Characterisation of degraded organosolv hemicelluloses from wheat straw

Treatment of the dewaxed wheat straw with acetic acid-H2O (65/35, v/v), acetic acid-H2O (80/20), acetic acid-H2O (90/10), formic acid-acetic acid-H2O (20/60/20), formic acid-acetic acid-H2O (30/60/10), methanol-H2O (60/40), and ethanol-H2O (60/40) using 0.1% HCl as a catalyst at 85 °C for 4 h degraded 42.4, 58.7, 70.0, 65.1, 76.5, 14.2, and 22.2% of the original hemicelluloses and 78.2, 80.0, 88.2, 89.4, 94.1, 23.5, and 37.4% of the original lignin, respectively. It was found that substantial hemicelluloses and lignin were degraded during the treatment with organic acids. The optimum condition for degradation of hemicelluloses was found to use a mixture of formic acid-acetic acid-H2O (30/60/10), which yielded 76.5% of the original hemicelluloses from wheat straw. Xylose was a major constituent in all the degraded hemicellulosic preparations. Glucose and arabinose appeared in noticeable amounts. Uronic acids, principally 4-O-methyl-d-glucuronic acid occurred in a small amount. Galactose, mannose, and rhamnose were present as minor components. In comparison, the five degraded hemicellulosic preparations isolated during the treatment with organic acids were more linear and partially acetylated, whereas the two acidic alcohol-degradable hemicelluloses were more branched. The FT-IR and liquid-state 13C NMR analyses revealed that the organosolv treatments under the acidic conditions substantially degraded the hemicellulosic polymers as shown by their lower molecular weights ranging between 8480 and 18,940 g mol−1. The thermal stability of the hemicellulosic preparations, degraded during the aqueous organic acids, was lower than that of the hemicellulosic preparations, degraded during the aqueous alcohols.