RAPID ISOLATION AND STRUCTURAL CHARACTERIZATION OF ALKALI-SOLUBLE LIGNINS DURING ALKALINE TREATMENT AND ATMOSPHERIC REFINING OF WHEAT-STRAW

The chemical compositions of two alkali-soluble wheat straw fractions LA, isolated by two steps of precipitation from two different alkali-r efining treatment regimes are reported. The physico-chemical propertie s of the two lignin samples were characterized by using gel permeation chromatography (GPC), ultraviolet (UV), infrared (IR) and nuclear mag netic resonance (NMR) spectroscopy and alkaline nitrobenzene oxidation . No significant difference of the phenolic monomers composition was f ound in the case of the two lignin samples. The isolated lignins conta in rather low amounts of polysaccharide sugars (0.7%) and have low mol ecular weights (M(w), 1906-1937). The results also showed that two lig nin fractions LA (alkali lignin), contained roughly equal amounts of g uaiacyl (G) and syringyl (S) units with relatively fewer p-hydroxyphen yl (H) units and appeared to be very closely associated to phenolic ac ids and glucuronic acid or 4-O-methylglucuronic acid.