Zeolites as sustainable alternatives to traditional tanning chemistries

Abstract

Collagen-based composite materials are extensively studied and used in different fields, including tissue engineering, food applications and leather manufacture. Leather is the largest application of collagen where typical tanning chemistries include metal salts, polyphenolics and aldehydes. A new type of material that is gaining industrial significance is based on a composite of collagen and zeolite in the area of sustainable leather manufacture. This approach utilises simple, abundant, and benign chemistry, which provides leather with the physical properties needed for a range of possible applications. However, the stabilising interactions between collagen and zeolite are not yet known and would benefit from deeper understanding of the interactions and the impact on environmental parameters. The composite material reported here is made by treating animal hide collagen with zeolite using established processing technologies, commonly used in leather tanning processes, without the need for further specialised apparatus. The interaction between collagen and zeolite has been characterised by small-angle X-ray scattering (SAXS), infrared spectroscopy (IR), solid-state nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM) and zeta potential. SAXS shows unique changes in the scattering profile revealing zeolite and collagen interactions, which relate to a combination of covalent and electrostatic mechanisms. The zeolite forms a 3D network structure covering collagen fibres, improving protein stability against hydrothermal denaturation and creating material strength. The environmental and industrial impact has been evaluated based on reaction uptake, waste stream assessment and biodegradability. Zeolite tanning shows a positive influence on reaction uptakes, similar to industry best practice, waste water impact and positive biodegradability results. Through the deeper understanding of the van der Waals interactions between collagen and zeolite, and the positive environmental assessment, this work demonstrates the merits of this new stabilisation approach with the possibility of further expansion into other applications.