Effects of pretreatment temperature and alkali concentration on the composition of alkali-soluble lignins from wheat straw

A new rapid method of two step precipitation for isolation of alkali-soluble lignins with relatively free of polysaccharides from wheat straw was proposed in this study. The isolated alkali-soluble lignin fractions LA contained rather low amounts of neutral sugars (0.7-1.0%) and had low average molecular weights (960-1440 Da). The isolated lignin fractions LA contained roughly equal amounts of guaiacyl (G) and syringyl (S) units with relatively fewer p-hydroxyphenyl (H) units, and appeared to be closely associated to phenolic acids and glucuronic acid or 4-O-methylglucuronic acid. The chemical compositions in each of the fractions are reported. The physico-chemical properties and structure features of these lignin fractions LA were characterized by UV-, IR-, C-13-NMR-spectroscopy, and alkaline nitrobenzene oxidation. (C) 1996 John Wiley & Sons, Inc.