trade related issues63

Registered Trade Marks in connection with Tara

The World Intellectual Property Organization (WIPO) is an agency of the United Nations,

established to develop and international intellectual property (IP) system. A trade mark is a

63 Tara Casealpina spinosa. Market Survey. Compiled by Swiss Import Promotion Programme (SIPPO) by ProFound –

Advisers In Development 2008/2009.

BASF 10% TFL

8%

Lanxess 10%

Clariant 10% Stahl

5%

Others 57%

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distinctive sign which identifies certain goods and those produced by specific person or

enterprise. Through a trademark, the owner is protected by having the exclusive right to use the

mark to identify goods.

In the databeses of OHIM and WIPO, no trade names were found for tannins from tara.

Howver, internet searches gave the following results: Ormotan™ from Silvatem, Tanosin from

Sochive, Lecosin from FGL, Fortan from A-Forte, Chimitan from Stefani Chimis, Floretan from

Codyeco and Chemitan from Chemipol.

Registered patents in connection with Tara

A patent search was done at ESP@CENET64

. Searching for the term tara in the titles and

abstracts of patents results in 222 patents in total.

Specifically, for the term “tara tannin” in the titles and abstracts of patents results in 9 patents.

Two results come from the searh of tara, selecting the European Classification conde C14C,

which is defined as “Chemical treatment of hides, skins or leather, e.g. tanning… compositions

for tanning”.

Tariffs, quotas and taxes

Tariffs on raw materials are generally low, in particular for ingredients originating in developing

countries. In order to support supplies from developing countries, the EU operates the

Generalized System of Preferences (GSP). Under the GSP scheme of the EU, imports from a

number of developing countries are admitted at the reduced tariff or at a zero tariff. Andean

countries belong to the GSPE group of counties.

A “EUR-1” form hat to be provided by the exporter to take advantage of the GSP tariff. The

EUR-1 form is a certificate of origin that is issued in preferential trading between the EU and

associate countries.

Packaging

Tara powder for the leather industry is packaged in polypropylene (PP) of polyethylene (PE)

bags (plastic) of 25 or 50 Kg.

Documents

Tara powder importers can demand a certificate of analysis (stating tannin content, solubility,

pH value in a certain solution). A packing list and a bill of lading are also required for the

transport of tara products.

64 http://ep.espacenet.com

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Cash-Against-Documents (CAD) and letters of credit are both used for payment of the goods.

Some importers prefer CAD, as it is a faster payment method for them.

Marking

The required marking mostly depends of the specific requirements of the importer. Information

that is often required includes date, supplier name, address, product name, net weight, if the

product is intended for food use, grade, recommended storage conditions. The information

should be in English and using EU measures (e.g. grams).

Labeling

Quality labels, such as a label for organic products could also be put on the packaging.

Sometimes, the attachment of certain documents can also be required. These may include a

certificate of analysis of a certificate of origin. Depending on the sourcing methods of the

importer, documentation might be important and elaborate of obsolete. Some importers prefer to

visit companies from which they have received interesting offers, while others prefer to gather

documentation which proves that the company can meet their requirements.

Prices

According to industry sources, the price for tara powder fluctuates approximately from € 0,70 /

kg FOB Callao, early in the 2007 and roses in 2008 to € 1,70 FOB / kg FOB Callao. During

2009, due to the lower production of leather articles, price went down again to € 0,76 / kg FOB

Callao.

The variation in price quotations has a large impact on the trade in tara powder. Industry sources

have become frustrated from the price fluctuations. Purchasing tara for a good price became

more difficult and long deliver times (4-5 months) combined with price fluctuations made tara

procurement a speculative business. Importers place very irregular orders, to profit most from

low prices.

The unreliable prices have resulted in the abandonment of the market by various traders.

Consequently, end-users have more difficult in sourcing tara powder and tend to switch to

alternative products. Industry sources have indicated that € 1,40 is the absolute price maximum

for importers. Tanneries will switch to other tannins when prices exceed the € 1,40 price level.

The substitution of tara, coupled with decreased demand, due to the financial crisis, has led to

sharp price decreases in the past year.

Tara products have to compete in established markets where margins are generally low. Prices

are based on actual costs of business operators (e.g. producers of processors). This kind of

price-setting is called cost-based or cost-plus pricing. Many suppliers compare their prices with

the prices of competitors and adjust their prices to improve their price performance ratio.

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However, one should bear in mind that competitive pricing requires extensive knowledge of the

products and services of competitors, as there are many value addiction activities which

influence prices.

For price information, it is possible to be obtained from reliable sources like Promperú, IMR

Internation, Online market places.

Quality requirements

In the leather manufacturing, variance of quality of the powder must be minimized as it can

affect the quality of final articles. Tanneries cannot adopt their formulations accordingly to the

lack of consistency of the suppliers and, therefore, the reliability of supplies is indispensable.

The main industrial requirements for tara are:

Tannin content: must be at least 50%.

Iron content: must not exceed 200 mg/Kg. Iron is a contamination from mills and shall be

minimized using stainless steel grinding machinery.

Color: must be as light as possible.

Mesh size: <200

Some traders in Europe supply tara tannin liquid form. The tannin of tara is extracted and

diluted with water and, in some cases, blended with other tannins or auxiliaries, formulated

ready to be used.

Marketing requirements, strategies and sales promotion

Critical requirement to supply EU markets is the ISO certification of the provider and

manufacturer.

Also, technical data sheet is required, containing product specification, product features such as

description of production process and applications fields and recommendations.

Marketing efforts need to focus on restoring confidence to importers. Prices must become more

stable and delivery times have to become shorter. For a sustainable trade in tara, profit-making

has to be based on long-term business relationships instead of short-term selling to the highest

bidder. Contract-farming offers a safe solution for both suppliers and buyers. Note, however,

that not all buyers are willing to make long-term commitments.

The price fluctuation of the past years is strongly related to the availability of tara on the global

market. Stocking tara can be an effective tool to stabilize prices. Stocking has to start a

minimum price levels while stocks must be sold at maximum price levels.

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The value of international trade in hides, skins and leather footwear

average 2003-2005 (Million US Dollars)

Developing

countries

Developed

countries

World

Raw hides and skins 598.4 4,410.1 5,008.5

Wet blue, crust and Finished leather 9340.0 8137.7 17,477.7

Leather footwear 13,990.9 17,347.7 31,338.6

Total 23,929.3 29,989.5 53,824.8

Meat from Cattle, Sheep and Goats 5,264 18,841 24,105

Rubber 6,859 162 7,022

Cotton 3,086 6,122 9,208

Coffee 6,738 2,869 9,607

Tea 2,567 691 3,258

Rice 5,779 1,231 7,01

Sugar 6,93 4,222 12,281

Source FAO

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Production of bovine hides (million pieces)

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

WORLD 314.8 316.8 319.2 315.6 321.3 330.0 329.8 333.0 335.2 344.0

Developing countries 190.5 195.5 200.2 201.2 205.7 213.0 214.5 224.9 226.1 232.8

Developed Countries 124.3 121.2 118.9 114.4 115.6 117.0 112.3 108.1 109.0 111.2

Latin America 62.7 64.8 66.1 66.1 67.4 69.4 71.7 74.3 75.2 77.1

Africa 19.4 20.0 19.6 20.1 21.2 21.4 21.5 21.9 21.9 21.9

Near East 13.1 12.5 12.8 12.6 12.7 12.8 13.0 12.8 13.0 13.1

Far East 95.6 98.4 101.2 102.4 105.6 107.4 111.8 115.8 115.9 120.6

Other Developing 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

North America 40.9 41.6 41.4 40.3 40.7 40.1 38.7 36.6 38.1 38.4

Europe 37.0 36.4 35.0 33.9 34.3 33.5 32.8 32.0 31.1 32.0

Former USSR 29.7 27.0 26.4 24.3 24.6 26.0 24.7 22.6 23.2 23.2

Oceania 13.1 12.6 12.0 12.4 12.1 13.3 12.9 12.7 12.2 13.0

Other Developed 4.2 4.2 4.2 3.5 4.0 4.0 4.2 4.3 4.5 4.6

Source: FAO

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Production of bovine hides (000’s Tonnes)

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

WORLD 5722.9 5774.5 5814.4 5863.2 5783.9 5870.3 6103.5 6059.4 6098.8 6159.3 6319.6

Developing

countries

2885.5 3019.0 3112.9 3209.7 3230.7 3284.2 3499.4 3551.1 3681.4 3709.7 3821.9

Developed

Countries

2837.4 2755.6 2712.1 2662.7 2562.5 2591.1 2610.0 2508.2 2417.4 2449.6 2497.7

Latin America 1238.0 1303.8 1380.5 1443.4 1454.6 1432.9 1585.2 1566.6 1632.3 1653.7 1696.3

Africa 244.0 260.2 269.5 262.4 268.3 281.3 284.5 285.6 291.7 291.1 292.7

Near East 201.6 205.2 198.8 203.9 201.6 193.1 201.7 207.3 205.4 208.8 211.2

Far East 1171.7 1220.1 1260.5 1296.9 1320.4 1369.7 1419.6 1488.4 1549.0 1553.1 1618.5

Other

Developing

3.0 3.0 2.9 3.0 3.0 2.9 3.0 3.0 3.0 3.0 3.2

North America 1032.7 1011.1 1027.6 1024.1 995.9 1007.1 993.2 930.9 902.5 939.1 948.6

Europe 879.9 858.5 840.2 810.3 789.8 799.9 789.5 781.5 761.7 742.8 764.2

Former USSR 618.8 563.7 516.7 505.3 460.4 467.9 494.6 469.4 428.3 438.8 439.1

Oceania 221.8 239.2 231.1 219.2 227.4 221.2 241.9 233.0 230.3 229.6 244.3

Other Developed 84.2 83.1 85.9 93.7 81.3 89.9 89.5 93.1 94.5 99.2 101.6

Source: FAO

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Annex 7. General overview of making leather from raw hides

Beamhouse:

Sorting: On receipt, hides and skins may be sorted into several grades by size, weight, or

quality. Hides are also sorted by sex.

Trimming: Some o the edges (legs, tails, face, udders, etc.) of the raw hides and skins can be cut

off.

Curing & storing: Curing is a process that prevents de degradation of hides and skins from the

time they are flayed in the abattoir until the process is the beamhouse are started. When the raw

material cannot be processed immediately (“green”) it must be cured. The methods for curing

for long-term preservation are: salting, brining, drying and salt drying. Methods for short-term

preservation are cooling, using crushed ice or refrigerated storage and biocides. Hides and skins

are generally stored as they are received by the tannery on pallets in ventilated or air

conditioned and/or cooled areas, depending on the method of curing chosen. From storage the

hides and skins are taken to the beamhouse.

Soaking: Soaking is carried out to allow hides and skins to re-absorb water, to clean and to

remove interfibrillary material from them. The soaking methods depend on the state of the

hides. The process is mostly carried out in two steps: a dirt soak to remove the salt and dirt and

a main soak. The process is carried out in processing vessels, such as mixers, drums, paddles or

pits. The duration of soaking may range from several hours to a few days. Depending on the

type of raw materials, soaking additives can be used such a surfactants, enzyme preparations

and bactericides.

Unhairing & liming of bovine hides: The function of liming and unhearing is to remove hair,

interfibrillary components and epidermis and to open up the fiber structure. Hair removal is

performed by chemical and mechanical means. The keratinous materials (hair, hair roots,

epidermis) and fat are eliminated from the pelts mainly with sulphides (NaHS or Na2S) and

lime. Enzymatic preparations are sometimes added to improve the performance of the process.

The process of liming and unhearing can be carried out in process vessels such as drums,

paddles, mixers or pits.

Pinting & liming of sheepskins: The aim of painting is to bring about the breakdown of the wool

root within the skin so that as much undamaged wool fiber as possible can be pulled easily from

the pelt. Paint, generally, consisting of a mixture of sodium sulphide and lime, is applied to the

flesh side of the skin and left for several hours. Application of the paint can be through a

spraying machine or manually. After several hours the wool can be “pulled” from the skin,

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either manually or mechanically. After pulling, the skins are limed in process vessels, with the

same purpose as the liming of bovine hides. Wool-on skins are not painted, unhaired or limed.

Fleshing: Is a mechanical scraping off of the excessive organic material from the hide

(connective tissue, fat, etc). The pelts are carried through rollers and across rotating spiral

blades by the fleshing machine. Flashing can be carried out prior to soaking, after soaking or

after pickling.

Splitting: By mechanical splitting the thickness of hides and skins is regulated and they are split

horizontally into a grain layer and, if the hide is thick enough, a flesh layer. Splitting is carried

out on splitting machines, fitted with a band knife. Splitting can be done in limed condition or in

the tanned condition.

Tanning operations:

Deliming: To remove residual lime from the pelts and to take them to the optimum condition for

bating. This involve a gradual lowering of the pH (by means of washing and addition of

deliming chemicals), an increase in temperature and the removal of residual chemicals and

degraded skin components. Generally, deliming is performed in a processing vessel such as a

drum, mixer or paddle.

Bating: Is a partial degradation of non- collagenic protein achieved by enzymes to improve

grain of hide and the subsequent run and stretch of leather. In this process the rest of the

unwanted hair roots and scud can be removed.

Degreasing: Excess grease must be eliminated from fatty skins (sheep, pig) to prevent the

formation of insoluble chrome-soaps or prevent the formation of fat spots at later stage.

Degreasing is most relevant in processing sheep skins, where the natural fat content is about 10-

20% on dry weight. The nature of this fat makes it difficult to remove because of the presence

of cerides and a high melting temperature. The three methods commonly used for degreasing

are: with organic solvent and non-ionic surfactant, in aqueous medium with non-ionic surfactant

and in solvent medium.

Pickling: Is carried out to reduce pH of the pelt prior to mineral tanning and some organic

tannages. The choice of the exact pickling parameters depends on the subsequent tanning step.

Very often is carried out in the tanning liquor; however, pickled pelts can be traded, especially

sheepskins, using fungicides to protect them from mould growth during storage.

Tanning: In the tanning process the collagen fiber is stabilized by the tanning agents such that

the hide is no longer susceptible to putrefaction or rotting. In this process the collagen fibers are

stabilized by the cross-linking action of the tanning agents. Furthermore their dimension

stability, resistance to mechanical action and heat increase. Various agent can be categorized in

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three main groups: mineral tannins, vegetable tannins, alternative such as syntans, aldehydes,

oil… Chromium and vegetable tanning agents are the most commonly used tanning agents.

Draining, samming and setting: After tanning, the leathers are drained, rinsed and either horsed

up to age, or unloaded in boxes and subsequently sammed to reduce the moisture content prior

to further mechanical action, such as splitting and shaving. The setting our operation can be

carried out to stretch out the leather. There exist machines which combine the samming and

setting action. After samming and setting, hides and skins can be sorted into different grades

after which they are processed further or sold on the market.

Shaving: The shaving process is carried out to achieve an even thickness throughout the

skin/hide, and it can be carried out on tanned or crusted leather. Shaving is carried out where

splitting is not possible or where minor adjustments to the thickness are required.

Post-tanning operations:

Post-tanning involves neutralization and washing, followed by retanning, dyeing and

Fatliquoring, mostly done in a single processing vessel. At this stage of the process, specialist

operations may also be carried out to add certain properties to the leather such as water

repellence or resistance, oleophobing, gas permeability, flame retarding, abrasion, anti-

electrostatics, etc.

Neutralization: Is the process by which the tanned hides are brought to a pH suitable for the

process of retanning, dyeing and Fatliquoring.

Bleaching: Vegetable tanned skins and leathers with wool or hair may need to be bleached in

order to remove stains, or to reduce the coloring in the hair, wool or leather prior to retanning

and dyeing.

Retanning: The retanning process can be carried out with the following objectives:

To improve the feel and handle of the leathers

To fill the looser and softer parts of the leather in order to produce leathers or more uniform

physical properties and with more economical cutting value to the customer

To assist in the production of corrected grain leathers

To improve the resistance to alkali and perspiration

To improve wetting back property of the hides which will help the dyeing process.

A wide variety of chemicals can be used for the retannage of leather. They can generally be

divided into the following categories: vegetable extracts, syntans, aldehydes, mineral tanning

agents and resins.

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Dyeing: The dyeing process is carried out to produce level colors over the whole surface of each

hide and skin and exact matching between hides in a commercial pack. Typical dyestuffs are

water-based acid dyes.

Fatliquoring: Leathers must be lubricated to achieve product-specific characteristics and to re-

establish the fat content lost in the previous procedures. The oils used may be of animal or

vegetable origin, or might be synthetics based on mineral oils.

The retanned, dyed and fatliquored leather is usually washed before being horsed up (piled on

“horses”) to rest.

Drying: The objective is to dry the leather whilst optimizing the quality and area yield. There is

a wide range of drying techniques and some may be used in combination. Each technique has a

specific influence on the characteristics of the leather. The most used drying techniques include

samming, setting out, hang drying, vacuum drying, and toggle drying. Generally samming and

setting out are used to reduce the moisture content mechanically before another drying

technique is used dry the leather further. After drying, the leather may be referred as curst. Crust

is a tradable intermediate product.

Finishing:

The overall objective of finishing is to enhance the appearance of the leather and to provide the

performance characteristics expected of the finished with respect to: color, gloss, handle, flex,

adhesion, rub fastness, as well as other properties including extensibility, break, light and

perspiration fastness, water vapor permeability and water resistance as required for the end use.

Generally, finishing operations can be divided into mechanical finishing processes and applying

a surface coat.

Mechanical finished processes: a wide range of mechanical finishing operations may be carried

out to improve the appearance and the feel of the leather. The following list includes, among

others, commonly used mechanical finishing operations:

Conditioning: optimizing the moisture content in leather for subsequent operations

Staking: softening and stretching of leather

Buffing/de-dusting: abrading of the leather surface and removing the resulting dust from the

leather surface.

Dry milling: mechanical softening

Polishing

Plating / embossing: flattering or printing a pattern into the leather.

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These operations may be carried out before or after applying a coat, or between the applications

of coatings.

Applying a surface coat: The purpose of applying a surface coat is:

To provide protection from contaminants (water, oils, soil…)

To provide color either to modify dyed color or reinforce that provided by the dyes, to even the

color or to disguise defects.

To provide modifications to handle and gloss performance

To provide attractive fashion or fancy effects

To meet other customer requirements

There is a wide range of application methods each of which has its advantages and

disadvantages. A combination of methods can be used to achieve the desired effect on the

finished product. In principle, the following types of application methods can be distinguished:

Padding or brushing the finishing mix onto the leather surface

Spray coating which involve spraying the finishing material with pressurized air in spry

cabinets.

Curtain coating, which is passing the leather through a curtain of finishing material

Roller coating, which is an application of finishing mix through a roller

Transfer coating, which is the transfer of a film/foil onto leather previously treated with an

adhesive.

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Annex 8: Environmental considerations for the leather industry

This table expresses the input and output overview for a conventional (chrome tanning) process

for bovine salted hides per ton of raw hide treated. The quantities and qualities of emissions and

waste produced by tanneries strongly depend on the type of leather processed, the source of

hides and skins and the techniques applied.

Environmental concerns in a tannery include waste water, solid waste, air pollution, soil

protection and safety aspects. The releases potentially contain toxic, persistent or otherwise

harmful substances.

Most of the steps of the tannery’s operation are performed in water. Consequently waste water

effluent is one of the major concerns in tanneries. The characteristics of waste water are a high

chemical and biological oxygen demand, high salt content and toxic releases. The table bellow

shows the consumption level of the main process chemicals, tanning agents and auxiliary

chemicals for a conventional tanning process for salted bovine hides.

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A further aspect to be aware of in the tanneries is the potential hazard to human health and the

environment for handling, storing, transporting and packaging of chemicals.

When effluents discharge to water treatment plants, either municipal or plants operated for large

tanning complexes, it is produced a high amount of sludge, about 5 to 10% of the total volume

of effluent being discharged. The settle sludge resulting is normally in the form of a liquid with

a solids content of 3-5% dry solids. Typically, sludge are dewater to have a dry matter content if

25-40%.

For sludge and other residues further re-use and recycling options exists. The viability of these

options is strongly dependent on the composition of the residues. Landfilling of wastes with

high organic content and toxic substances is increasingly coming under pressure in many

countries. Other strategies include reduction measures by means of recycling, composting,

biogas production or materials/energy recovery. However, an average of more than 80% of

these solid residues and sludge contain chromium.

Probably, the most debated issue with regards to the leather industry impact in the environment

is the chrome tanning, thus the utilization of chromium (III) salts. They are used in the tanning

industry and its toxicity shall not be confused with chromium (VI). Hexavalent chromium is

known to be a skin irritant and thought to be carcinogen.

Despite toxicity of chromium (III) salts is similar to the table salt, there are concerns because

potential oxidation, either in leather articles, effluents after chrome tanning or solid wastes. It is

know the effect of certain fatliquors and other chemicals to oxidize tanned leather, but also,

some other that prevent such formation. Polyphenols, contained in vegetable tannins have

shown anti-oxidation properties.

Due to the fact that chromium has been under pressure from regulatory authorities, and other

collectives, some leather users are beginning to demand the use of alternative tanning agents,

such as glutaraldehyde, aluminum and vegetable tannins. In any case, nowadays, chrome

tanning is the most efficient and versatile tanning agent available and it is relatively cheap.

The amount of chemicals used varies significantly with the specification of the final product, the

pelts treated and the process chosen. Figures for consumption of chemicals can therefore only

be given within a broad range. Besides the main process chemicals, a great variety of substances

is used for auxiliary process purposes. For reasons of workplace health and safety, some barely

soluble agents are applied as aqueous suspensions or dispersion, which may have to be

stabilized with auxiliaries, thus adding even further to the number of chemicals used.

It is common for tanneries to use more than 300 different chemicals in the lather making

process. The potential impact of chemicals will depend of many factors:

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The selected chemicals

The medium in which it is released (solid waste, atmosphere, effluent, soil…)

The actual concentration received by the environment. It should be noted that the

quantities in the waste water are not strictly a function on the input quantities. Some

agents are almost totally absorbed, react in the process or are precipitated in the waste

water treatment.

Transformation of the chemicals due to chemical and biological process before and after

discharge o the environment. The substances might react during the process or with

other constituents; or they are degraded in the waste water treatment plant; they can also

be distributed to different outlets of a factory.

Continuous or batch discharge.

Characteristics of the receiving environment. For example in a water course, essential

factors are: the stress of organisms due to other constituents; inhibitory or synergetic

effects due to other chemicals; flow characteristics; light and temperature.

Chemical consumption %

Standard inorganic (without salt from curing, acids, bases, sulphides, ammonium-

containing chemicals)

40

Standard organic, not mentioned bellow (acids, bases, salts) 7

Tanning chemicals (chrome, vegetable and alternative tanning agents) 23

Dyeing agents and auxiliaries 4

Fatliquoring agents 8

Finish chemicals (pigments, special effect chemicals, binders and crosslinking

agent)

10

Organic solvents 5

Surfactants 1

Biocides 0,2

Enzymes 1

Others (sequestering agents, wetting agents, complexing atents…)

Total 100

Consumption of chemicals in leather processes (Source Bref)

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Annex 9: The application of the vegetable tannins in the leather

industry

Vegetable tannins are niche products, compared to chrome salts. The main advantage of

vegetable tannins is that they are supposed more environmental friendly. With increasing strict

EU legislation regarding waste and waste water treatment, vegetable tannins offer specifically

interesting solutions for tanneries aiming to reduce their pollution.

Tannins displace water from the interstices between the protein fibers in the skin and cements

the fibers together, preserving its flexibility and making it resistant to rot. Vegetable tannins get

deeply and uniformly dispersed in the hide, resulting in roundness and feel properties.

Most of the plants contain tannins. However, only a small number of them have shown true

value as commercial products in the vegetable tanning. Currently, most of the commercial

tannins are offered as extracts from different parts of the plants:

Bark: pine and mimosa

Wood: Chestnut, quebracho

Leaves: Sumac

Fruits: Valonia, tara

Quebracho:

Quebracho is the most important and most widely used extract in the tanning industry.

The tannin is extracted from the wood of the Qhebrachia lorentzii, a tree that grows in South

America, predominantly in Argentina. It is a very slow-growing tree, taking approximately one

hundred years to reach maturity.65

The extract contains about 63-70% good quality tannins,

condensed or catechol type.

The natural tannin of quebracho is soluble in hot water but condensates when it is cooled. In this

stage, having a very low content of non-tannins, is used to obtain heavy leather articles, such

sole leather. Its pH is higher than 6 and has an average molecular weight of 2400. The leathers

tanned with quebracho trend to have a red color.

In order to increase its solubility, the extract needs to be clarified by treatment with bisulfite.

This reduces its astringency and decreases the insoluble matter but increases the non-tannin

content. Sulfited quebracho has a pH higher that 6 and average molecular weight between 700

and 800. The strong tendency to fix with the hide is reduced and, therefore, the tannin penetrates

easily and a softer leather, but emptier, is obtain. The color of the tanned leather is quite light.

65 Thomas C. Thortensen. Practical leather technology. Robert E. Krieger Publishing company, Malabar. Florida. USA. Third Edition. 1985. Page 149.

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Mimosa:

Mimosa, wattle extract, is the second most important extract, coming from the bark of the trees

of the various acacia species, but principally from Acacia mollissima. The extracted tannin is

catechol type. The plant is originally from Australia, but is grown commercially in South

Africa, an in a small quantity in Brazil.

It contains about 60 % of tannins and 18-20% of non-tannins. The extract contains some sugars

and has a very small amount of insolubles. Its average molecular weight is between 1600 and

1700.

For leather articles manufacturing, mimosa extract has low astringency, thus good penetration

and is often used in the re-tannage of upper leathers.

Leathers tanned with mimosa extract have a beige-yellow color, lighter than the treated with

quebracho. However, oxidizes easily when articles are exposed to the light and color turns to

violete.

Chestnut

The chestnut wood extract is obtained from the chestnut tree Castanea dentate, the grows in the

United States, France and Italy, among other countries in the Mediterranean bank. It was the

most important source of vegetable tannins until sources of chestnut wood became too

expensive due to the blight and the cost to obtain the wood.

The tannin is hydrolysable and has a natural pH value of about 3 in solution and a molecular

weight of 1500. Due to its astringency, chestnut extract is sweeten with reductive and alkaline

matters, until pH reaches 4,5 value.

Leathers treated with chestnut have a better light fastness that mimosa and quebracho and have

a certain waterproof behavior. Color trends to be between light red brown and green.

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Annex 10: Equipment for experimental tests

Photo 26: Fave drums, stainless steel, 500x2mm (DxL).

Photo 27: Simplex drums, stainless steel, 4 T.D.F.

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Annex 11: I am a tree and you too

YO SOY UN ARBOL, Y TU TAMBIÉN

AMARU CHOLANGO. QUITO. 1996.

Ahí yace muerto

Sus manos no alcanzan el cielo y

Sus raíces no alcanzan

El fuego de la tierra.

Lo tomo con mis manos

para quemarlo

Lo alzo

Lo tomo de nuevo y muchas veces más.

Con mis manos

lo lleno de ternura

al fin

Lo bautizo con fuego.

¡Ahora vive él!

¡Ahora él es!

Ahora es arte.

Ahora es más que un árbol.

¡Ahora él es todos los árboles!

A través de sus venas no corre savia

corre leche

del tiempo. El silencio

There lies dead

His hands do no reach the heaven

His roots do not reach

the fire of the earth.

I take him in my hands

to burn him

I leave him.

I take him and many times.

With my hands

I give him tenderness

at the end

I baptize him with fire.

Now he lives!

How he is!

Now he is art.

Now he is more than a tree.

Now he is all the trees!

Through his veins runs no sap

runs milk

of time. The silence.

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FAQs

What are tannins for tanning? ›

Plant-based extracts and tanning

Tannins are gathered from many types of trees and plants and can be present either in bark, leaves, wood or even in fruits and roots. Only tannins are able to give tanned leather these unique characteristics that make them so special and so easily distinguishable.

What are the ingredients in veg tanning? ›

Raw materials used for vegetable tanning are natural tannins, available in liquid or powder form, obtained from a different part of plants including woods, barks, fruits, fruit pods, and leaves. The most common tannins are obtained from: Chestnut wood (Castanea sativa) Quebracho wood (Schinopsis lorentzii)

What are vegetable tannins examples? ›

Various types of vegetable tannins have distinct effects. The effects of different types of vegetable tannins including black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were evaluated [62] . ...

What plants are high in tannins? ›

Complex tannins and condensed tannins are the most common and easy to extract from legumes, trees and shrubs; Gallic tannins are commonly found in gallnuts, lacquer leaves and cotinus leaves, while ellagic tannins are commonly found in oaks, blackberries and pomegranates.

Do tannins tighten skin? ›

Remember that tannins are astringents that tighten pores and draw out liquids. Witch hazel (Hamamelis virginiana) is a source of tannin used in a number of skin care products.

What do tannins do to your body? ›

Tannins have also been reported to exert other physiological effects, such as to accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses. The dosage and kind of tannins are critical to these effects.

Is Veg tan leather real leather? ›

Vegetable tanning is one of the main leather production methods in use today: approximately 10% of all leather is vegetable tanned. This technique involves using natural vegetable tannins to alter the protein structure of the hide, causing it to become leather.

Is Veg tan leather laser safe? ›

Effectively, as long as you use trivalent-chromium chrome-tanned leather patches (or oil-tanned or veg-tanned leather patches), you don't really need to equip your laser machine with an air exhaust system.

Why are carrots good for tanning? ›

Any extra beta-carotene is then either stored in the liver and fat tissue, excreted through poo, or removed via sweat glands in the outer layer of the skin. This is when the orange skin “tan” can happen. In medicine, this is called carotenoderma.

What food is high in tannins? ›

Humans consume a number of foods containing considerable amounts of dietary tannins. Tannins are found in a huge variety of plants, including legume seeds, cider, cereals, cacao, peas, some leafy and green vegetables, coffee, tea, and nuts (Lochab et al., 2014; Suvanto et al., 2017; Fraga-Corral et al., 2020).

Which fruit has the most tannins? ›

For tannins in general, their contents are relatively high in fruits such as persimmon, pomegranate, grape, cashew apple, guava, chokeberries, blackberries, raspberries, apple, banana, etc [25,26, 35, 36].

Is coffee high in tannins? ›

There is a bit of good news in all this: coffee may not be the worst culprit of these drinks. When a group of researchers compared the tannin content of coffee with tea, they discovered that green coffee contains around 0.7% by weight in tannins, roasted coffee around 1.8%, and tea up to 3.7%.

What are the side effects of tannins? ›

The FDA has asked for more studies. In large amounts, tannic acid can cause side effects such as stomach irritation, nausea, vomiting, and liver damage. Regular consumption of herbs with high tannin concentrations seems to be associated with an increased chance of developing nose or throat cancer.

What spices are high in tannins? ›

Tannin-touting herbs include licorice, mint, rosemary, coriander, and sage. Many spices also contain tannins and other phenolic compounds; two common ones are cinnamon and cloves. Others include ginger, black cumin seeds, and piripiri.

Which tea is very high in tannins? ›

Black teas contain particularly high levels of tannins, two of which are thought to be responsible for the distinctive color of black tea.

What is the side effect of tannins? ›

The FDA has asked for more studies. In large amounts, tannic acid can cause side effects such as stomach irritation, nausea, vomiting, and liver damage. Regular consumption of herbs with high tannin concentrations seems to be associated with an increased chance of developing nose or throat cancer.

How do tannins make you feel? ›

Essentially, tannins add bitterness and astringency. These two qualities are evident when you're drinking a young wine, making it feel harsh on your tongue and drying out your mouth. The taste can be shockingly, mouth-puckeringly astringent, or “green.”

What is the disadvantage of tannins? ›

Tea tannins may cause nausea, especially if consumed on an empty stomach. They may also hinder your body's ability to absorb iron from certain foods. To get the most benefit from tannin-rich tea, consume it separately from foods containing iron, and make sure you drink it in moderation.

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