Online shear viscosity and microstructure of PP/nano-CaCO3 composites produced by different mixing types

In this work, the online melt shear viscosity of polypropylene/nano-calcium carbonate composites was measured during the compounding to investigate the relationship between their rheological behavior and microstructure. Effects of dispersive mixing, distributive mixing, and chaotic mixing on online shear viscosity and microstructure of nanocomposites were analyzed. The results showed that the online shear viscosity of nanocomposites is lower than that of pure PP, when the nano-CaCO3 content is lower than 5, 10, and 15 wt%, compounded by high dispersive mixing, dispersive/distributive mixing, and dispersive/distributive/chaotic mixing, respectively. This is greatly related with the dispersion of nanoparticles in PP matrix. It is deduced that there exists a critical percentage (Φcr) of the nano-CaCO3 with size lower than 100 nm and a critical mean diameter (dcr). The shear viscosity is lower than that of pure PP when the percentage is higher than the critical percentage and the mean diameter is lower than the critical diameter. In this work, the critical percentage is 80% and critical mean diameter is 60 nm.