Water Absorptiveness of Handsheets Produced with Various pH Levels of Pulp Suspension, AKD Dosages and Mixing Times

Abstract

The objectives of this study were to determine the effects of high pH levels of pulp suspension and high dosages of alkyl ketene dimers (AKD) on the water absorptiveness of handsheets. Various mixing times were applied for the pulp suspension-AKD mixing conditions and analyzed for their effects. Handsheets were produced with various pH levels (pH 8, 9 and 10) of pulp suspension, AKD dosages (0.25, 0.50, 0.75 and 1.00% oven-dry weight (o.d.wt.) of pulp fiber) and mixing times (1, 5 and 10 min). The results indicated that the water absorptiveness of handsheets produced with 0.25% o.d.wt. of pulp fiber of AKD at any pH level of pulp suspension or prepared with any dosage of AKD in the pulp suspension at pH 8 was lower with a mixing time of 5 min, while that of handsheets produced with 0.50% to 1.00 % (o.d.wt. of pulp fiber) of AKD in the pulp suspension at pH 9 and 10 was higher with a mixing time of 5 min. This was possibly because the higher dosages of AKD could ensure sufficient AKD-oligomers were retained in the handsheets to promote good sizing, while the number of β-keto ester bonds established between the AKD and the surfaces of pulp fibers and fines was insufficient after a short mixing time of 1 min. Although some AKD could also be hydrolyzed with a long mixing time of 10 min, the excess amount of AKD could still react with the surfaces of pulp fibers and fines with β-keto ester bonds and the remaining AKD would also be retained in the handsheets as oligomers to promote good sizing. In addition, the stronger basic conditions would favor the formation of ester bonds.