Rheological behavior of highly filled EPDM compounds with calcium carbonate, carbon black, silica and zinc oxide

The shear viscosity, creep and constant shear rate transients have been measured for 0.20 volume fraction compounds of an EPDM with calcium carbonate, carbon black, silica anti zinc oxide of similar particle size at 100 degrees C. Measurements have been made in a creep sandwich instrument, pressurized rotational rheometer and a capillary rheometer and cover nine decades of shear rate. All of the compounds exhibit enhanced viscosities and yield values; i.e. there are stresses below which there is no flow. The greatest yield values and increased viscosities are with the compounds with calcium carbonate and zinc oxide. More extensive studies were made with the EPDM-calcium carbonate system, where it was shown that increasing particle size reduces shear viscosity and yield values. Further, surface treating calcium carbonate with stearic acid significantly reduces the shear viscosity and yield value of the corresponding EPDM compound.