Interaction of binders with dispersant stabilised alumina suspensions

The rheological response of selected aqueous alumina suspensions, stabilise d with a polyelectrolyte or with an organic polyvalent salt dispersant, and including poly(vinyl) alcohol (PVA) as a binder, are described in this stu dy. The polymer dispersant was composed of an ammonium salt of poly(methacr ylate) and the organic polyvalent compound was a sodium salt of an aromatic sulphate. The results show that the addition of PVA, without any included dispersant does not significantly influence the rheology of the system. How ever, in the presence of a dispersant the rheology is greatly affected. At a given concentration of the dispersant, the viscosity, storage and loss mo duli all increase, as the PVA concentration is increased. Also, for a given concentration of the PVA, it is observed that the viscosity, storage and l oss moduli values increase as the concentration of the dispersant is increa sed. It is argued that at low PVA concentrations, an excess concentration o f the unadsorbed dispersant causes flocculation of the particles in the sus pension by a reduction of the repulsive electrostatic (double layer) effect . In contrast, at higher concentrations of the PVA the flocculation of the suspension is promoted via a depletion mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.