Physicochemical characterisation of residual hemicelluloses isolated with cyanamide-activated hydrogen peroxide from organosolv pre-treated wheat straw

Seven residual hemicellulosic preparations (19.6–45.0% of the original hemicelluloses) were extracted from wheat straw pre-treated with various organic solvents using 1.8% H2O2–0.18% cyanamide at 50 °C and pH 10.0 for 4 h. Their chemical compositions and physicochemical properties were determined using GC, HPLC, GPC, FT-IR and 13NMR spectroscopy. The results indicated that all the residual hemicellulosic preparations were heteropolysaccharides containing xylose, glucose, arabinose, galactose, mannose, rhamnose and 4-O-methyl-α-d-glucopyranosyluronic acid. The predominant monosaccharide was xylose, ranging between 67.7% and 81.9% of the total neutral sugars, composed mainly of l-arabino-(4-O-methyl-d-glucurono)-d-xylan. The content of contaminant lignin in the isolated residual hemicelluloses was 2.89–5.31%. The Mw values of the two residual hemicellulosic preparations H6 and H7 (42,710 and 44,080 g mol−1, respectively) obtained from the aqueous-alcohol pre-treated straw were much higher than those of H1–H5 (12,980–15,950 g mol−1) extracted from the organic acid pre-treated straw.