Structural Differences Between Commercial Acacia Mangium Tannin and Its Effluent

Abstract

Recycling and reuse techniques provide an efficient way to overcome the environmental issues of the chrome tanning effluent. However, only few vegetable tanning related recycling techniques were developed due to the limited information about the effluent. In this study, a common vegetable tanning process was performed with a commercial Acacia Mangium tannin (CAMT) to produce Acacia Mangium tanning effluent (AMTE). The tannins in the AMTE and CAMT were characterized using Fourier transform infrared, nuclear magnetic resonance spectroscopy, matrix assisted laser desorption/ ionization time of flight mass spectrometry, gel permeation chromatography and elemental analysis. The results showed that the stereochemistry and flavan-3-ol subunits of the tannins in the AMTE were the same with the CAMT. However the differences between the tannins in the AMTE and CAMT were presented in terms of the tannin category, molecular weight, and quantities of sulfo acid group. Tannins in the AMTE were mainly composed of procyanidin, while prodelphinidin and procyanidin content showed comparable in the CAMT. Average molecular weight of the AMTE was 1315Da, in contrast to an obviously higher value in the CAMT (2025Da). Meanwhile, higher sulfonic acid group content was also found in the AMTE. These differences were deduced in accordance with the collagen binding ability of the tannins. Results will be valuable for reuse and recycling of vegetable tanning effluent.