A guide to high-efficiency chromium (III)-collagen cross-linking: Synchrotron SAXS and DSC study

The inefficiency of the chromium (III)-collagen cross-linking reaction during conventional leather processing results in severe environmental pollution from the waste chromium in the effluent. A mechanistic study using synchrotron-based small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) on ThruBlu tanned leather, revealed the effect of chromium sulphate and its pre-treatments on collagen structure and stability. By pre-treating with complexing agents such as sodium formate and disodium phthalate, as well as nanoclay (sodium montmorillonite), the uniformity through bovine hide collagen matrix were improved significantly. These pre-treatments effectively reduce the reactivity of chromium during its cross-linking reaction with collagen while retaining its bound water. However, collagen pre-treated with a covalent cross-linker (glutaraldehyde) results in a decrease in both chromium-collagen cross-linking and bound water while improving uniformity. These molecular-level insights can be developed into metrics to guide us towards a more sustainable future for the leather industry.