Isolation and Fractionation of Hemicelluloses from Salix Psammophila

Waterand alkali-soluble hemicelluloses were isolated with hot water and 10% KOH at 25 °C from dewaxed and delignified Salix psammophila, respectively. The alkali-soluble hemicelluloses were then successively subfractionated by neutralization and subjected to gradual precipitation in the end, using ethanol concentrations of 15, 30, 45, 60, 75 and 90%, respectively. Chemical composition, physico-chemical properties and structures of the 8 precipitated hemicellulosic fractions obtained were established by sugar analysis, molecular weight determination, FT-IR, H, C and 2D HSQC NMR. It was found out that the water-soluble hemicelluloses were more branched, having a low molecular weight (6060 g mol), whereas the alkali-soluble hemicelluloses were less branched, having higher molecular weights (17110-85540 g mol), with xylose and uronic acid as the main sugar components. In addition, the less branched hemicelluloses with large molecules were precipitated in lower ethanol percentages while, with increasing ethanol concentration, more branched hemicelluloses with low molecular weights were obtained. That is why, linear hemicelluloses could be recovered at lower ethanol concentrations, and more branched hemicelluloses could be obtained at higher ethanol concentrations. According to FT-IR, H, C and 2D HSQC NMR studies, the alkali-soluble hemicelluloses had a main structure composed of a (1→4)-linked β-D-xylopyranosyl backbone with 4-O-methyl-α-D-glucuronic acid attached to the O-2 of the xylose residues.