Effect of Gallic Acid Content on Tannin-Titanium (III) Combination Tanning

The combination tanning using titanium (III) and hydrolysable tannin extracts was reported as a better tannage to improve the properties of leather than condensed ones. One of the most obvious differences between these tannin extracts was the gallic acid content. To clarify the effect of this reactive structure on tannin-Ti (III) combination tanning, Acacia Mangium tannin extract (no gallic acid), Orange Oil tannin extract (25% gallic acid) and Strawberry Tree tannin extract (40% gallic acid) were selected for tannin-Ti (III) complex and tanning experiments. The quantity of precipitation, pH of complexation system and shrinkage temperature were used as main evaluation factors of this investigation. Under different temperature and pH conditions with different dosages of tannin extracts and Ti (III) agent, their complex ability and tanning ability were studied respectively. The results show that: the gallic acid in tannin extracts could improve its complex ability with Ti (III) under different temperature and pH conditions; the tannin extracts with more gallic acid showed higher effective complexation index, and better reactivity to complex with Ti (III). So, higher thermal stability was obtained with less tanning agent; under tanning condition, the more the gallic acid content in tannin extracts, the higher the thermal stability of leather presented. This research could provide a reference for the Ti (III) - vegetable extracts combination tanning.