Colloids and Surfaces A: Physicochemical and Engineering Aspects 161 (2000) 243 – 257 Interaction of binders with dispersant stabilised alumina suspensions Asad U. Khan, Brian J. Briscoe, Paul F. Luckham * Particle Technology Group, Department of Chemical Engineering and Chemical Technology, Imperial College of Science, Technology and Medicine, London, UK Abstract The rheological response of selected aqueous alumina suspensions, stabilised with a polyelectrolyte or with an organic polyvalent salt dispersant, and including poly(vinyl) alcohol (PVA) as a binder, are described in this study. The polymer dispersant was composed of an ammonium salt of poly(methacrylate) 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. However, in the presence of a dispersant the rheology is greatly affected. At a given concentration of the dispersant, the viscosity, storage and loss moduli all increase, as the PVA concentration is increased. Also, for a given concentration of the PVA, it is observed that the viscosity, storage and loss moduli values increase as the concentration of the dispersant is increased. It is argued that at low PVA concentrations, an excess concentration of the unadsorbed dispersant causes flocculation of the particles in the suspension 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. © 2000 Elsevier Science B.V. All rights reserved. Keywords: PVA; Suspensions; Binders www.elsevier.nl/locate/colsurfa 1. Introduction The rheological properties of concentrated sus- pensions are complex and much of the early work was phenomenological in nature. Hunter [1 – 3] and Goodwin [4–7] were really the first to relate rheologically determined parameters, the yield value in the first instance and latter the elastic modulus, to the microstructure of the suspension. In this paper, we utilise these ideas to explore the rheological characteristics of ceramic suspensions. Organic binders are an essential component for the effective processing of many commercial high performance ceramics. These binders are used to provide sufficient strength to the body such that the green bodies can be moulded and retained in the desired shape without breaking or damage, before and during sintering. Many ceramic form- ing processes make use of a binder, including those of dry pressing, slip casting, tape casting, extrusion, roll forming, thick film printing, injec- tion and compression moulding. * Corresponding author. Tel.: +44-171-594-5583; fax: + 44-171-594-5604. E-mail address: p.luckham01@ic.ac.uk (P.F. Luckham) 0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0927-7757(99)00374-X