FRACTIONAL ISOLATION AND PHYSICOCHEMICAL CHARACTERIZATION OF ALKALI-SOLUBLE LIGNINS FROM WHEAT-STRAW

Six alkali-soluble lignin fractions were sequentially extracted from p artially dewaxed wheat straw with sodium hydroxide at increasing stren gth from 0.25 to 2.00M, and the chemical compositions are reported. Th e physico-chemical properties of the lignin fractions were characteriz ed by nitrobenzene oxidation. and UV- IR-, and C-13-NMR spectroscopy. A new method of two step precipitation was proposed in this study to o btain lignin fractions relatively foe of polysaccharides. it was found that 60.8% wheat straw lignin was released during the above alkali tr eatments at 30 degrees C. The isolated lignin fraction contained very small amounts of polysaccharides, 1.4-1.7%, and had low molecular-aver age weights between 1200 and 1560. They are more condensed than the ty pical hardwood or softwood lignins.