Animal hide processing : impact on collagen structure

摘要

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.