Chemical Aspects of Hydrogen Peroxide Bleaching. Part II the Bleaching of Kraft Pulps

Abstract

Kraft pulps contain a considerable amount of transition metal ions. It is demonstrated that unless these ions are thouroughly removed, alkaline hydrogen peroxide is an inefficient bleaching agent for kraft pulps due to a rapid decomposition into oxygen. If, on the other hand, the metal ions are removed from the pulp prior to bleaching under carefully selected conditions, alkaline hydrogen peroxide can be used to increase considerably the brightness of kraft pulps without seriously affecting the pulp viscosity. The results are interpreted with emphasis on the organic and inorganic chemical reactions of hydrogen peroxide. It is also suggested that the bleaching effect is a result of a simultaneous degradation and dissolution of lignin starting with phenolic lignin units.