The manufacture of parchment and leather from animal skin involves processes that remove hair, fats, and other macromolecules. Although it is well understood that the collagen fibres "open up" during processing, the study in this thesis used small and wide- angle X-ray diffraction to measure quantitatively the changes induced at the nanoscopic and microscopic levels. Collagen axial rise per residue is unaffected by salting, liming and drying of animal hide. The intermolecular lateral packing distance between the hydrated collagen molecules (1.4 nm) increases after salting (1.5 nm) and liming (1.55 nm) drying causes a reduction to 1.2 nm in all samples. The axial D-period is reduced by 1 nm after liming and is unaffected by drying. The average fibril diameter increased from 103.2 nm to 114.5 nm following liming, and the fibril-to-fibril distance increased from 122.6 to 136.1 nm. Furthermore, the effects of the solvents propan-2-one and 2-ethoxy ethanol on collagen structure were investigated. The D-period of the treated collagen was reduced by approximately 3 nm. Wide angle X-ray diffraction displayed clear peaks brought about by the presence of calcite, residual from the liming process. The presence of calcium carbonate was confirmed by Fourier transform Infrared spectroscopy. It was shown to differentiate between caprine and ovine samples, and the flesh and grain layers of the hide. Principal components analysis inferred from the differences in the calcite peaks that calcium carbonate uptake varies between animal species in the liming process. The solvent treatments did not appear to affect the Fourier transform infrared spectra. Efforts were made to investigate a treatment process of a fibrous collagen material for the leather industry that produces minimum effluents. Bovine collagen treated with tanning agents at chromium concentrations of (1, 3, 5, 7, 9, 11%), resulted in changes in the molecular packing within the collagen fibrils.

Thin grain leathers were taken from bovine sides and composites formed by saturation. Leather and composites were characterized by mechanical tests. They deform mostly by fibre extension, decrimping, translation and rupture. The relative proportion of each is strain dependant and the restricting forces determine the tensile stress response. In unstrained leather, frictional forces or polar bonds, predominate, whilst in composites, polymer bonds prevail. Aqueous impregnants probably form additional polar bonds. The stress response of leather is largely strain rate insensitive but composites have a composition dependant, strain rate sensitivity and a higher stress relaxation rate. It is doubtful whether any bonds remain intact beyond 12% strain where leather and composites exhibit an increase in Poisson!s ratio, a change in stress relaxation behaviour and, in leathers, an ill-defined stress yield point which probably marks the end of the fibre decrimping in retan leather. Below 12%, strain, full chrome leather has a high modulus and retan a lower one. Composites also have high moduli but in those of aqueous polymers, the yield point is sharper and occurs at 5%, strain along with a maximum stress relaxation rate and, with one polymer, an increase in Poisson!s ratio. Beyond 12% strain, frictional forces or entanglements cause progressive fibre rupture, beginning at 15%, strain in full chrome leather, at 30% in retan, and increasing exponentially in both up to rupture at 40% strain. No polymer brought forward the onset of fibre rupture, most delay it. All polymers further restrict fibre movement at the highest strain rates employed but at lower rates soft polymers can act as lubricants with increasing polymer content and composite failure strain increases while secondary modulus decreases. A simple additive model describes composite stress relaxation. Tensile stress prediction requires a complex network model which does not account for the effect of polymer content.

The influence of drying leather at 30% strain on the tensile strength and crack resistance of the grain layer of chromium tanned bovine leather was examined. The effect of drying under different strains was also examined. Bovine wet blue splits were stretched (by 30%) either along one axis (uniaxial) or two perpendicular axes (biaxial) and dried in this stretched condition. The strength and the fracture toughness of the resulting crust leather, was then evaluated. Drying leather under 30% uniaxial strain resulted in an increase in the tensile strength for samples cut along the stretch axis. However the variation of tensile strength with angle of cutting the specimen with respect to the stretch axis can be described by the Tsai-Hill theory that is applicable to fibre composite materials. The essential work of fracture approach was applied for the first time to leather specimens cut both longitudinally and transversally to the stretch axis. For all the samples examined, a strong anisotropy in the fracture behaviour was observed. The fracture resistance for cracks propagating along the stretch direction in uniaxial samples was lower than in the transverse direction, this fracture anisotropy being enhanced at higher applied strains. Drying under uniaxial strains above 15%, resulted in an increase in the fracture toughness for cracks running transversally to the strain direction, but at the same time, it seriously reduced the fracture resistance for cracks propagating along the strain direction resulting in global yielding, a phenomenon that rendered the evaluation of fracture resistance by use of essential work of fracture approach unattainable. Drying under biaxial strains above 15% seriously reduced the fracture resistance of leather both perpendicular to and parallel to the backbone. The application of optical microscopy to observe the propagation of cracks through the grain layer led to the conclusion that drying under biaxial strain can cause a reduction in crack resistance due to changes in the size and nature of a highly orientated fibrous zone close to the crack tip. X-ray diffraction studies were made in order to relate the fracture behaviour to leather structure. The X-ray data was correlated with experimental data in order to investigate the influence of pre-stretching on the strength and hence quality of leather during manufacture and their relationship to the fibrous collagen microstructure.

One of the major problems facing the meat and leather industries is dung cladding on hides. Dung dried onto hides is difficult to remove during the early stages of processing, resulting in the necessity for prolonging the soaking step, with the consequence of risking bacterial damage to the hides. Microscopic examination of dung on hide reveals that adhesion is between the dung and the hair alone, with no sticking of the dung to the epidermis. This accounts for the difficulty in removing dry dung; the matrix of the hair within the dung creates a strong composite material. Analysis shows that major components of the composition of dung are lignocellulosic materials (lignin, hemicellulose and cellulose). This project concerns solubilising the dung faster, to reduce soaking time by targeting these components with enzyme technology, using hemicellulases, cellulases, and laccases from commercial products and a range of fungal organisms (Coriolus versicolor and Aspergillus niger). Removal of dung from hide pieces is affected by the action of cellulase, xylanase and laccase separately over 20-24 hours. Mixture of these enzymes removes dung in 6-8 hours demonstrating that synergistic activity is more effective than separate enzyme treatments. When commercial enzyme mixture or Coriolus versicolor or Aspergillus niger cultural broths were used to effect dung removal in tannery drums in a larger scale experiment, in some cases the removal of dung was observed within 1 hour by the help of the mechanical action and nonionic surfactant. The enzyme treatment did not affect the components of hide, such as collagen, hyaluronic acid and dermatan sulphate and it was found that enzyme treated leathers and control samples showed no differences in terms of their physical characteristics. Investigations in the mechanism of dung removal by spectrophotometry, chromatography and chemical techniques show that the enzyme treatments remove the dung from hides without changing the fundamental structure of the substrate. The enzymes probably attack the structural parts in lignocellulose, which are most susceptible to solubilising with enzymes: these attacks make small changes in the carbohydrate and lignin contents, but these changes are powerful enough for effective dung removal

A review across the periodic table of tanning effects of simple inorganic compounds reveals that many elements are capable of being used to make leather. But, if the practical criteria of effectiveness, availability, toxicity and cost are applied, the useflul options reduce to chromium (III) the benchmark orto titanium (IV) zucomum (V) iron (II/III) and aluminium (II) For mainly environmental reasons, alternative tanning agents to chromium are needed, However. none so far investigated match the all round properties achieved with chromium (III) salts. In tanning terms, the chemistry of titanium (IV) is dominated by the titanyl ion, TiO2, limiting its reactivity with collagen. An alternative approach to titanium tanning, using metastable titanium (III) salts as possible tanning agents, was investigated in this study. A method to determine the titanium content in leathers was developed. Complexes of Ti (III) were investigated using various spectroscopic techniques, including uv/vis spectroscopy, electron spin resonance, electron nuclear double resonance and nuclear magnetic resonance dispersion spectroscopies. The complexes used in subsequent tanning studies were based on titanium (III) citrate, gluconate and tartrate. However, in comparative trials with chromium (III) salts, the study highlighted that titanium (III) salts were not suitable for tanning collagen. Titanium (III) saks were found to be useflul in the production of semi- metal tamlages. The research was extended to investigate the hydrothermal shrinking of tanned collagen. Techniques such as extended x-ray absorption — fine structure and x-ray absorption near structure were used to investigate the interaction of chromium (III) tanning salts and titanium (III) complexes with collagen. The research demonstrated that the shrinking reaction is independent of the tannage. It involves instead the breaking of hydrogen bonds, rather than the breakdown of the tannin-collagen molecule. From this work, and a reappraisal of older work on the shrinking reaction, a new theory of tanning has been formulated based on co-operating units and the role of crystallinity in stabilising the collagen structure. The influence of the solvent is also discussed

Necin bark (1zadirach1a indica) contains a mixture of complex chemical components identified as: One procyanidin trirner Four dimers Cl Epicatechin-[4a-8j-epicatechin epicatechin. B1 Epicatechin- [4[3-8]-catechin, B2 Epicatechin- [43-8]-epicatechin, B3 Catechin-[4ct-81-catechin, B4 Catechin-[4a-81-epicatechin. Four well known monomers (+)-Catechin, (-)-Epicatechin, (+)-Gallocatechin, (-)-Epigallocatechin. Other compounds Quercetin, Kaempferol, Fisetin and Gallic acid These compounds were characterised by chromatographic and spectroscopic techniques, including by thiolytic degradation with toluene-a-thiol and using acetylated and methyl derivatives. Structural elucidation of the cleavage products was by ‘H-NMR. The backbone of the isolated compounds consisted mainly of a mixture of flavan-3-ol units with 2R- configuration. The purity of monomers, dimers and trimer was checked by HPLC on Lichrosorb RP8 column. The molecular weight distribution ranges between 250 and 5500 and the average molecular weight distribution was found to be 1550 by gel permeation chromatography. Gas chromatography-mass spectroscopy demonstrated the complex nature of NBT molecular masses consist of monomeric, dimeric and trimeric units of procyanidin B and C types respectively. IR and FT-IR spectroscopy results were consistent with the rest of the techniques used. The hydrothermal stability of neem bark tannin tanned and crosslinked hide powder and leathers was found to be paralleled to mimosa tannin extract. Studies of the physical properties of tanned and retanned leathers showed corn pai.ahility of micem bark tannins with mimosa tannin extract

The aim of this research was to understand better the rheological behaviour of part processed leather in order to improve area yield. Rheological behaviour was characterised in uniaxial tests by measuring the stress-strain relationship, the immediate and recovered set and stress relaxation. The influence of moisture content, time under strain and applied strain were determined. The effect of drying under strain was also explored. Results were interpreted using rheological and structural models. It was found that for wet leather the relationship between applied strain and long term set is nonlinear. Moreover, below a critical strain no set is imparted. At this critical strain there is a change from a bending to a tensile mode of fibre deformation. Long term set only occurs in wet leather when collagen fibres are subject to tension. In wet leather, recovery occurs because collagen fibres return to their initial bent configuration. The long term set of partially processed leather at low strains increases with decreasing moisture content because collagen fibres permanently deform due to the rupture of intra-fibre adhesions. Inter-fibre adhesions formed on drying result in a yield point on the stress-strain curve. At the yield point the adhesions rupture and the mode of fibre deformation changes from stretching between adhesions to bending. A model, which views the structure of leather as adhesion nodes, joined by segments of fibres, has been used to predict increases in the initial modulus caused by drying under strain, in terms of the recruitment of straight fibre segments between nodes. When material is held under strain, there is a proportionate decrease in stress and increase in the immediate set, which is shown to be consistent with the Maxwell model. The two stage recovery of set is fitted to a multiple Voigt model. A novel way of achieving area yield without loss of tensile strength or softness is suggested in which the leather’s structure is relaxed whilst remaining wet and is then fixed by drying rapidly under strain

Chrome tanned bovine leather comprises two principal strata, the grain and the corium. The tensile strength and specific work of fracture of these two materials was investigated using uniaxial tensile tests and trouser tear tests respectively. Corium material was observed to be intrinsically stronger and tougher than grain material. The greater resistance of corium material to fracture is attributed to the processes of fibre debonding and pull out. The viscoelastic nature of grain and corium material was investigated by examining differences in strength and toughness over a range of deformation rates. The ultimate tensile properties and the specific work of fracture of both grain and corium material are rate dependent. Energy dissipation during a strain cycle was measured over a range of strain rates and strain levels to determine the bulk hysteresis of grain and corium specimens. The influences of specimen orientation and fatliquor (oil) on strength and toughness are also considered. The notch sensitivity of grain and corium materials has been scrutinised. Corium material is highly notch insensitive, whereas the fracture of grain material is notably sensitive to the presence of notches. The mechanism of fibre orientation and the phenomenon of fibre independence (or fibre autonomy) are responsible for the notch insensitive fracture behaviour of corium material. Strain distribution was measured in grain and corium single edge notch specimens. The radius of curvature of the notch was assessed throughout deformation / fracture and local strains at two dimensional levels were measured. Local strains ahead of the advancing crack and the radius of curvature of the crack are considerably higher with corium specimens than with grain specimens

This study investigated the modification of leather rupture properties following impregnation with polyurethane. It was hypothesised that a better polymer - leather interaction would increase strength. Surface properties of leather fibres were altered (using a hydrophobic agent based on a phosphate ester) to more closely match those of the polymer. This resulted in a more even distribution of polymer on the leather fibrils. Application of the hydrophobic agent alone was investigated and optimum offers of the treatments determined. An untreated sample and one impregnated without surface treatment were included as controls. Trouser tear testing was used to assess rupture resistance as well as a stratigraphic tear test which was used to evaluate any changes in peeling properties. An approximately linear relationship between peeling strength and sample split depth was observed which indicated that the grain - corium junction is a gradually changing interface. The surface modification of fibres led to increases in tear strength. Applying polymer to leather with surface modified fibres resulted in further increases in tear strength. Investigation of single fibres determined that no treatments influenced the fibre strength. There was, however, a decrease in the interfacial bond strength between fibre and polymer when surface modification was used. This was related to an increased fibre pull out length for treated samples. Leathers of 11% hydrophobing agent and 10% polyurethane gave the best combination of tear strength and softness. It was concluded that polymer impregnation of hydrophobic leather resulted in a bonded fibre structure. When stress is applied to such leather, fibres debond from the network and disentangle from the fibre structure. Work must be done to overcome surface friction between fibre and polymer. However, there is a balance between (a) interfacial bond strength and friction, and (b) fibre strength. This balance can be manipulated to obtain optimum overall strengthening

The effects of ultrasound (38 kHz, 1.3 W cm2) on the dyeing, fatliquoring and tanning of leather have been investigated and the mechanisms whereby ultrasound influences these processes were elucidated. Compared with a conventional process, ultrasonic dyeing can either shorten the dyeing time by 40-70% or facilitate low temperature dyeing. This remarkable enhancing effect has been attributed mainly to an increased diffusion coefficient (D) of dyestuff in the presence of ultrasound. It was found that sonication is more effective in the initial phases than in the late phases of the dyeing process. Application of ultrasound during the fatliquoring process or simply in the preparation of fatliquors resulted in an increase of leather fat contents (up to 40%), especially in the inner corium layer, indicating an improved penetration. This can be partly attributed to a reduction of particle size by 20-30%. In contrast to dyeing, ultrasound was found to be more effective later rather than earlier in the fatliquoring process. Chromium and aldehyde tanning processes were accelerated only marginally (1 0%) but the mimosa tanning process was speeded up significantly (by up to 100%) by using ultrasound. Leathers tanned in the presence of ultrasound had shrinkage temperatures 3-5°C higher than conventionally processed controls. A more even chromium distribution and less chromium leaching were obtained after using ultrasound. The results showed that ultrasound can increase the dispersion rate and the available tannin content (by 7%) of mimosa, as well as reducing its particle size by 50%. It was also found that ultrasonic treatment can prevent mould from growing on mimosa tanned leathers. It is concluded that ultrasound is more effective in a process which involves a colloidal rather than a true solution system. The prevailing effects of ultrasound on the former processes are to increase the diffusion coefficient and reduce the aggregation. This is due to cavitation