Molecular weights and tanning properties of tannin fractions from the Acacia mangium bark

摘要

The bark of Acacia mangium was smashed and extracted by acetone solution, and the extract was then degreased by petroleum ether. The degreased solution was extracted by diethyl ether and ethyl acetate successively. In this way, the tannin of A. mangium was divided as diethyl ether fraction, ethyl acetate fraction, and water fraction, respectively. The molecular weight of these tannins was measured by gel permeation chromatography (GPC), and the particle sizes of tannin were examined by Zetasizer ZS instrument. The results showed that the ether fraction consisted of the smallest size molecule with average molecular weight of 415 Da, possessing weaker tanning ability but fast penetration rate. The molecular weight of ethyl acetate fraction was 1788 Da, and it showed a significant tanning ability. For the water fraction, the molecular weight was 2808 Da with better tanning ability, and the biggest particle size was shown in the tannin. The thermal stability of the hide powder and cowhide tanned by these tannins was as followed: Water fraction > ethyl acetate fraction > diethyl ether fraction; the penetration was: diethyl ether fraction > ethyl acetate fraction > water fraction. These results could provide a valuable reference for the use of the A. mangium tannin.