An experimental investigation of the redistribution behaviour of alkyl ketene dimers and their corresponding ketones

Recent fundamental studies on the mechanism of AKD sizing have been undertaken to address the current lack of understanding in this area. These studies have shown that during sizing, AKD does not spread on the surface of a fibre via complete wetting (i.e. macroscopic contact angle=0°). Several processes, such as capillary wicking, evaporation–redeposition and surface diffusion of an autophobic precursor, have been identified as contributing to the migration of AKD on a cellulose fibre surface. Recently, it has been suggested that migration of the autophobic precursor on a hydrophilic substrate may be due to the melting point of AKD in a two-dimensional mono-molecular layer being lower than that of bulk AKD wax. In this work, we present experimental evidence that supports this view. Our results show that the multi-molecular secondary spreading front of AKD behind the primary autophobic precursor is also non-solid at ambient temperature. Molecules in the non-solid AKD film on glass and cellulose surfaces are expected to have a higher mobility than those in solid AKD and are expected to spread more easily. Spreading is not the only factor that determines the level of sizing. It is important that the sizing molecules take up energetically favorable orientations on the substrate surface. When comparing the spreading behaviour of AKD and ketone on glass and cellulose surfaces, it is possible to show that both AKD and ketone are quite strongly adsorbed on a glass surface. However, on a cellulose surface, whilst AKD shows strong adsorption, ketone appears to have a weaker adsorption. The spreading behaviour of ketone on the surface of a cellulose film suggests that the molecular orientation of ketone on cellulose is energetically unfavorable for sizing.