Properties of Rubber-Modified Polypropylene Impact Blends

Blends of polypropylene (PP) with epoxidised natural rubber (ENR-50) and constant-viscosity natural rubber (SMR-CV) were prepared in a laboratory-scale extruder; the rubber content ranged from 0 to 50%. The mix ing torques increase as the percentage of rubber increases-an indication of in crease in the melt viscosity. After mixing and pelletising, the samples were in jection moulded and tested for mechanical properties. Tensile strength decreases while elongation at break increases as the rubber content in the blends increases. PP/ENR-50 blends show an increase in die swell while PP/SMR-CV blends show a decrease with increasing rubber content. PP/ SMR-CV blends have higher Izod impact strength than PP/ENR-50 blends. Dynamic mechanical analysis (DMA) was used for the compatibility studies and the PP/ENR-50 blends were observed to be more compatible than the PP/SMR-CV blends. The "stable torque" from mixing studies further corrobo rates the compatibility study. Differential scanning calorimetry (DSC) analysis shows that the incorporation of rubber phase into polypropylene has no signifi cant effect on the degree of crystallinity of the blends.