Dynamic rheology and microstructure of polypropylene/clay nanocomposites prepared under Sc-CO2 by melt compounding

Polypropylene (PP)/clay nanocomposites were prepared using a twin-screw extruder with the aid of supercritical carbon dioxide (Sc-CO2). The dynamic rheological properties were measured using a rheometer in the oscillatory mode. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure of extruded nanocomposites. Results showed that an optimized CO2 concentration existed. When the CO2 concentration increased up to the optimized level, the nanocomposites tended to be more viscous, especially at low frequency, whereas further increasing the CO2 concentration resulted in a decrease in the complex viscosity and dynamic moduli. The presence of Sc-CO2 with a concentration not higher than the optimized level was helpful to promote the degree of dispersion of the nano-clay in PP matrix, but overloading of CO2 would have a negative effect on the clay dispersion.