Dispersion mechanisms in aqueous alumina suspensions at high solids loadings

A poly(acrylic acid), a lignosulphonate and a comb copolymer were compared as dispersants for highly concentrated aqueous alumina suspensions. The aim was to compare the stabilization efficiency of the dispersants at normal processing conditions (pH 9–10) through rheological measurements, and to correlate this to stabilizing mechanisms by means of ζ-potential, adsorption and atomic force measurements. Rheological properties of suspensions stabilized with poly(acrylic acid) were superior to those based on the lignosulphonate and the comb copolymer, especially at solids loadings above 57 vol.%. ζ-Potential measurements showed that all three dispersants adsorbed on alumina and lowered the isoelectric point. Both poly(acrylic acid) and lignosulphonate resulted in highly negative ζ-potential at pH 10, whereas low ζ-potential was observed over the whole pH range with the comb copolymer. AFM results indicate that the poly(acrylic acid) and the comb copolymer provide steric repulsion, whereas only electrostatic repulsion could be seen with the lignosulphonate.