Comparative study of lignins from ultrasonic irradiated sugar-cane bagasse

After ultrasonic irradiation of sugar-cane bagasse (SCB) in distilled water at 55degreesC for 40 min and continuing stirring for 80 min, the irradiated SCB was sequentially treated with 0.5 M NaOH, 0.5%, 1.0%, 1.5%, 2.0% and 3.0% H2O2 at pH 11.5, and 2 M NaOH at 55degreesC for 2 h, which solubilized 3.3, 59.7, 15.5, 4.4, 5.5, 1.7, 0.6 and 0.6% of the original lignin, and 13.4, 38.2, 11.9, 4.5, 9.0, 2.4, 1.2, and 11.3 % of the original hemicelluloses, respectively. In total, the sequential extractions resulted in a release of 91.2% of the original lignin and 91.9% of the original hemicelluloses, which were higher than in the case of corresponding extractions without ultrasound pre-treatment. The eight lignin fractions were comparatively characterized by chemical composition, structural features, molecular weights, and thermal stability using alkaline nitrobenzene oxidation, acid hydrolysis, UV, FT-IR, H-1 and C-13 NMR spectroscopy, GPC, and thermal analysis. Compared to the lignins obtained without ultrasound, the lignin fractions prepared with the assistance of ultrasound had the same primary structure, composition, and similar or slightly higher purity. (C) 2004 Society of Chemical Industry.