Microscopic Deformation Behavior and Crack Resistance Mechanism of Core-Shell Structures in Highly-Toughened PP/PA6/EPDM-g-MA Ternary Blends

Highly-toughened blends, comprising polypropylene, polyamide 6, and maleic anhydride-grafted ethylene-propylene-diene monomer rubber (PP/PA6/EPDM-g-MA), of core-shell morphology are prepared and impact of microstructural development, at different PA6:EPDM-g-MA weight ratios (fixed at 30 wt%), on macroscopic mechanical and fracture characteristics of blends is studied through in-depth analysis of micromechanical deformations operating in the blends. The role of dispersion state of modifier domains on nucleation and evolution of various microscopic deformations accompanying the fracture process under impact and quasi-static fracture tests is closely examined. Increase in EPDM-g-MA:PA6 ratio develops agglomerated core-shell domains in the form of extended island-like structures. While impact data show significant synergistic toughening effect of dispersed composite domains in ternary blends compared with PP/EPDM-g-MA (70/30) binary blend, fracture works show a sole dependence on rubbery fraction. Fractography examinations reveal deformation of dispersed domains, development of multiple voids, and highly deformed craze-like void-fibrillar structures within core-shell structures as well as at their interfaces with surrounding matrix. The importance of deformation zones in activation and promotion of matrix shear yielding is clarified, while their function as crack nucleation and subsequent crack propagation trajectories is highlighted. The stability of void-fibrillar zones is found essential for extensive plastic deformation and premature failure prevention.

Automated summary

The study investigates the impact of microstructural development at different PA6:EPDM-g-MA weight ratios on the macroscopic mechanical and fracture characteristics of highly-toughened blends. It is found that an increase in EPDM-g-MA:PA6 ratio leads to the formation of agglomerated core-shell domains. The fracture works reveal a sole dependence on rubbery fraction, while impact data show a significant synergistic toughening effect of dispersed composite domains in ternary blends compared with binary blends.