The aim of this study was to investigate the hemicelluloses extracted from Populus tomentosa Carr. by the hydrothermal method with ethanol. The influence of ethanol concentration on the hemicellulosic fractions was systematically studied. The chemical compositions and structural features of the hemicellulosic fractions were investigated by a combination of sugar analysis, gel-permeation chromatography, Fourier transform infrared spectroscopy, and one-dimensional proton and carbon-13 nuclear magnetic resonance, and two-dimensional heteronuclear single quantum coherence spectroscopy. Neutral sugar analysis of the hemicellulosic fractions revealed that a higher ethanol concentration (45%~80%) favored the isolation of hemicelluloses with more side chains and lower glucose contents. The molecular weights of these polysaccharides ranged between 2842 g/mol and 5101 g/mol. The results of this study indicate that the hydrothermal ethanol process provides a new pretreatment strategy for the isolation and extraction of biomass.

The purpose of this study was to explore the differences of the hemicelluloses extracted by hydrothermal pretreatment using water and alkaline solutions(Na OH or KOH). The physicochemical properties and structural characteristics of two water-soluble and four alkali-soluble hemicelluloses extracted from the triploid of Populus tomentosa Carr. through the hydrothermal pretreatment were comparatively studied. It was observed that the alkalis(Na OH and KOH) were more effective than distilled water as extractants. Sugar analysis showed that xylose(66.83%~86.49%) was the major constituent, followed by glucose(6.83%~18.49%). Mannose(1.40%~8.42%), galactose(2.17%~4.05%), and arabinose(0.21%~2.26%) were also detected in the hemicellulosic fractions. The results of gelpermeation chromatography(GPC) indicated that the hemicelluloses extracted using the alkaline solutions had relatively higher molecular weights than those solubilized in distilled water. Further, based on spectroscopic ¹Hnuclear magnetic resonance(¹H-NMR) and two-dimensional heteronuclear singular quantum correlation(2D-HSQC) analyses, it was confirmed that the hemicellulosic fractions had a major structure of(1→4)-β-D-xylan and a minor structure of(1→4)-α-D-glucan with small amounts of substituted sugars and glucuronic acid attached.