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-s oluble lignins with relatively free of polysaccharides from wheat stra w was proposed in this study. The isolated alkali-soluble lignin fract ions LA contained rather low amounts of neutral sugars (0.7-1.0%) and had low average molecular weights (960-1440 Da). The isolated lignin f ractions LA contained roughly equal amounts of guaiacyl (G) and syring yl (S) units with relatively fewer p-hydroxyphenyl (H) units, and appe ared to be closely associated to phenolic acids and glucuronic acid or 4-O-methylglucuronic acid. The chemical compositions in each of the f ractions are reported. The physico-chemical properties and structure f eatures of these lignin fractions LA were characterized by UV-, IR-, C -13-NMR-spectroscopy, and alkaline nitrobenzene oxidation. (C) 1996 Jo hn Wiley & Sons, Inc.