Sustainable collagen composites from New Zealand sheepskin : from extraction to application : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering, Massey University, Palmerston North, Manawatu New Zealand

Abstract

Sheepskin, a low-value by-product of the New Zealand meat industry, is largely discarded despite its potential as a source of collagen. This thesis investigates the extraction, characterisation, and application of sheepskin collagen in sustainable fibre-based composites. Collagen was extracted using acid, acid-enzyme, and alkali methods, with pre-treatment and extraction parameters systematically evaluated to optimise yield and investigate its properties. Characterisation by FTIR, SDS-PAGE, SEM, and small-angle X-ray scattering confirmed preservation of fibrillar collagen under suboptimal and optimal conditions, while highlighting variability in molecular weight and purity across extraction methods.

Further investigation of the acid-enzyme extraction was conducted to establish the process variables determining the optimum yield and collagen content. The extracted collagen was applied as a coating on self-assembled cellulose fibre sheets, and performance was compared with gelatin coatings. Collagen improved surface wettability, barrier performance, tensile properties, and thermal behaviour, with effects dependent on coating concentration. Gelatin coatings provided some functional enhancements but were less effective at fibre network integration. Advanced synchrotron micro-computed tomography (micro-CT) revealed three-dimensional coating penetration, fibre-matrix interactions, and structural differences between collagen and gelatin composites, directly linking internal microstructure to observed macroscopic properties.

This work demonstrates that sheepskin, an underutilised agricultural by-product, can be transformed into functional collagen suitable for bio-based composites. The findings provide both a sustainable route for waste valorisation and foundational knowledge for developing collagen-based materials with tailored mechanical, barrier, and thermal properties. Future work should focus on scaling extraction processes, optimising coating integration, and extending micro-CT analysis to dynamic or environmental testing to further enhance the utility of sheepskin-derived collagen in sustainable materials applications.