Morphology and rheology of PP/POE blends in high shear stress field

Polypropylene (PP)/polyolefin elastomer (POE; ethylene-octene copolymer) blends with varying weight percentages of POE were prepared in a twin-screw extruder and molded through high shear rate injection-molding process. The morphologies and rheology of the PP/POE blends were systematically investigated based on rheological data and experimental analysis. The results indicate that the polymer blends of plastic and rubber in a high shear stress field result in a multilayered microstructure, which can be divided into skin, transitional, shear, and core layers according to the morphology of the dispersed phase. The morphology formation of the dispersed phase depends on the shear field and temperature field in the processing. Morphological evolution of the dispersed POE phases in PP matrix was described and quantified. A dragging ellipsoid model and capillary number were employed to describe the morphological evolution of the dispersed phase, and the morphological parameters were obtained. The results show that the dragging ellipsoid model is well suited to explain the morphological evolution of the dispersed phase in polymer blends molded under high shear rate.