No description available.

No description available.

Thesis--Hamburg. / Lebenslauf. "Literatur-verzeichnis": p. iii-v.

Inaug.-diss.--Leipzig. / Lebenslauf. "Literaturverzeichnis": p. [5]-11.

Inaug.-diss.--Basel. / Curriculum vitae. "Literaturverzeichnis": p. 171-175. "Zeitschriften und jahresbarichte": p. 176.

Thesis (Ph. D. (Chemistry))--Rhodes University, 2006.

This thesis reports on research undertaken to investigate the implementation of a Circular approach within the leather industry, through the definition of a framework and development of an economic decision-making support tool. The core objective of the research is to identify the underpinning opportunities and challenges involved in creating recycling solutions for leather waste. The research contributions can be considered in four key areas. The first part of the thesis consists of a review of the use of leather across industry sectors and the existing waste management and recycling systems for leather waste. On consideration of this review it clearly shows a lack of systematic thinking around the creation and optimisation of recovery systems for leather waste. This review concludes that there is significant room for improvement of the current waste management and recycling solutions for leather waste. A variety of value-added products can be recovered from these wastes but only if the leather can be successfully separated from the other materials (such as rubbers and polymers) within end-of-life products and manufacturing wastes. The second part of the research defines a framework for implementing a Circular approach within the leather industry. This framework supports mapping and characterisation of the leather waste stream and the design of recycling and processing strategies for leather waste. The third part of the research is concerned with the development of a decision-support tool for the economic viability of leather recycling systems. The support tool considers all cost factors and combines them to give a single factor upon which the economic effectiveness of different leather recycling scenarios can be evaluated. Finally, the validity of the framework for leather waste recycling is assessed through the completion of two case studies. These case studies demonstrate the flexibility of the framework in supporting both horizontal (across lifecycle) leather recycling and vertical (across industry sector) leather recycling. In summary, the research clearly highlights the need for systematic thinking and flexible strategies when creating leather recycling systems. Failure to incorporate flexibility into future recycling systems puts the recycling industries at risk of being unable to effectively manage future waste streams. Conversely, early consideration and incorporation of flexible processing strategies into recycling systems could enable the recovery of high-quality recycled materials that support a circular approach to manufacturing and resource use.

No description available.

Various oxygen- and nitrogen-donor ligands were investigated as potential zirconium masking agents in zirconium tanning. α-Hydroxycarboxylic acid ligands were identified as effective zirconium(IV) chelators in acidic aqueous solution. Glycolic acid, lactic acid, mandelic acid, 4-hydroxymandelic acid, 4-chloromandelic acid and 4-bromomandelic acid complexes were synthesised, isolated and characterised using a range of analytical techniques. Linear Free Energy Relationships were examined to optimise the stability of the zirconium complexes. Hammett [sigma] plots and Yukawa-Tsuno modified σ plots of the mandelate ligand and zirconium complex series indicated that inductive effects dominate within the benzene ring, however, mesomeric effects are significant outside the ring. Zirconium 4-hydroxymandelate complex solutions were identified as the most effective tanning agents and achieved shrinkage temperatures of 80 and 97ºC for hide powder and goatskin, respectively. The zirconium and 4-hydroxymandelic acid interact synergistically to yield leather equivalent to combination tanned leather in one step. Tanning was performed similarly to vegetable tanning processes with a pickle pH of approximately 5 and fixation was achieved upon acidification. Pilot-scale tanning of goatskin produced white tanned leathers and crust leathers which were physically and aesthetically comparable to matched chromium tanned material.

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