Interaction of aluminum and hydrolysable tannin polyphenols: an approach to understanding the mechanism of aluminum vegetable combination tannage

Abstract

Semi-metal tanning systems have gained importance in recent times as an alternative for chrome tanning. Many reports are available regarding vegetable-aluminum combination tanning systems, but the mechanism of interaction between the aluminum and the vegetable tanning molecules has not been elucidated in detail. This study involves the determination of the complexing behavior of aluminum with the hydrolysable tannin, myrobalan and with the molecular species viz., gallic and tannic acid of hydrolysable tannin. Stoichiometry and binding constant of the polyphenolics-aluminum complex have been studied. It is observed that aluminum exhibits strong binding with hydrolysable tannin polyphenols. Externally prepared myrobalan-aluminum complex has been employed for the tanning studies, which showed a 10°C increase in shrinkage temperature compared to the self-tanning of the combination system.