Extraction and comparative characterization of ball-milled lignin (LM), enzyme lignin (LE) and alkali lignin (LA) from wheat straw

Ball-milled straw lignin LM and enzyme lignin LE were extracted with 95% dioxane, following with 50% (v/v) dioxane-water from ball-milled, for 1, 2, 4, 6, 8, 10 and 15 days wheat straw in a porcelain rotary ball-mill, and from the following hydrolyzed by a cellulase for 3 days straw residues, respectively. Alkali lignin LA was obtained by treatment of wheat straw with 0.5 M NaOH at 75 degrees for 2 h, and isolated by two steps of precipitation. The effect of ball-milling time (BMT) on lignin yield and molecular weight was examined in this study. Optimal BMT was 6 days. A comparative study of the three lignin preparations, LM, LE and LA, using UV-, GPC-, IR-, C-13-NMR-spectroscopy and nitrobenzene oxidation, is reported. Alkali lignin LA, which is relatively free of polysaccharides and appeared to have high molecular weight, was found to be the greatest potential for further investigation.