Effect of relative humidity and unreacted AKD on AKD sizing

The role of relative humidity and unreacted AKD molecules on the sizing development of AKD (alkylketene dimer) was investigated using carbon-14 labeled AKD. A solvent sizing method was used to control the amount retained on paper and to achieve even distribution of AKD. The reaction ratio and sizing degree increased with relative humidity up to 80% due to the favorable exposure of AKD lactone rings for reaction. Higher relative humidity had an adverse effect most likely due to the increased separation distance between AKD and the hydroxyl groups of cellulose. The contribution of unreacted AKD on sizing efficiency relative to reacted AKD was found to depend on the amount of reacted AKD present in the paper. The maximum sizing efficiency of unreacted AKD was observed when the sheet contained 0.025% of reacted AKD.