Alkyl ketene dimer and precipitated calcium carbonate interactions in wet-end papermaking

This thesis investigates the interactions between alkyl ketene dimer (AKD) and precipitated calcium carbonate (PCC). Although the mechanisms behind AKD sizing and reactions with cellulose have been studied in-depth, methods describing AKD retention are poorly understood. The aim of this research was to determine the conditions and time-scale under which AKD and PCC heteroflocculate, and to determine the influence of PCC on non-retained AKD. We also wanted to understand the mechanisms behind AKD interactions with cPAM, and perform experiments on the twin-wire sheet former. We outline a procedure for creating an AKD emulsion coated by cationic starch and free of extraneous substances. We find that AKD and PCC each homoflocculate, but no heteroflocculation occurs between the two chemicals. This suggests that PCC and AKD do not directly interact. Instead, starch removal from the AKD particle surface aids the homoflocculation of PCC (via polymer bridging). This indicates that the alkaline environment is the most significant factor contributing to AKD hydrolysis. More importantly, we find that AKD and PCC are not likely to interact in the whitewater cycle. This refutes the general idea that PCC lowers AKD retention. Adsorption kinetic experiments revealed that although cationic AKD and cPAM do not flocculate, cPAM does increase the retention of AKD by assisting its deposition onto fibers. Asymmetrical polymer bridging explains both the increase in AKD retention and the behavior of AKD flocculation kinetics with cPAM. Although the initial kinetics are nearly independent of cPAM dosage, excess cPAM delays the achievement of maximum possible AKD retention due to starch and cPAM re-conformation. Lastly, it was found that the addition of cPAM results in an increase in the bond strength between AKD and fibers, thereby eliminating AKD detachment. Studies on the twin-wire sheet former found that cPAM increases the first-pass retention of AKD three-fold. The twin-wire former was proven to be a useful tool for studying AKD retention.