Fracture resistance and micromechanical deformations in PP/PA6/EPDM ternary blends: Effect of rubber functionality, dispersion state and loading conditions

Polypropylene (PP)-based ternary blends comprising 15 wt% polyamide 6 (PA6) and 15 wt% of either reactive or nonreactive ethylene-propylene-diene monomer (EPDM-g-MA or EPDM) rubber were prepared. A core-shell morphology was observed for reactive blends while nonreactive blends showed separately-dispersed morphology. The role of phase morphology, interfacial strength and dispersion state of the modifier particles in reactive blends (via applying different processing methods) on the fracture resistance of the resulting blends under both Izod impact and quasi-static fracture tests were clarified. The impact strength of reactive blends was significantly higher than that of nonreactive ones and strongly dependent upon the mixing procedure. The crack resistance of the blends was further studied by the essential work of fracture (EWF) method. The specific EWF (we) and non-EWF (βwP) values of nonreactive blend were interestingly higher than those of the reactive blends. The contributions of yielding (we,y and βywp,y) and subsequent tearing (we,t and βtwp,t) components on the fracture works were determined. The percolated structure of the core-shell particles exhibited superior fracture resistance under fracture tests. Multiple void-fibrillar structures were developed in the reactive blends. A synergistic effect of cavitation inside rubber particles and debonding-cavitation around the PA6 domains was observed in the nonreactive blend.