Prediction and evolution of core-shell morphology and their effect on mechanical properties of PP blends

The prediction of phase morphology is highly valuable in designing and regulating the properties of multiphase composites, particularly polymer blends. In this study, we prepared two types of ternary blends, PP/HDPE/EPR and PP/HDPE/EPDM composites and compared and analyzed the predicted and observed phase morphology of blends with different elastomers. Using Palierne and Bousmina equations, we calculated the interfacial tensions between two components in PP blends and then predicted the relationship between the spreading coefficient, interfacial tension, and phase morphology according to the spreading coefficient theory. Based on our findings, it was observed that the core-shell structure of EPR and EPDM rubber phase encapsulated HDPE core tends to form in PP ternary blends, which aligns with our experimental results. Additionally, SEM morphology observation results revealed a less number of dispersed phases in PP/HDPE/EPR composites with the same composition ratio. It was observed that the shell had a greater thickness due to the difficulty in dispersing EPR with higher viscosity. Mechanical tests indicated that composites with thin-shell and small-core dispersed phases had better toughness. These composites also displayed less yield strength loss under the same impact conditions compared to those with single rubber phases.