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

Fundamental elements of chrome-collagen interactions and the crosslinking mechanism at the molecular level have been investigated to gain detailed understanding that can be translated into improvements in the commercial process. Amide group hydrolysis during conventional liming proceeds by two mechanisms: direct hydrolysis with hydroxyl catalysis or intramolecular catalysed hydrolysis that can be measured by the degree of racemisation at L- asparagine. Gas chromatography mass spectrometry analysis of limed collagen demonstrated that there was no initial rise in the amount of D-aspartic acid during the first 24 hours of liming, indicating that, within the conventional period of liming, collagen remained intact. Circular dichroism has demonstrated that beamhouse processing has dispersive and relaxing effects on the collagen triple helices, but without disruption. Attenuated total reflection Fourier transform infrared spectroscopy analysis provided information regarding changes in the secondary structure of collagen during tanning. Complete breakdown of chrome tanned collagen was achieved by the use of a cocktail of proteolytic enzymes: this allowed an analysis of the isolated crosslinks, which indicated preferred reaction at aspartate sidechain carboxyls. This is supported by chrome tanning studies following treatment of collagen by amidase enzymes. Geometric details of chromium(lll) species involved in the tanning reaction were elucidated by extended X-ray absorption fine structure analysis. Linear tetrameric chromium species were found to be predominant in the tanning process. Direct measurements of the mechanism were made using electron spin resonance spectroscopy. A two-stage reaction mechanism is postulated: physical interaction and chemical complexation, affected by reaction conditions such as pH, temperature and the presence of neutral salts. Nuclear magnetic relaxation dispersion measurements confirmed changes in the speciation of chromium(lll) under tanning conditions.

The optimum cutting of various parts of a shoe, prior to shoe manufacture requires knowledge of the topographical variation of what are termed “lines of tightness”. Currently the cutting operation for shoe parts is guided by a general assumption about the pattern of the lines of tightness. There is a need to have available a system which can determine, in a non-destructive way, the lines of tightness in an indvidual piece of leather. Initially an image analysis system was developed to investigate the uni-axial deformation behaviour of leather. This technique provided more information about the stress-strain behaviour of a leather sample along the gauge length than a conventional mechanical test and it was possible to accurately measure the strain distribution along the gauge length. A system was developed which could determine the relative displacement of marked spots along the gauge length of the sample using images captured during a uni-axial, bi-axial or multi-axial tensile test. The separation of the marked spots along the direction of applied stroke allowed the determination of longitudinal strain while contraction across the width was also measured in some cases, which was useful in calculating the Poisson’s ratio of leather for which a great variation was observed between different locations (Butt, Belly, Neck etc). Various approaches were investigated to determine the lines of tightness. Firstly, the local Poisson’s ratio was observed since a higher value of this parameter was associated with these lines of tightness. Secondly, biaxial stretching of leather by a series of actuators for each axis indicated the lines of tightness along the actuator with lower strain values. Thirdly, the strain was measured when the leather was stretched along number of known axes. This latter technique appeared to be the best approach and mathematical modeling was investigated to provide further refinement. A mechatronics-based device by industrial application of the third approach was also proposed. The software was written using a graphical programming system (LabVJ EW)

A novel powder coating binder system based on UV-curable, semi-crystalline polyurethane acrylates has been developed for heat-sensitive and highly flexible substrates, such as leather. The developed powder coating film had good abrasion and adhesion properties. The concepts applied in this work were based on the adjustment and control of the degree of crystallinity of hinders by three ways: (i) formulating different molecular weight monomers for random copolymerization, (ii) introducing functional monomer with pendant groups and (iii) cross-linking during curing. Amongst the three approaches explored in this work, a combination of branching and cross-linking was found most successful. A crystalline binder with cross-linkable pendant groups was employed as the powder coating main binder; this is the major difference from other work on powder coatings where amorphous resin alone or partially blended with a crystalline component are used as binders. The preparation of UV curable powder coating binder resins and their properties, such as crystallinity, viscosity and tensile modulus and elongation to break have been studied by DSC, SEM, FTIR-ATR and DMTA methods. It was found that the polyurethane acrylate binders (made from DHBA, BEP, DEG and HDI etc.) are potentially useful for formulating novel powder coatings. The properties of the developed powder coating finished leather have been tested. Hot plating processes and an EMB application method for leather finishing have been discussed as well. Nano-scale silica particles surface modified with acrylate has been studied, and their properties or properties of powder coatings formulated with the particles have been characterized. The powder coating rub fastness was improved by formulation with surface modified nano-scale silica particles

Leather is a widely used material whose handling character is still assessed manually by experienced people in the leather industry. The aim of this study was to provide a new approach to such characterisation by developing Artificial Neural Network models to investigate the relationship between the subjective assessment of leather handle and its measureable physical characteristics. Two collections of commercial leather samples provided by TFL and PITTARDS were studied in this project. While the handle of the TFL collection covered a varied range, the PITTARDS collection was all relatively soft leather and with less difference within the collection. Descriptive Sensory Analysis was used to identify and quantify the subjective assessment of leather handle. A panel constituted of leather experts was organised and trained to: 1) define attributes describing leather handle; 2) assess specific leather handle by responding to questionnaires seeking information about the above attributes. According to the analysis of the raw data and the assessment observation, the attributes that should be used for training the artificial network models were "stiff", "empty", "smooth", "firm", "high density" and "elastic". Various physical measurements relating to leather handle were carried out as follows: standard leather thickness, apparent density, thickness with 1 gram load and 2 gram load, resistance to compression, resistance to stretching, surface friction, modified vertical loop deformation, drooping angle and BLC softness. The parameters from each measurement were all scaled on range 0 to 1 before being fed into network models. Artificial neural networks were developed through learning from the TFL examples and then tested on the PITTARDS collection. In the training stage, parameters from physical measurements and attribute gradings provided by descriptive sensory analysis were fed into the networks as input and desired output respectively. In the testing stage, physical measurement parameters were input to the trained network and the output of the network, which was the prediction of the leather handle, was compared with the gradings given by the panel. The testing results showed that the neural network models developed were able to judge the handle of a newly presented leather as well as an expert. Statistical methods were explored in the development of artificial neural network models. Principal Component Analysis was used to classify the attributes of leather handle and demonstrated that the predominant and most representative attributes out of the six attributes were "stiff", "empty" and "smooth". A network model called physical2panel, predicting the above three attributes from three physical parameters was built up by adopting a novel pruning method termed "Double-Threshold" which was used to decide the irrelevance of an input to a model. This pruning method was based on Bayesian methodology and implemented by comparing the overall connection weight of each input to each output with the limitation of two thresholds. The pruning results revealed that among the sixteen physical parameters, only three of them, - the reading from BLC softness guage, the compression secant modulus and the leather thickness measured under 1 gram load were important to the model. Another network model, termed panel2panel, that predicts the other three attributes "firm", "high density" and "elastic" from the prediction of the model physical2panel was developed and also proved to work as well as a leather expert panel. The conception of a 3D handle space was explored and shown to be a powerful means of demonstrating the findings.

No description available.

Hides and skins used as a raw material for leather manufacture may be contaminated with various microbial species including potential pathogens. Many bacterial species such as Bacillus, Staphylococcus, Micrococcus and Pseudomonas were isolated from raw hides/skins, and hides/skins at different stages of leather making process. The extreme environmental conditions present during a conventional tanning process due to hazardous chemicals may prevent the growth of bacteria present on hides/skins. On the other hand, partial or total replacement of the hazardous chemicals with non-hazardous chemicals, during a best available technologies (BAT) process, may provide suitable conditions for microbial growth in tannery effluent and hides/skins. Therefore, the aim of the project was to determine the survival and growth of the various bacterial species during the conventional and BAT leather-making processes. The beamhouse and tanning stages were studied, as the majority of the environmental pollution occurs during the early stages of the leather making process. Both the pre-soaking and soaking stages during the conventional and BAT leather-making processes provided suitable conditions for bacterial (Bacillus cereus, Pseudomonas aeruginosa and Staphylococcus spp.) growth and proliferation. The results showed a significant reduction in the number of B. cereus found during the conventional and BAT unhairing processes. Limited B. cereus growth was observed during the subsequent reliming process. Bacillus cereus growth also occurred during the deliming and bating processes (conventional and BAT), followed by a decrease during the conventional and BAT pickling processes. No B. cereus colonies were isolated during the chrome tanning process. Growth of P. aeruginosa was inhibited during both the unhairing and reliming stages of the conventional and BAT leather making processes. A reappearance and recovery of P. aeruginosa in the subsequent deliming and bating (conventional and BAT) processes, indicated that deliming and bating processes may provide suitable growth conditions for P. aeruginosa. On the other hand, both the conventional and BAT pickling processes, and the chrome tanning processes hindered P. aeruginosa growth. Staphylococcus spp. were present throughout the conventional and BAT leather-making processes. A large reduction in the number of Staphylococcus spp. was observed during the unhairing and reliming processes (conventional and BAT). Growth of Staphylococcus spp. occurred during the subsequent deliming, bating, pickling and chrome tanning stages for both the conventional and BAT leather-making processes. The biochemical assays for bacterial identification confirmed the presence of B. cereus, P. aeruginosa and Staphylococcus spp. during the leather processing. The pulsed-field gel electrophoresis (PFGE) method of DNA fingerprinting confirmed that the bacterial species isolated during the leather manufacturing processes were the inoculated B. cereus and P. aeruginosa, and no alteration of the DNA of above-mentioned bacteria occurred during the processing. Overall, the research showed that bacterial species are capable of surviving during both the conventional and BAT leather-manufacturing processes. The bacterial species prefer the environmental conditions during the pre-soaking and soaking processes, while the unhairing and reliming processes did not favour the growth of bacterial species. Bacterial colonies were enumerated during the deliming and bating processes indicating that the unhairing and reliming processes did not cause total destruction of the bacterial cells. Alternatively pickling and chrome tanning processes were found to have suppressed the growth of bacterial colonies.

Vegetable tannins used in tanning of hides and skins are limited to surface reactions by their large molecular weights. The molecular weight reduces penetration into the skin and lowers the thermal stability or tanning effect. Investigation into the utilisation of small phenolic compounds such as catechin to improve penetration with subsequent in situ enzymecatalysed polymerisation may provide a novel and alternative tanning agent. In this research, catechin was oxidised by enzymatic catalysis using laccase, with the polymerisation confirmed by FT-IR and UHPLC. Tanning experiments were undertaken to measure the effect of laccase-catalysed polymerisation of catechin in the thermal stabilisation of collagen, by monitoring the change in shrinkage temperature between the treated and untreated sample of hide powder (ΔTs). This study demonstrates that the stabilisation of collagen (ΔTs) is increased with the use of in situ enzyme-catalysed polymerisation. Depolymerisation of condensed tannins is presented as an alternative source of low molecular weight phenolics to be applied in the stabilisation of collagen. In this research, mimosa tannin from the Black Wattle tree (Acacia mearnsii) was used in the depolymerisation process. Preliminary experiments on depolymerisation were undertaken using the methods laccase-mediator system and L-cysteine in mild acidic medium, both showing unsatisfactory results. Acid-catalysed depolymerisation followed by nucleophile addition is a common analytical method for determining the degree of polymerisation of proanthocyanidins. The acid-catalysed depolymerisation method was scaled-up, with the addition of pyrogallol as a nucleophile trapping agent, and powdered depolymerised mimosa was obtained. Data show an increase in the monomeric content and decrease in percentage of condensed tannins for the acid-catalysed process, indicating the potential of the depolymerisation of mimosa tannin in obtaining environmentally friendly sources of low molecular weight phenolic compounds for use in large scale/industrial applications. The depolymerised product was applied in the stabilisation of hide powder and goat skin. Using hide powder, data show that the laccase-assisted polymerisation of the depolymerised mimosa reached higher values of ΔTs in comparison with the conventional process employing unmodified mimosa. Using goat skin, the new process achieved similar values of ΔTs as the conventional process. In order to obtain similar results for goat skin as obtained with hide powder, an optimisation may be carried out. Therefore, data obtained demonstrates the potential of the new route in vegetable tanning of leather.

Waste management in the leather industry worldwide is an issue of major importance for both solid and liquid wastes. It has been recognised that there are major environmental impacts from the poorly managed disposal of such wastes and these have a clear health impact upon human society. Within Europe, under EU driven legislation, the costs of wastes management are increasing rapidly and there is a clear need to research improved methods to cost effectively deal with leather industry wastes. Biodegradation (anaerobic), as a management option, of solid wastes from the leather industry is an area that is attracting increased interest in recent years as being a technique that has wide public acceptability as well as process efficiency. However, tanning agents that prolong the lifetime of leather goods have a negative impact on biodegradation and this needs to be addressed before efficient treatment can occur. To drive the agenda this research has the aims of • Highlighting the effects of tanning agent on anaerobic digestion. • Understanding the mechanism(s) by which different leather tannages can biodegraded. • Developing a process to reverse the action of tannage. Leather solid wastes were anaerobically digested using Serum Bottle Assays (SBA). The effect of a range of vegetable, mineral and aldehyde tanning agents of leather on the rate of anaerobic digestion was assessed. Common tanning agents used included; myrica, valonea, glutaraldehyde and chrome. To further identify key factors for cost effective anaerobic digestion, tanned hide powders and tanned leathers were also pre-treated using autoclaving, liming, enzymes etc, in an attempt to determine whether tannage may be reversed. Major techniques used in the research include: anaerobic digestion, Biochemical Methane Potential (BMP), Total Solids contents (TS), Gas Chromatography (GC) and Gas Chromatography Mass Spectrometry (GC-MS). Hydrolysable tannins are less resistant to anaerobic digestion than condensed tannins. However, enzymatic pre-treatment reduces the resistance and this offers a new effective pre-treatment route. Thermal pre-treatment also decreased resistance to anaerobic digression especially for chrome, glutaraldehyde, myrica and tannic acid tanned leathers. Chemical pre-treatment also generally lowered the resistance to anaerobic digestion. Selective pre-treatment offers a means of improving the cost effectiveness of anaerobic digestion of leather and therefore enabling a new waste management method to be adopted by the industry. A relationship emerges, in some cases, between chemical structure of tanning agent and inhibition of anaerobic digestion. This offers the possibility of producing new, designed organic tanning agents with, suitable properties, to be adopted by the industiy, The research agenda within the leather industry is still ongoing and recommendations for future research are addressed