Rheology of highly filled natural CaCO3 composites. II. Effects of solid loading and particle size distribution on rotational rheometry

Abstract

AbstractSuspensions of poly(dimethyl siloxane) containing various loadings of natural CaCO3 particles, of several particle size distributions, were studied using capillary rheometry. Highly loaded suspensions were characterized, emphasizing their unique rheological behavior. Shear thinning was observed mainly for suspensions with solid loading close to the maximal volume fraction, significant at low frequency and becoming negligible at 1 decade higher frequency. The Cox‐Merz rule was found valid for suspensions containing up to nearly 40 vol% particles. The viscosity was unaffected by particle size up to roughly 40 vol% particles as well. However, the dominancy of particle size distribution was demonstrated by the relative viscosity; fine filler suspensions exhibited much higher viscosity at a given loading. Equivalently, the maximal solid loading of coarse unimodal and of bimodal particle size distributions was significantly higher than the one of fine unimodal suspensions. Fair agreement with the Chong and Krieger‐Dougherty (k = 2.5) models was found for unimodal suspensions, while the combined Farris‐Chong model showed a much better fit for the bimodal suspensions. A unique behavior of the high volume fraction suspensions is the liquid solid transition that is defined by the crossover of G′ and G″ as function of frequency curves. Nevertheless, tan δ as a function of frequency curves for all studied compositions showed positive slopes, which is characteristic of solid‐like materials. POLYM. COMPOS., 28:524–533, 2007. © 2007 Society of Plastics Engineers