Polymer Adsorption Effects on Structure and Rheological Properties of Concentrated Suspensions of Talc Particles

Abstract

The adsorption of a polyacrylate sodium salt (PANa) onto talc and its influence on the dispersion of the particles is investigated both in dilute suspensions (adsorption isotherm, ion titration, and electrophoretic mobility) and in concentrated dispersions (rheology). The adsorption of negatively charged dispersant on the negative surface of talc remains possible through a charge compensation effect of PANa with Ca²⁺ ions originating from the dissolution of carbonated impurities in the talc samples. It is evident that the prevailing mechanism of adsorption involves a bridging process through Ca²⁺ cations between the negatively charged surface and the negative macromolecule. The adsorption analysis of the PANa is then correlated with the rheological behavior of the concentrated suspensions of talc particles. Evolution of the viscosity of the suspensions suggested the polymer was able to improve the dispersion of solid particles in concentrated suspension. In another part, the influence of associative thickeners, such as polyacrylic acid with different degrees of grafted alkyl chains of various lengths, on the stability of concentrated talc dispersions was investigated by rheology. These associative thickeners act as stabilizing agents against the sedimentation of the talc particles through formation of a 3D macromolecular network. This 3D structure allows for the gelification of the suspensions above a critical concentration of associative thickener, depending both on the hydrocarbon chain length and the degree of grafting. The rheological behavior of gel‐like structure was investigated in detail. Finally, a qualitative model is proposed in which the dispersed talc particles are trapped in the associative network, thus greatly slowing their sedimentation.

Keywords:

• Adsorption
• Associative thickeners
• Polyacrylate sodium salt
• Rheology
• Concentrated suspension
• Dispersion

Acknowledgments

The authors wish to acknowledge Talc de Luzenac S.A (France) for financial support and R. Baeza for fruitful discussions.