Study on morphology of ternary polymer blends. I. Effects of melt viscosity and interfacial interaction

The morphology of some ternary blends was investigated. In all of the blends polypropylene, as the major phase, was blended with two different minor phases ethylene-propylene-diene terpolymer (EPDM) or ethylene-propylene-rubber (EPR) as the first minor phase and high-density polyethylene (HDPE) or polystyrene (PS) as the second minor phase. All the blends were investigated in a constant composition of 70/15/15 wt %. Theoretical models predict that the dispersed phase of a multiphase polymer blend will either form an encapsulation-type phase morphology or phases will remain separately dispersed, depending on which morphology has the lower free energy or positive spreading coefficient. Interfacial interaction between phases was found to play a significant role in determining the type of morphology of these blend systems. A core-shell-type morphology for HDPE encapsulated by rubber was obtained for PP/ rubber/PE ternary blends, whereas PP/rubber/PS blends showed a separately dispersed type of morphology. These results were found to be in good agreement with the theoretical predictions. Steady-state torque for each component was used to study the effect of melt viscosity ratio on the morphology of the blends. It was found that the torque ratios affect only the size of the dispersed phases and have no appreciable influence on the type of morphology. (C) 2001 John Wiley & Sons, Inc.