Effects of ECF and TCF bleaching sequences on the properties of softwood kraft pulp

The effects of ECF, TCFz and TCFPaa bleaching sequences on delignification and pulp properties were studied using an oxygen-delignified softwood kraft pulp from a Finnish mill. Part of the pulp was submitted to a second oxygen stage before bleaching with elemental chlorine-free (ECF) and totally chlorine-free (TCF) chemicals including ozone (Z) and peroxyacetic acid (Paa). Routine and special analytical methods were used to evaluate the bleaching processes stage by stage. These methods include determination of residual lignin, carbohydrates dissolved, carbonyl groups formed in the pulp, viscosity after borohydride reduction and papermaking properties after PFI beating. The results are used to assess the technical and economic aspects of using ECF and TCF bleaching chemicals.