An Eco-Benign Semi-Metal Tanning System for Cleaner Leather Production

摘要

In this study we developed a semi-industrial- scale tanning process to replace chrome tanning in the production of high quality prosthetic leathers, based on a multi-step vegetable-aluminium tannage. Tara and mimosa tannins were used as vegetable tanning agents in order to obtain a wet-white tanned leather; a pretannage with glutaraldehyde or a preparation based on masked multi-functional phosphonium compound (THPS) were introduced to improve penetration of tannins. The treatment of pelt with THPS instead of chromium before vegetable-aluminium tanning allows it to reach a shrinkage temperature of up to 106 degrees C by using half as much tannin. The liquid wastes of the phosphonium compounds and the tanning vegetable-aluminium solution are capable of biodegradation to the level of some proteins, which is evidenced by the ratio BOD: COD. Besides, the absence of chromium compounds in the liquid waste improves the biodegradation of the other substances. It was determined that leather treatment with glutaraldehyde or phosphonium compounds positively influences the leather's ageing resistance. The leather tanned with tara tannins has more stable properties than the others assessed. The extra stability is likely to be due to mechanism of tanning process. Peculiarities of interaction between vegetable tannins and collagen were studied by IR-spectroscopy. The influence of pretreatment by different compounds before tanning on the thermal properties of derma collagen was studied by DTA and DSC.