Simplified approach to understanding the mechanism of AKD sizing

Alkyl ketene dimers (AKD) are extensively used in the sizing of paper products. It is generally accepted that during curing, AKD re-distributes on the surface of the fibres via migration. Although the mechanism of AKD re-distribution on the surface of cellulose fibres has been studied extensively, the mechanism that dominates AKD re-distribution has not been fully understood. In this laboratory we attempted a simplified approach for studying the mechanism of the redistribution of AKD. Work presented in this paper is the first part of this investigation in which we sought the answer to the question of whether AKD spreads in the absence of capillary action. For this purpose a glass surface was used as a hydrophilic substrate and the behaviour of AKD wax during the curing process was monitored. Our results suggest that AKD wax (and emulsion) does not undergo `flow-like' spreading on a glass surface during curing. Curing causes deposition of AKD vapour on areas of the glass surface that were initially not covered by the wax. Our results also show that the AKD-sized glass surface is very non-uniform but this does not prevent the sized glass surface from exhibiting a good macroscopic sizing effect.