Comparative study of hemicelluloses from rice straw by alkali and hydrogen peroxide treatments

First extraction of the dewaxed rice straw with 1% NaOH at 55°C for 2 h and then following treatment with 0.0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0% hydrogen peroxide at 45°C for 12 h at pH 11.5 solubilized 67.2, 77.2, 78.7, 83.7, 85.5, 87.3 and 88.5% of the original hemicelluloses, and 2.5, 9.8, 11.8, 12.1, 15.6, 16.4 and 17.8% of the original cellulose, respectively. Meanwhile, the two-stage treatment together resulted in a dissolution of 68.3, 85.4, 89.4, 92.7, 92.7, 94.3 and 95.1% of the original lignin under the conditions given, respectively. Comparison of these hemicellulosic preparations indicated that alkali treatment in the absence of H2O2 favoured solubilization of the small molecular size of hemicelluloses, which are rich in glucose, probably originating from α-glucan, while the second stage treatment by alkaline peroxide enhanced dissolution of larger molecular size hemicelluloses, which are rich in xylose, principally resulting from l-arabino-(4-O-methyl-d-glucurono)-d-xylan. The treatment by alkaline peroxide under the conditions used did not affect the overall structure of macromolecular hemicelluloses except for a noticeable degradation of cellulose and hemicelluloses during the treatment with more than 1.0% H2O2.