P 100 TCF Bleaching of Softwood Kraft Pulps to High Brightness, 1994 Pulping Conference Proceedings

N.A. Troughton, F. Desprez, J. Devenyns

P100 sequences with alkaline hydrogen peroxide as the only bleaching chemical like Q P P* can be used to fully-bleach softwood Kraft pulps to 90 oISO brightness whilst retaining good physical properties. A prerequisite for efficient P100 bleaching is that the pulp is delignified as much as possible with extended cooking and oxygen delignification, but high brightnesses can also be achieved at high H2O2 charges for pulps with high kappa numbers. For example, brightening a kappa 27 softwood Kraft pulp to 90 oISO requires 7 %odp H2O2. If the incoming kappa number is reduced to 13.3 with oxygen prebleaching, 5 %odp H2O2 is required. With “super-extended cooked pulps” a single P* bleaching stage is all that is required for high final brightness. If the incoming kappa number is further reduced by extended delignification and oxygen prebleaching to kappa number 4, 3 %odp H2O2 is required to meet the same target.