EFFECT OF EXTRACTION PROCEDURE ON THE MOLECULAR-WEIGHT OF WHEAT-STRAWLIGNINS

Wheat straw was treated with sodium hydroxide at Various conditions, o r 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 deli gnified by ethanol/water mixture (60:40, v/v) with 0.02 N H2SO4 as a c atalyst at 75 degrees C for 1, 1.5, 2, 2.5, 3, 5 and 12 h, respectivel y. The alkali lignin fractions (LA) were isolated by two step precipit ation. 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 st raw lignins were determined by gel permeation chromatography (GPC). Th e effects of the extraction procedure on lignin molecular weight were examined in this study. The four lignin preparations showed low molecu lar-average weight (M-w 1400-2020). Alkali lignins LA, which were rela tively free of associated polysaccharides, appeared to offer the great est potential for structural characterization of straw and grass ligni ns. (C) 1997 Elsevier Science B.V.