ABSTRACT
Tannin chemically stabilizes hides and skins against bacterial attack, transforming the
raw material into leather. In the search for alternative sources of tanning materials, only
a few of these materials have shown true value as commercial products in the vegetable
tannin field. The negative effect of trivalent chromium both to the tanners and the
environment has increased the search for alternative tanning materials which could be
eco-friendly.Pods of Caesalpinia coriaria (DD) and husk of Parkia clappertoniana
(PC) tannins were extracted using Procter apparatus and Soxhlet apparatus. The crude
extracts of both DD and PC were purified using gel permeation chromatography and
modified using sodium bisulphite and pancreatic trypsin .The modified tannins were
characterized using UV-VIS, FT-IR, TLC, sorptive capacity and binding ability. The
modified tannin and 16different tannin ratios of DD and PC were used in the tanning of
goat skin. The result of the qualitative and quantitative assessment placed DD to be
hydrolysable tannins with 47% pure tannins and PC to be condensed tannins with
42.33% pure tannins. This shows that the two plants have more than 10 % threshold
tannin content required for commercial extraction. The TLC of methanolic extract of
DD and PC using glacial acetic acid indicated the components of the tannins to be
3,4,6,tri- O- Galloyl-D-glucose, tannic acid ,pyrogallol and gallic acid for DD, and
catechol, gallic acid for PC. The ultraviolet visible absorption spectra for the modified
PC and DD was found to be lower than that of the unmodified. A peak for modified PC
was found to be at 460 nm while the unmodified was at 480 nm. The use of sodium
bisulphite to modified PC and DD shows a good effect by reducing the large molecular
weight of PC and increasing the reactivity of PC and DD. The use of pancreatic trypsin
was found to be suitable for PC. PC extract has the best properties in terms of binding
and sorption by 45.50% and 95% respectively at 10% sodium bisulphite followed by
vii
DD extract which has 15.33% and 46% binding and sorptive capacity respectively at 10
% sodium bisulphite. On the contrary, DD showed no significant change as the
concentration of pancreatic trypsin increased. Also, the binding capacity of PC
increased from 12% to 25% with the increase in the concentration of pancreatic trypsin
from 2% to 8%,whereas DD showed no significant change. The pH (4.03) of DD could
inhibit enzyme activity. The FT-IR spectra of modified sample of DD gave similar
absorption bands with the unmodified except with the removal of three bands (1624.5,
965.4 and 670.9 cm-1) which arose from C = O, C = CH and Ar-H bending out of plane.
Also, PC spectra gave similar bands except the presence of C – H stretching in aromatic
methoxyl groups (2926.0; 84.933 cm-1) in the modified which was not found in the
unmodified. This could be attributed to the break of bond or hydrolysis of the high
molecular weight of the tanning by the reagent (sodium bisulphite).The liming process
was optimized using Box Behnken design The quadratic polynomial model was used to
characterize the liming process. The plots showed that these independent variables
significantly influenced the liming conditions. In this work, it was established that the
best condition for the liming process was found to be: 1.5 %, lime concentration, 20 hr
and 300 % water. The quality of the leathers was determined according to the
International Union of Leather Technologists and Chemist Society (IULTCS) official
methods. The values obtained, met the standard requirement for vegetable leathers. A
careful selection of the percentage liming used in the liming process and Fatliquoring
of the tanned leather with vegetable tannins such as DD and PC with modification
using sodium bisulphite and pancreatic trypsin could be used to produce a quality
leather and serve as a substitute for chrome tanning or as complementary, since it is
possible to get Shrinkage Temperature of 90 oC.
viii
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of Contents viii
List of Figures xii
List of Tables xiv
List of Plates xv
Appendix I xvi
Definition and Glossaries xvii
List of Abbreviations and Symbols xxi
CHAPTER ONE
1.0 INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of the Research Problem 5
1.3 Significance of the Study 8
1.4 Aim and Objectives 8
CHAPTER TWO
2.0 LITERATURE REVIEW 10
2.1 Origin of the Parkia clappertoniana Plant 10
2.1.1 Scientific Classification of Parkia clappertoniana 11
2.1.2 Economic Importance of Parkia clappertoniana 11
2.1.3 Morphology of the Plant 14
2.2 Origin of the Caesalpinia coriaria Plant 18
2.2.1 Classification of the Plant 19
2.2.2 Economic Importance of Caesalpinia coriaria 20
2.3 Vegetable Tannins 24
2.3.1 The Vegetable Extracts Fractions 26
2.3.2 Uses of Tannins 26
2.3.3 Tannin Classification 27
2.3.4 Classification of the Tannins Based on their Structural Properties 29
ix
2.3.5 Hydrolysable Tannins 29
2.3.6 Complex Tannins 32
2.3.7 Condensed Tannins 33
2.4 Significance of Tannins in Plants 36
2.5 Biological Activities of Tannins 37
2.6 Enzymes in Leather Industry 37
2.7 Sulphitation 38
2.8 Structure and Function of Hide and Skin 39
2.9 Goats Skins 44
2.10 Mineral Tanning 44
2.11 Vegetable Tanning 45
2.11.1 Sorptive Ability and Binding Capacity of Collagen 47
2.12 Leather Processing 49
2.12.1 Beam House Operation 49
2.12.2 Soaking 49
2.12.3 Unhairing 50
2.12.4 Liming 51
2.12.5 Deliming 54
2.12.6 Bating 55
2.12.7 Pickling 55
2.12.8 Tanning 55
2.13 Leather 56
2.14 Uses and Applications of Vegetable Tanned Leathers 56
2.15 Instrumentation for UV-VIS and FT-IR Spectrophotometer 57
CHAPTER THREE
3.1 MATERIALS AND METHODS 63
3.1 Sample Collection 63
3.2 Extraction of Tannins 63
3.2.1 Soxhlet Extraction 63
3.2.2 Proctor Extraction 64
3.2 Test for the Presence of Vegetable Tannins 64
3.3 Determination of Tanning Strength of the Extracts 65
3.3.1 Determination of Moisture Content 65
3.3.2 Determination of Total Solids 65
x
3.3.3 Determination of Total Soluble 66
3.3.4 Determination of Total Insoluble 66
3.3.5 Determination of pH of the Extracts 66
3.4 Chromatographic Separations of Tannins 67
3.4.1 TLC of Condensed and Hydrolysed Tannins 67
3.4.2 Column Chromatography 67
3.4.3 Purification of Tannins 68
3.5 Preparation of the Samples for FT-IR 69
3.6 Sorptive Ability and Binding Capacity with Hide Powder 69
3.7 Determination of Tannins 70
3.7.1 Official Shake‘s Method (SLTC, 1996) 70
3.7.2 Measurement of Total Phenolics and Tannins using Folin-ciocalteu
Method 72
3.7.3 Determination of Condensed Tannins (Proanthocyanidins) 73
3.7.4 Gallotannin Determination by Rhodanine Acid 74
3.7.5 Determination of free Gallic acid 74
3.7.6 Determination of Gallic acid present in free and in gallotannin Forms 74
3.7.7 Preparation of Gallic acid Solution 75
3.7.8 Determination of Stabilization Time between Ferric chloride
and the sample solution 75
3.8 Tanning Procedure 75
3.9 Physical Analysis of the Tanned Leather 77
3.9.1 Shrinkage Temperature Determination 77
3.9.2 Measurement of Thickness 78
3.9.3 Measurement of the Apparent Density of Leather 78
3.9.4 Measurement of the Resistance to Compression 78
3.9.5 Measurement of Indentation Index 79
3.9.6 Measurement of Tensile Strength 79
3.9.7 Percentage Elongation at Break 79
3.9.8 Lastometer Determination of Grain Crack Properties of Leather 80
3.9.9 Measurement of Water Vapour Absorption 80
3.9.10 Measurement of the Absorption of Water 80
3.9.11 Measurement of Water Vapour Permeability 81
3.10 Chemical Analysis on Leather 82
xi
3.10.1 Preparation of Leather Sample 82
3.10.2 Determination of Ash Content 82
3.10.3 Determination of Fat Content 82
3.10.4 Determination of Total Matter Soluble in Water 83
3.10.5 Determination of Hide Substance 83
3.11 Hide Powder Preparation 84
3.12 Statistical Treatment 85
CHAPTER FOUR
4.0 RESULTS 87
4.1 Analysis of Tanning Extracts 87
4.2 Preparation of Different Vegetable Tannins Ratios 100
4.3 Assessment of the Leather Quality 103
4.4 Optimization of the Liming Process 118
4.5 Optimum Conditions for Liming 127
4.6 Preparation of Hide Powder 134
CHAPTER FIVE
5.0 DISCUSSION 137
CHAPTER SIX
6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS 158
6.1 Summary 158
6.2 Conclusion 160
6.3 Recommendations 162
REFERENCES 163
xii
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Raw hides and skins are converted to leather in a process called tanning
(Mahdi et al., 2009). Tanning chemically stabilizes hides and skins against bacterial
attack and convert the raw material into leather (Leticia et al., 2015). The
conventional use of tannins as agents for converting animal hides and skin to leather is
one manifestation of the most evident activity of the tannins, which is their ability to
interact with and precipitate proteins, including the proteins found in animal skin.
There are two types of Tanning: mineral (Chromium) and vegetable tannings.
Chromium is commonly used as mineral tanning agents (Commision, 2003).One of
the desirable qualities of chrome tanning over vegetable tanning is the high speed of
protein fixation leading to the high shrinkage temperature of the resultant leather and
an extra ordinary dyeing suitability.
Chrome tanning is the most widely used by the leather industry, because it
makes leathers with excellent physical and organoleptic properties. Approximately 90
% of the tanning process is carried out with chromium (III) salts. However, only a
fraction of chromium salts used in the tanning process (60%) reacts with the hides and
the skins. The rest of the salt (40%) remain in the tanning exhaust bath and are
subsequently sent to effluent treatment plant where the chromium salts end up in the
sludge (Mwinyihija et al., 2006). Leather wastes containing chromium are considered
hazardous waste and must be placed in special landfills(Marsal et al.,2012, as cited in
Spier et al., 2015).
On the other hand, vegetable tanning has always been one of the most
important alternatives to Chromium tanning as an environmental friendly system and
2
it is considered the “green tanning agent” becauseof its biodegradation (Jianzhonget
al.,2009,Spier et al., 2015). According to Faxing et al. (2005) and Bi (2006),
vegetable tanned leather has excellent fullness, mouldering properties, wear
resistance, air permeability and solidness; hence, properties as mentioned above
obtained from Chrome tanning may also be achieved by preparation and modification
of the vegetable tannins. Vegetable tanned leather is used in making heavy leather
such as furniture leather, garment leather and shoe upper leather. Worldwide,
researchers are paying particular attention to the use of vegetable tanning agents to
replace chrome tanning agent (Koloka and Moreki, 2011). Vegetable tanned leather is
the oldest and most classic type of leather, combining the values of quality and
tradition (Castiello et al., 2008). To safeguard and improve these traditional leathers,
Professor H.R. Procter, one of the pioneers in applying scientific principles to leather
manufacture, said, ―Science must follow before it can lead‖ (cited in Reed, 2013);
there is a need to study the process that local tanners use and analyse the tanning
strength of the vegetable tanning material they use (Nduru, 2015).
The principles of vegetable tanning have not changed since ancient times, still
using the tanning properties of plant materials, mainly extracted from trees like oak,
chestnut and mimosa, as well as quebracho and tara from Latin America. Previously,
the skins were hung to macerate in vats in direct contact with the bark, roots, berries
and leaves for lengthy periods of time (up to 18 months or even two years), but now,
concentrated extracts are used. These have optimal tanning capacity and have allowed
maceration times to be considerably reduced(Premier Vision Leather, 2017).
Vegetable tannins are polyphenolic secondary metabolites of higher plants,
and are either galloyl esters and their derivatives, in which galloyl moieties or their
derivatives are attached to a variety of polyol-, catechin- and triterpenoid cores
3
(gallotannins, ellagitannins and complex tannins), or they are oligomeric and
polymeric proanthocyanidins that can possess different interflavanyl coupling and
substitution patterns (condensed tannins) (Khanbabaee and Ree, 2001). Bate-Smith
(1962) as cited by (Hagerman, 2002) defines tannins as “water-soluble phenolic
compounds having molecular weights between 500 and 3000 giving the usual
phenolic reactions and having special properties such as the ability to precipitate
alkaloids, gelatin and other proteins”.
There are three (3) major types of vegetable tannins: hydrolysable, nonhydrolysable
(condensed) and complex tannins (Haroun et al., 2013). The
hydrolysable tannins are readily hydrolysed by acids, alkalis or enzymes (tannases)
into a sugar or a related polyhydric alcohol (polyol) and a phenolic carboxylic acid.
Depending on the nature of the phenolic carboxylic acid, hydrolysable tannins are
subdivided into gallotannins and ellagitannins. Hydrolysis of gallotannins yields gallic
acid while hydrolysis of ellagitannins yields hexahydroxydiphenic acid which is
isolated as ellagic acid. Hydrolysable tannins are considered as one of the most potent
antioxidants from plant sources (Haroun et al., 2013). However, large molecular
weights tannins limit penetration into the collagen fibres and lower the thermal
stability or tanning effect (Leticiaet al., 2015). Complex tannins are the combination
of both hydrolysable tannins and condensed tannins (Lokeswari and Bompalli, 2015).
The condensed tannins produce leathers with high shrinkage temperature of 70 to 80
oC. Whereas, hydrolysable produce leathers with shrinkage temperature of 70 to 74 oC
(Salminen et al., 2011).
Collagen molecules in skin is composed of three polypeptide chains with triple
helical structure, and they are summed up through hydrogen bonding to form collagen
fibres(Liao, 2003). In the tanning process, the collagen reacts with the tannins.
4
Although, the aromatic ring of vegetable tannins contains phenolic hydroxys, the
aromatic ring still keeps hydrophobicity. Studies have indicated that tannins first
approach the surface of collagen fibres by hydrophobic bonding, and then combine
with collagen fibres by multi-hydrogen bonding. Other components of plant extracts,
including polyphenolic compounds with small molecular weight, are not able to form
multi-hydrogen bonding with collagen fibres due to the limited phenolichydroxylsor
lack of structure of ortho-phenolic hydroxyls (Liao, 2003). For this reason, they have
relatively weaker adsorption capacity on collagen fibres. It is the distinctive molecular
structures of collagen fibres and tannins that establish the foundation of adsorption
selectivity of hide collagen fibres to tannins. Survey into the utilization of small
phenolic compounds (ranging from 500-3000Da) such as catechin is carried out to
improve penetration, sorptive capacity and binding ability with subsequent in situ
enzyme-catalysis and sulphitation.
Shrinkage temperature (hydrothermal stability) is one of the properties that is
routinely used to characterize collagen (Covington et al., 1997). Whether nature,
structurally modified or chemically modified, shrinkage temperature is the effect of
wet heat on the completeness of the material usually in terms of the denaturation
transition. The discerned initiation of the transition is referred to as the shrinkage
temperature reflecting the observation that collagenic materials respond to wet heat by
shrinkage. The main reaction between the vegetable tannins has always been thought
to be by hydrogen bonds formed between the hydroxyl groups on the polyphenols and
oxygen or nitrogen atoms on the protein (Teng et al., 2013; Covington et al., 1997). It
has however been found that polyphenols also fix to amino side chains by electrostatic
salt links with carboxylate or hydrogen bonding with carboxylic acid groups
depending on the pH (Teng et al., 2013).There is a positive correlation between the
5
molecular weight and the binding capacity, and the sorptive ability of tanning; that is,
the higher the molecular weight of the tannin, the stronger the tanning ability it will
present (Luizet al., 2002; SLTC, 1999).
Tannins are widely found in parts of plants such as bark, wood, fruit, leaves,
roots and growths. Tannins are found in the plant kingdom widely distributed such as
wattle, oak, chestnut, mangrove, quebracho, myrobalans, sumac, Turkish gall,
potentilla, Divi-Divi, locust bean, palmetto, hemlock, eucalypts, pomegranates,
gallnuts from oak and sumac which contains the highest occurring level of about 50 to
75 % tannins (gallotannins). There are so many areas in which tannins can be applied,
ranging from wine production to pharmaceutical applications. Phenolic metabolism in
plants is complex, and yields a wide array of compounds ranging from the familiar
flower pigments (anthocyanidin) to the complex phenolic of the plant cell wall
(lignin). However, the groups of phenolic compounds known as tannins are clearly
distinguished from other plant secondary phenolics in their chemical reactivities and
biological activities.
1.2 Statement of the Research Problem
In the quest to explore more sources of vegetable tanning materials, only a few
of the materials investigated are of economic importance. The Nigerian leather
industry has depended mainly on imported tannins of Mimosa and Quebracho and to a
lesser extent on the local plant Bagaruwa (Acacia nilotica). This indigenous plant has
not met the needs of the leather industry in Nigeria and the result is that the
importation of tannins stiffles the leather industry. Nigeria is blessed with vast
vegetation and biodiversity; the problem however, is that only limited studies have
been carried out on alternative sources of tannins. There is therefore the need to
6
reappraise this area of research to search for new and sustainable local sources of
vegetable tannins suited for the Nigerian leather industry and the world at large.
The Nigerian Institute of Leather and Science Technology (NILEST), Zaria
has screened about one hundred (100) vegetable tannin plants and found their
concentrations low except Parkia clappertoniana, Acacia nilotica and Caesalpinia
coriaria (Adewoye, 1986). Apart from the general problem of low hydrothermal
stability of the leather where vegetable tannins from Parkia clappertoniana are used,
there is also the unique problem of low penetration into the collagen fibre. About 40%
of Chromium used during tanning process remains in the waste and thedisposal of
chromium contaminated sludge produced as by-products of the waste water treatment
is becoming a widely known environmental problem in leather industry (Nduru, 2015;
Moorthy and Mekonnen, 2013).
Tannery effluent containing chrome adversely affects the mitotic processes
and lessens seed germination in extensively cultivated pulse crops. At high
concentrations chromium is toxic, mutagenic and teratogenic. Due to the above
mentioned disadvantages of chrome tanning, the tanners are now encouraged to adapt
new ecofriendly methods of tanning such as vegetable tanning materials (Moorthy and
Mekonnen, 2013 as cited in Nduru, 2015; Bielicila et al.,2005; Mole, 1993).
The combination tannages between mineral and vegetable tannins have been in
use to produce semi-chrome and chrome-retan leathers (ALCA, 1957, as cited by
Haron, et al., 2012). Since the character of leather is determined by the first tannage,
the synergy between two vegetable tannin is expected to give the leather the organic
character, thus making it more eco-friendly than the chrome-retan (Borasky et al.,
1949 as cited by Haron et al.,2012). There is need to further source for raw materials
for tanning without compromising the quality of the resultant leather (Teng et al.,
7
2013). Nigeria‘s leather industry is the second highest foreign
exchange earner after the oil industry, exporting over 600 million square feet of
leather in 2009, and earning about $680 million from tanned skin. The leather industry
offers a huge potential for growth, even though it constitutes mainly the small and
medium scale enterprises. Nigeria has one of the largest economies in sub-Sahara
Africa and the fifth fastest growing economy in the world, but it is heavily reliant on
oil and gas exports, which makes it very unstable because growth is dependent on
prevailing conditions in the global oil market. The Central Bank of Nigeria (2010)
reports that the heavy dependence on the oil sector is reflected by the fact that the nonoil
sector contributed only 6.5% of GDP. Hence, in order to develop a balanced
economy there is a clear need to expand the growth of the non-oil sector, one of which
is the leather industry. Export figures show that the leather industry was the strongest
non-oil export in 2005 with exports in excess of $160 million as reported by the
Nigerian export policy (Mohammed and Wuyah, 2014).
One of the leading sectors in Nigeria driving national output, employment and
export is agriculture sector. The agriculture sector of the economy, which currently
accounts for about 24 % of GDP, has been acclaimed to have the potential of
contributing about 65 per cent of employment generation and 50 per cent export share
if its vast and enormous value-adding opportunities in agroindustry are explored. The
livestock agro-industrial segment, especially the leather industry, presents an even
more compelling narrative of revenue generation and industrial deepening through
value and supply chain integration
(https://www.thisdaylive.com/index.php/2017/07/03/).
8
1.3 Significance of the Study
This research is expected to develop alternative sources of tannins which are
eco-friendly. Vegetable tanned leathers have the advantage of being biodegradable
and fitting well with consumer needs at both performance and appearance (Teng et al.,
2013). Development in vegetable tannin extract could lead to the production of more
versatile product base, like tannic acid, dyes and adhesive (Hemingway, 1992). The
national economy would be enhanced through the reduction in importation of tannins.
The cost of leather production and the effect of environmental pollution associated
with chrome tanning would be reduced (Nduru, 2015). In Nigeria, Caesalpinia
coriaria is not well known as tannin producing plant especially by the traditional
tanners and, therefore, has not been developed to be used. Therefore, the low
hydrothermal stability produced by the vegetable tannins can be overcome by
formulating the two classes of tannins (condensed and hydrolysable tannins) together,
to improve the quality of the resultant leather.The findings of this research will serve
as a means for the development of protocol of vegetable tanning using alternative
sources of tanning materials.
1.4 Aim and objectives
The aim of this research is to improve the leather quality produced by
optimizing liming, and increasing reactivity of tannins obtained from Caesalpinia
coriaria and Parkia clappertoniana. The aim would be achieved through the
following objectives:
i. extraction of tannins from Caesalpinia coriaria (DD)and Parkia
clappertoniana(PC);
9
ii. evaluation of the tanning strength of the vegetable tanning materials;
iii. modification of tannins using chemical and biological catalysis;
iv. characterization of the extracts before and after the modification;
v. preparation of different ratios of Caesalpinia coriaria with Parkia
clappertoniana;
vi. optimization of the liming process of the collagen;
vii. development of a protocol for commercial tanning of leathers using the
optimum conditions obtained;
viii. examining the quality of the tanned leather; and
ix. Preparation of hide powder.
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