A study on AKD-size retention, reaction and sizing efficiency Part 1: The effects of pulp bleaching on AKD-sizing

摘要

The effects of pulp bleaching on alkyl ketene dimer (AKD) size retention, reaction and sizing efficiency were investigated using C-14 labelled AKD. The AKD-sizing efficiency, using laboratory hand sheets made from differently bleached (ECF/TCF) softwood and hardwood pulps were investigated. All pulps used were fines and extractives free in order to isolate the effect of fibre surface charge density on sizing. The results show that the retention of AKD increases with the surface charge density of the pulps in the absence of a retention aid, but that the effect of surface charge density is of less significance when using a retention aid (C-PAM) to retain the AKD. The AKD-size can be efficiently retained (70-90% retention), at similar retention aid additions, irrespective of the differences in surface charge density between the pulps. The results also showed that hardwood pulps were less reactive than softwood pulps. Extensive extraction procedures excluded the possibility that surface-active substances interfered with the sizing procedure. It is concluded that the major differences in the sizeability between certain commercial ECF/TCF bleached kraft pulps is most likely due to their contents of extractives and dissolved substances, as have been indicated in earlier reports, and not due to differences in surface charge density between the pulps.