Stabilisation of titania pigment particles with anionic polymeric dispersants

The stabilisation of titania pigment in dry water-based paint films with anionic polymeric dispersants containing carboxylate groups was investigated. The results were compared to those obtained from rheological analysis of titania pigment suspensions. The polymeric dispersants chosen were polyacrylic acid and polyacrylamides copolymer modified with carboxylate groups. AFM and TEM were used to assess the distribution of the titania pigment particles in the surface and bulk, respectively, of the paint films which were then compared to the gloss and surface roughness of these films.In the absence of a dispersant, the pigment distribution in the paint films was not uniform and relatively large pigment aggregates appeared at the surface, resulting in a rough surface and low gloss. However, anionic polymeric dispersants decreased surface roughness and increased the gloss of the dry paint films, with the dispersant concentration considerably enhancing pigment distribution in the paint films. An inverse correlation of paint film gloss with surface roughness was observed. The optimum pigment distribution in the dry state was found at dispersant concentrations much higher than those needed to obtain minimum yield stress in aqueous suspensions. This suggests that in the dry state, electrostatic stabilisation is substantially reduced or possibly absent, therefore a higher dispersant concentration is needed to achieve pigment stabilisation.