Towards Sustainable Leather Production: Vegetable Tanning in Non-aqueous Medium

Abstract

The process of stabilizing the skin collagen against denaturation under heat, enzymes, stress etc. – popularly described as tanning is carried out either using metal ions (predominantly Cr(III)) or vegetable tannins derived from plant sources rich in polyphenols. Conventional leather processing is carried out in aqueous medium and hence the tannins have been extracted into water, sulfited to increase water solubility and then sold as spray dried extracts. Classical drawbacks include the low resistance of the extracts to bacteria and fungi, copious quantities of water required for extraction and tanning etc. In an attempt to make the leather processing sustainable, taking cue from other economically viable methods for tannin extraction, this paper looks at paradigm shift from water extraction of tannins to solvent based extraction, followed by leather processing in solvent. The results presented with ethanol as the green solvent highlights the significance of the developed method, in not onlyenhancing tannin to non-tannin ratio (T/NT), but also improving thermal stability of the tanned collagen at microscopic rat tail tendon (RTT) and macroscopic leather level.