Sugarcane bagasse hemicelluloses were partially acetvlated with acetic anhydride using N-bromosuccinimide (NBS) as a catalyst under mild conditions in an almost solvent-free system. The overall yield and degree of substitution (DS) were varied from 66.2 and 83.5% and between 0.27 and 1.15, respectively, by changing the reaction temperature and duration. It was found that the yield and DS increased with reaction temperature from 18 to 80degreesC and reaction time between 0.5 and 5.0 h. The results showed that treatment of the native hemicelluloses with acetic anhydride using NBS as a catalyst conveniently provided the corresponding biopolymer esters. The products were characterized by FTIR, C-13-NMR spectroscopy, and thermal analysis. The new biopolymer acetates were thermally stable to over 200degreesC but underwent significant and rapid thermal degradation when heated above the onset of thermal degradation. (C) 2004 Wiley Periodicals, Inc.