Effect of extraction procedure on the molecular weight of wheat straw lignins

Wheat straw was treated with sodium hydroxide at Various conditions, or ball-milled for 4, 8, 16, and 144 h in a porcelain rotary ball-mill and sequentially hydrolyzed by a cellulase for 3 days, and it was delignified by ethanol/water mixture (60:40, v/v) with 0.02 N H2SO4 as a catalyst at 75 degrees C for 1, 1.5, 2, 2.5, 3, 5 and 12 h, respectively. The alkali lignin fractions (LA) were isolated by two step precipitation. Milled lignins (LM) and enzyme lignins (LE) were extracted from the residues by 90% dioxane. Organosolv lignins (LO) were obtained by a traditional acidification method. The molecular weights of wheat straw lignins were determined by gel permeation chromatography (GPC). The effects of the extraction procedure on lignin molecular weight were examined in this study. The four lignin preparations showed low molecular-average weight (M-w 1400-2020). Alkali lignins LA, which were relatively free of associated polysaccharides, appeared to offer the greatest potential for structural characterization of straw and grass lignins. (C) 1997 Elsevier Science B.V.