THE EFFECTS OF ALKALINE LEACHING ON PULP BLEACHABILITY AND PHYSICAL-PROPERTIES

The effects of alkaline leaching on pulp bleachability. and physical properties were studied. Pulps with kappa numbers in the range of 16 to 48 were leached for 15 min at 100-degrees-C with 0.9 M NaOH. Delignification in alkaline leaching was between 17 and 30%. Successive delignification of unbleached kraft softwood pulp by alkaline leaching and oxygen delignification resulted in 25% more lignin removal than O2 delignification alone. Relative to normally washed pulp, leached pulp could be C(D)E-bleached to a lower kappa number with the same bleaching chemical charge; AOX production was proportional to the kappa number of either type of pulp. Leached pulp was slightly harder to beat, and had slightly higher tear and lower breaking length. Alkaline leaching can produce pulp with a lower kappa number for a given overall physical strength.