Alkyl Ketene Dimer (AKD) sizing treatment and charge interactions in recycled paper

Alkylketene dimer (AKD) sizing dispersions from two commercial sources, in addition to the corresponding laboratory-produced AKD dispersions, were investigated relative to their usage in a recycled office waste furnish. Two main sets of experiments were carried out. One set involved testing the pulp after AKD treatment, with the evaluation of dewatering rates, retention efficiency, and charge. The other set involved brightness and water resistance properties when AKD was added in making handsheets. There was generally a positive but decreasing incremental effect of the sizing treatments (dispersions or associated cationic polyelectrolytes) with increased levels of addition, on drainage rate and retention efficiency. AKD treatment resulted in increased brightness, which was attributed to increased retention of calcium carbonate and of fluorescent whitening agent in the paper. Less sizing agent was required in the recycled furnish compared to the virgin fibre. Results were consistent with the charged character of the emulsified AKD formulations.