Formation of Hydroxyl Radicals from Hydrogen Peroxide and their Effect on Bleaching of Mechanical Pulps

Abstract

Abstract The formation of hydroxyl radicals from hydrogen peroxide in alkaline solutions and under the conditions of hydrogen peroxide bleaching of pulps was investigated. The results lend support to the generally accepted view that the decomposition of alkaline hydrogen peroxide is catalyzed by redox processes involving transition metal ion species. The formation of hydroxyl radicals by one-electron reduction of hydrogen peroxide in this process is believed to be catalyzed primarily by mononuclear transition metal ion complexes, polynuclear species being far less efficient in this respect. It was found that a certain formation of hydroxyl radicals during alkaline hydrogen peroxide bleaching of pulp may have a beneficial effect on the final brightness. This finding is ascribed to the cleavage of crosslinks in the rigid lignin matrix which facilitates penetration of the bleaching reagent(s). Silicate does not appreciably suppress the formation of hydroxyl radicals in alkaline hydrogen peroxide solution. Th...