Organosolv- and alkali-soluble hemicelluloses degraded from Tamarix austromongolica: Characterization of physicochemical, structural features and thermal stability

Three organosolv- and three alkali-soluble hemicellulosic polymers were degraded from dewaxed Tamarix austromongolica (TA) with DMSO, 70% ethanol containing 2% triethylamine (TEA), 70% ethanol containing 0.5% NaOH at 70 °C for 5 h, and 1 M KOH, 1 M NaOH and 1 M NH3·H2O at 50 °C for 5 h, respectively. Comparative studies showed that more linear hemicelluloses were easy to obtain in NaOH and KOH aqueous solution, which have larger molecular weights (M¯w, 24,100-28,500 g mol−1), and contained mainly xylose (72.5-73.6%) and uronic acids (11.1-11.4%). The thermal degradation behaviour showed that significant degradation in the range from 190 to 390 °C, and more branched polymer was more easily degraded at low temperatures. FT-IR and 2D HSQC spectra showed that the major chemical structure of the KOH-soluble hemicelluloses consists of a linear backbone of (1 → 4)-β-d-xylopyranosyl residues, and at least one of the xylose residue is monosubstituted at O-2 by a 4-O-methylglucuronic acid, and l-arabinose attached to O-3 of the xylose residues, giving a typical ratio of arabinose/4-O-methyl-α-d-GlcpA/xylose is estimated to be 1:4:23.