AKD spreading phenomena on chemically heterogeneous surfaces

The AKD sizing mechanism is complex and still not well described, despite many attempts to identify contributing factors to the overall mechanism. Given the chemical heterogeneity of paper substrates, the current study examined possible effects of this heterogeneity on AKD spreading. Model patterned surfaces using an IGT F1 printability tester were prepared on glass, cellulose-coated glass, cellulose fibre and glass fibre substrates. For the non-porous substrates, results showed an affinity of AKD to the more hydrophilic regions on the surface, or equivalently those with higher surface energy. Less AKD spreading was observed on the low surface energy regions. Significant wetting of AKD onto porous substrates was observed, indicating that mechanical roughness and porosity are also dominant factors. Patterns applied to these substrates however did not penetrate through the entire depth of the substrate, possibly affecting the results obtained. XPS results of paper handsheets made with various quantities of AKD, starch and filler suggested a weak trend towards enhanced AKD distribution at the surface with lowering amounts of additive. These results were verified with the Cobb test method. While it is unlikely that AKD exhibits a wetting or spreading phenomenon in the true sense, it does appear that chemical heterogeneity is one of many contributing factors in the overall sizing mechanism.