Influence of polymer functional group architecture on titania pigment dispersion

The influence upon adsorption of polymers containing different functional groups on the dispersion behaviour of titania pigment particle has been investigated at pH 6.0 and 9.5. The polymers chosen are polyacrylic acid and modified polyacrylamides including homo and copolymers modified with carboxylate and/or hydroxyl groups. A range of experimental methods including polymer adsorption isotherms, zeta potential, rheology and particle size measurements were used to assess the dispersion effect of the polymers. Adsorption of polyacrylic acid and anionic polyacrylamide copolymers onto the titania pigment surface is greatest when electrostatic repulsion is absent. At low pH values, below the pigment isoelectric point (iep), the adsorption density of the anionic polymers on titania pigment was high whilst at higher pH values, above the pigment iep, the adsorption density decreased. However, the adsorption of non-ionic polymers on titania pigment was less influenced by the pH. The presence of carboxylate functional groups in both polyacrylic acid and anionic polyacrylamide copolymer altered the titania pigment dispersion behaviour, reducing the suspension yield stress and mean particle size. The polyacrylamide homopolymer had negligible effect on the pigment dispersion properties at pH 9.5, while it caused pigment particle aggregation at pH 6.0. The hydroxyl-modified polyacrylamide had also a de-stabilisation effect on the pigment dispersion at pH 6.0, but decreased the yield stress and the mean particle size at pH 9.5. The stabilisation effect of both anionic and non-ionic polymers was pH-dependent. The dispersion properties of the pigment particles are largely predicted by DLVO theory. (C) 2004 Elsevier B.V. All rights reserved.