Modification of kaolinite by surface polymerization

Abstract

Abstract Kaolinite filler surfaces were modified by both surface adsorption and surface reaction. Their subsequent wetting and adhesion properties were determined by measurement of the contact angle of the powders by the Washburn technique using three probe liquids that spanned molecular polarity. Surface modification by adsorption utilized the kaolinite surface acidity to polymerize styrene. Surface reaction involved reaction of kaolinite hydroxyl groups with aryl diisocyanates and subsequent termination with a series of alcohols of increasing complexity. It was shown that kaolinite surfaces could be modified to produce surfaces of controlled hydrophobicity that could exceed that of conventionally silanated kaolinite. The ability of phases to spread and wet these filler surfaces was analysed in terms of the thermodynamic functions—spreading coefficient S 12 and spreading pressure π e .