Acetylation of wheat straw hemicelluloses in N,N-dimethylacetamide/LiCl solvent system

Hemicellulose acetates were prepared under homogeneous reaction conditions in the system N,N-dimethylacetamide/lithium chloride by reacting the native hemicelluloses with acetic anhydride in the presence of 4-dimethylaminopyr idine within 72 h at 60-85 degrees C. The products obtained were characteri sed by means of Fourier transform infrared chromatography, gel permeation c hromatography, and thermal analysis. The degree of substitution of acetylat ed hemicelluloses ranged between 0.74 and 1.49 as a function of experimenta l conditions. Under an optimum reaction condition (85 degrees C, 60 h), ove r 80% hydroxyl groups in native hemicelluloses were acetylated. The molecul ar weight measurements showed that a significant degradation and hydrolysis of the products appeared at only a prolonging period of 72 h. It was found that the thermal stability of the products increased by esterification. (C ) 1999 Elsevier Science B.V. All rights reserved.