Phase Separation and Crystallization Behavior in Extruded Polypropylene/Ethylene-Propylene Rubber Blends Containing Ethylene-α-Olefin Copolymers

Liquid-liquid (L-L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene-propylene rubber (EPR)/ethylene-α-olefin copolymer (ECP) ternary blends obtained by melt extrusion were investigated by time-resolved light scattering (TR-LS) and optical microscopy. L-L phase separation via spinodal decomposition (SD) was confirmed by TR-LS data. After L-L phase-separation at 250°C for various durations, the blend sample was subjected to temperature-drop to 130°C for isothermal crystallization and the effects of L-L phase separation on crystallization were investigated. Memory of L-L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L-L phase-separated time at 250°C. Slow crystallization for the long L-L phase-separated time could be ascribed to decrease in chain mobility of PP by decrease in rubbery components in the PP-rich region. The ethylene-octene copolymer exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing.