Role of polymeric dispersant functional groups in the dispersion behaviour of titania pigment particles

The adsorption of polymeric dispersants onto titania pigment particles has been investigated at pH 9.5 as a function of the type of polymer functional group, using polyacrylic acid and modified polyacrylamides. The polyacrylamides include homopolymer and copolymers with either hydroxyl groups or carboxylate and hydroxyl groups. The experimental methods used were adsorption isotherm, zeta potential, particle size measurements and theology. The anionic dispersants increased the magnitude of the titania pigment particle zeta potential, while the nonionic dispersants had a negligible effect. Both polyacrylic acid and polyacrylamide copolymers altered the titania pigment dispersion behaviour, reducing the suspension yield stress and the mean pigment particle size, while the polyacryl-amide homopolymer had a negligible effect on the pigment dispersion properties. Generally the optimum dispersion effect (minimum particle yield stress and particle size) coincided with the polymer adsorption density; however, for polyacrylic acid, the maximum dispersion effect occurred prior to maximum adsorption. Acrylamide polymer functional groups adsorbed onto the pigment surface but they were unable to influence the pigment particle dispersion properties; however, adsorption and dispersion properties were enhanced in the presence of hydroxyl groups.