Relative Efficacy of the Functional Groups in the Adsorption Process

The relative efficacy towards adsorption on TiO₂ pigment of the organic functional groups, viz. carboxyl, hydroxyl, ester and unsaturation which are commonly encountered in polymeric materials like alkyd resins, was determined from the sedimentation rate of pigment particles dispersed in the solution of simpler molecules like stearic acid, oleic acid, stearyl alcohol and methyl stearate and also from the amount of material adsorbed on pigment. Thejr efficacy was found to be in the order : carboxyl > hydroxyl > ester. The olefinic unsaturation present in the alkyl chain enhanced the adsorption capacity. Alkyl resins which possess such functional groups in varying proportions showed their efficacy towards adsorption on TiO₂ and stability of pigment dispersion in the following order: conventional alkyd (generally with excess hydroxyl functionality over carboxyl) > caiboxyl blocked alkyd > hydroxyl blocked alkyd > both carboxyl and hydroxyl blocked alkyd.