An AKD emulsion size was treated to various organic and inorganic materials suspended in water, and the levels of water repellency were evaluated by observing water droplets put on the AKD-treated materials. Barium oxide, bleached kraft pulp, celite, glass wool, calcium carbonate, microcrystalline cellulose powder, talc and titanium dioxide turned to ahve clear water repellency by the AKD treatment more efficiently than alum-emulsion rosin size treatments. The water repellency of these AKD-treated materials was maintained after extraction with chloroforma at 70 deg C for 1 day, but comletely disappeared by extraction with 1 aqueous Tween 80 at 20 deg C for 1 day. On the other hand, active carbon, bentonite, silica gel and white carbon had no water repellency even by the same AKD treatment. The appearance of water repellency depended on neither chemicla structures nor particle sizes of the materials, but there was an inverse correlation between their specific surface areas and the levels of water repellency. Namely, water repellency appeared on the material at 0.4 AKD addition level, when its specific surface area was lower than about 15 m~2/g.
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