NMR analysis of oxidative alkaline extraction stage lignins

Chlorine dioxide delignified pulp was subjected to various oxidative alkali ne extraction stages (EAr, E, EO, EP, and EPO) from which the residual and effluent lignins were isolated and characterized by H-1 and C-13 NMR. Resul ts of the NMR analyses indicate an increase in unconjugated carboxyl conten t of the lignins with the alkali treatment; a decrease in phenolic and form yl 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 di oxide stage from which the residual lignins were extracted and analyzed by H-1 NMR. Significant structural differences were noted between the various oxidative E stage and D-1 stage lignins.