Structural Characterization of Residual Lignins Isolated with Tetraacetylethylenediamine-Activated Peroxide from Ultrasonically Irradiated Organosolv Pretreated Wheat Straw

摘要

Residual lignin (14.5-30.8% of the original wheat straw lignin) was obtained by post-treatment with 2% H{sub}2O{sub}2-0.2% tetraacetylethylenediamine (TAED) at pH 11.8 for 12 h at 48℃ from ultrasonic irradiation (0-35 min) following by organosolv treatment of wheat straw. Analyses of the released residual lig-nins revealed that TAED-activated peroxide post-treatment led to side-chain oxidation of the lignin as shown by a slight increase of aliphatic carboxyl groups. The eight residual lignin preparations were relatively free of bound polysac-charides, indicating substantial cleavage of the α-ether linkages between lignin and polysaccharides. The lignin preparation solubilized during the TAED-activated peroxide post-treatment had a higher molecular weight and thermal stability than that of the corresponding lignin fraction released during the alkaline organosolv pretreatment with or without ultrasonic assistance. Detailed structural characterization of the residual lignin was performed by 13{sup left}C NMR.