Effects of Bleaching Parameters on the Brightening of Pulps, 1996 International Pulp Bleaching Conference Proceedings

A new evaluation method for the determination of bleaching performance was developed, and the general model derived by application of dimensional analysis was tested in a simplified form suitable for presentation as a diagram. Peroxide bleaching results obtained with various mechanical pulps were tested, e.g. groundwood (GW), thermomechanical pulp (TMP) and chemithermomechanical pulp (CTMP). All pulps used were produced from softwood in pulp mills. It was demonstrated that a diagram of this type can be used in evaluation of the bleaching results. Both brightening or darkening (indicated by the relative reciprocal reflectance) and chemical utilisation (indicated by the relative residual concentration or charge) are simultaneously considered in the diagram. The alkali charge in peroxide bleaching was demonstrated to be very critical in mechanical pulp bleaching. Successively increased alkali charge was found to improve the brightening until a certain critical point of alkali charge was attained. After this first perfect bleaching phase a non-brightening phase followed, although consuming considerable amounts of peroxide. This resulted from increased alkali which evidently began to decompose the peroxide.