Physicochemical characterization of lignins from rice straw by hydrogen peroxide treatment

Extraction of the dewaxed rice straw with 1% NaOH at 55 degreesC for 2 h an d following treatment without and with 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% hy drogen peroxide (H2O2) at 45 degreesC for 12 h at pH 11.5 resulted in a dis solution of 68.3, 85.4, 89.4, 92.3, 92.3, 94.3, and 95.1% of the original l ignin, respectively. Meanwhile, the two-stage treatment together solubilize d 67.2, 77.2, 78.7, 83.7, 85.5, 87.3, and 88.5% of the original hemicellulo ses and degraded 2.5, 9.8, 11.8, 12.1, 15.6, 16.4, and 17.8% of the origina l cellulose under the conditions given, respectively. Analyses of these lig nins revealed that alkali-soluble lignin fractions did not suffer sever oxi dation, but nearly 60% of the original lignin was dissolved out during the first stage of alkali treatment. In the second stage of alkaline peroxide t reatment, the residual lignins were substantially released and enriched in oxidized carbonyl and carboxyl groups. In comparison, the isolated eight pu re lignin samples were further characterized by both destructive methods su ch as alkaline nitrobenzene oxidation and nondestructive techniques such as ultraviolet (UV), Fourier transform infrared (FTIR), and carbon-is magneti c resonance spectroscopy (C-13-NMR) as well as gel permeation chromatograph y (GPC), and the results are reported. (C) 2000 John Wiley & Sons, Inc.