NMR Analysis of Oxidative Alkaline Extraction Stage Lignins

Summary Chlorine dioxide delignified pulp was subjected to various oxidative alkaline extraction stages (EAr, E, EO, EP, and EPO) from which the residual and effluent lignins were isolated and characterized by 1H and 13C NMR. Results of the NMR analyses indicate an increase in unconjugated carboxyl content of the lignins with the alkali treatment; a decrease in phenolic and formyl groups with oxidant reinforcement, especially oxygen; and an enrichment in aromatic methoxyl groups with increasing amount of oxidant reinforcement. The alkaline extracted pulps were further treated to a second chlorine dioxide stage from which the residual lignins were extracted and analyzed by 1H NMR. Significant structural differences were noted between the various oxidative E stage and D1 stage lignins.