Models for the rheology of clay-GCC coating colors

Abstract

Modifications to standard models from the literature were used to predict the viscosity and apparent yield stress of coating suspensions as functions of shear rate and solids content. An experimental investigation was also carried out to obtain the required experimental data. The impact of the key factors, viz. particle-particle interactions, pigment properties and binder system was examined. The pigment type significantly affected the coating rheology due to modifications in the coating suspension microstructure. The partial replacement of latex by starch only reduced the viscosity and yield stress of coating colors based on ground calcium carbonate (GCC). However, the partial replacement of the binder did not affect the rheology of clay-based coating colors. A modified Maron-Pierce correlation was used along with the apparent yield stress to obtain the maximum packing fraction of the suspensions under low shear conditions. A Casson-type 3-parameter model was also developed. This model is capable of fitting the data over the entire range of shear rates, including the apparent yield stress region of the structured materials. All the model parameters bear physical meanings.