Structural Characterization of Lignin Isolated from Wheat-Straw during the Alkali Cooking Process

To investigate the behavior of lignin during the alkali cooking process with different alkali doses, this work demonstrated the structural characteristics illustrated by spectroscopic analyses. Gel permutation chromatography (GPC) and nuclear magnetic resonance (NMR) indicated that the lignin was composed of typical structures for a grass, generally with S and G units and small amounts of H units. The main substructures present were β-O-4 aryl ether linkages, and there were lower amounts of β-β and β-5 linkages. Alkali treatment conditions had evident effects on the chemical structures and properties of lignin. Moreover, NMR indicated that alkali cooking caused lignin to depolymerize more easily with increasing severity and to condense.