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The influence of ketone (hydrolyzed AKD), spreading promoter and type of spreading substrate on the spreading of AKD molecules by surface diffusion in the form of autophobic precursor was investigated. The effect of the ketone on the rate of the AKD precursor spreading at temperatures below 81 deg C was not significant. Pure ketone also showed precursor spreading. Monolaurin, a spreading promotor, was observed to enhance the spreading rate of AKD. This effect was particularly noticeable for solid AKD (m.p. 51 deg C). Surface diffusion of AKD was also observed to occur on cellophane and on laboratory paper sheets made of bleached or unbleached kraft pulp. The spreading diameter was irregular on the latter surface probably due chemical and physical heterogeneity. The results also showed that AKD monolayer spreading on calcium carbonate and kaolin was limited, probably due to roughness and porosity. However, AKD, and in particular ketone spreading was seen on the smooth, freshly cleaved surface of crystalline calcium carbonate. As expected, ASA wets a hydrophilic silica surface in contact with air to a greater extent than a hydrophobic one. Moreover, ASA spread faster on a calcium carbonate surface conditioned at 90 percent relative humidity than on a nearly dry surface. Thus, it is clear that humidity enhances the spreading of ASA and explains the rapidity of ASA sizing. ASA also showed spreading on the model silica surface through surface diffusion. The spreading was slower in the presence of calcium ions on the silica surface.