BLEACHING OF SULFITE PULPS WITH PEROXO SA LTS

Various peroxo salts were evaluated as possible bleaching agents for p aper grade pulps. For economical as well as for ecological reasons the bleaching agents should be recyclable, possibly by electrolysis. Amon g the eligible candidates peroxidisulphates, peroxocarbonates and pero xoborates, only the latter ones proved to be useful. Sodium and potass ium peroxoborates were compared with hydrogen peroxide with regard to delignification and bleaching efficiency. Especially the potassium sal t showed to be least aggressive towards the pulp fibers. Thus the mech anical strength properties of pulps bleached by peroxoborates are bett er than comparable ones bleached by hydrogen peroxide. However the per oxoborate bleaching reaction proceeds more slowly because in this case the proper bleaching action is preceded by the formation of hydrogen peroxide. By increasing the reaction temperature the necessary reactio n times can be reduced without any abatement of fiber properties.