Fractionation and characterization of physicochemical and structural features of corn stalk hemicelluloses from yellow liquor of active oxygen cooking
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The hemicellulosic fractions were obtained by graded ethanol precipitation from the yellow liquor of active oxygen cooking. The chemical composition, structural features, and thermal stability were investigated by a combination of HPAEC, GPC, FT-IR spectra, NMR spectra and TG. Sugar analysis suggested that the xylose was primary sugar unit in the hemicellulosic fractions and the final residue contained high amounts of uronic acids. The GPC results showed that only 5.31% hemicelluloses in the liquor showed high molecular weight (24,824 g/mol), the remainder of the hemicellulosic fractions were significantly degraded during the cooking process and presented low molecular weight (2020-4574 g/mol). The corn stalk hemicellulosic fractions were composed of (1 -> 4)-beta-D-xylopyranosyl backbones, but the side chains attached to the xylopyranosyl units were diverse, depending on the precipitation process. In addition, hemicelluloses with infrequent side chains were more thermally stable and could be precipitated with a low concentration of ethanol. (C) 2012 Elsevier B.V. All rights reserved.