STRUCTURAL CHARACTERIZATION OF BROWN-ROTTED LIGNIN

Naturally brown-rotted lignin was structurally characterized by various chemical and spectroscopic techniques. Our results of extensively decayed Douglas-fir indicate that modification of lignin by brown-rot fungi is mainly oxidative. In addition to modification of aromatic ring structures by demethylation, advanced decay by brown-rot fungi proceeds in the direction of partial depolymerization, perhaps involving aryl ether interunit bond cleavage, and oxidation and cleavage of the lignin side chain structures. Ring and side chain modification results in a significant increase in both phenolic and aliphatic hydroxyl and carboxyl groups, which makes this lignin chemically more reactive. Our results also suggest that aromatic hydroxylation is not involved in the softwood lignin modification by brown-rot fungi. In the course of this work various isolation procedures for fractionating the lignin into different molecular weight ranges were examined, and it was found that refluxing with hot NaOH is a simple method that may have potential industrial uses. © 1990, Walter de Gruyter. All rights reserved.