The dependency of carbohydrate degradation on the oxidation of lignin during ECF bleaching is reviewed based on the results mainly obtained in Wood Chemistry Laboratory. The University of Tokyo.
The progress of lignin oxidation during oxygen bleaching can be separated into three clearly distinguished phases. Oxidation of the first phase is mainly due to the direct reaction of molecular oxygen with phenolic unit in lignin. During the second and third phases, oxidation of lignin occurred mainly due to the active oxygen species. Those active oxygen species are also present in the first phase but probably reduced by the reaction with phenolic groups in lignin. However, those active oxygen species could attack carbohydrates as well as lignin. Since the active oxygen species are produced by the reaction of oxygen with lignin. the oxidation of carbohydrates during oxygen bleaching process can be regarded as “co-oxidation” phenomena. The effect of metal ion on the formation of those active oxygen species and the reaction selectivity of active oxygen species to react with lignin and carbohydrates were studied by various model experiments. The formation of active oxygen species and the effect of metal ion, and. cooxidation of carbohydrate and lignin during ozone bleaching are also briefly discussed.