Efficient total halogen-free photochemical bleaching of kraft pulps using alkaline hydrogen peroxide

Total halogen-free bleaching of kraft pulps was conducted by an oxidative photochemical process at room temperature using alkaline hydrogen peroxide. Selection of an appropriate wavelength of light was crucial for effective bleaching and avoiding degradation of cellulose. The wavelength of the light has to be selected so that the light is absorbed only by the colored compounds in the pulps and not by the bleaching reagents or the pulp itself. When a long-wavelength black-light fluorescent lamp was used in combination with aqueous hydrogen peroxide solution at pH 11, the bleaching efficiency for hardwood and softwood kraft pulps reached the same level as that obtained by conventional two-stage elemental chlorine-free processes.