Stearoylation of hemicelluloses from wheat straw

Stearoylated hemicelluloses with degrees of substitution 0.20-1.71 were pre pared by a rapid reaction of wheat straw hemicelluloses with stearoyl chlor ide using 4-dimethylaminopyridine as catalyst and triethylamine as acid acc eptor in a homogeneous N,N-dimethylformamide and lithium chloride system. U nder optimum conditions approximately 92% of the free hydroxyl groups in na tive hemicelluloses were stearoylated in 30 min at 75 degrees C. Molecular weight measurements showed only minimal degradation (less than or equal to 8%) of hemicellulosic chains during the rapid reactions at 75 degrees C for 10-35 min, while a noticeable degradation (similar to 20%) of the stearoyl ated hemicelluloses was observed during the reaction at 85 degrees C. Diffe rential thermal analysis studies revealed an increase of the thermal stabil ity of the stearoylated hemicelluloses. (C) 2000 Elsevier Science Ltd. All rights reserved.