Synergistic toughening effects of dispersed components in PP/PA6/EPDM ternary blends; quantitative analysis of the fracture toughness via the essential work of fracture (EWF) methodology
The present work reports and investigates the significant rigid toughening, obtained by the incorporation of rigid polyamide 6 (PA6) phase into toughened polypropylene/ethylene propylene diene terpolymer (PP/EPDM) blend, to avoid substantial softening associated with the rubber toughening. The effects of dispersed phase composition and compatibilization using PP g MA, on the microstructure, quasi static fracture toughness, failure mechanisms, and tensile properties were investigated. The fracture properties were characterized in detail by the essential work of fracture (EWF) method. While addition of PA6 into neat PP reduced the fracture toughness, a remarkable monotonic increase in fracture toughness was observed upon the progressive replacement of EPDM with PA6 in PP/EPDM blends. A synergistic toughening effect of dispersed soft EPDM particles and rigid PA6 phase domains was observed, and compared to PP/EPDM binary blend the uncompatibilized ternary blends showed significantly higher fracture toughness values (we) at much lower rubber contents. The deformation micro mechanisms and the critical role of rubber particles in achieving such a synergistic effect was highlighted and discussed by post mortem fractography. Based on the finding that compatibilization reduced the fracture toughness of ternary blends, effective contribution of PP/PA6 interface in activation of different energy absorbing micromechanical deformations was demonstrated. The energy partitioning approach was also employed to provide more insight into energies dissipated for yielding and subsequent tearing of the samples. The results of fracture analysis in conjunction with the tensile data showed a simultaneous toughening and stiffening effect achieved via incorporation of PA6 into PP/EPDM blends. This work could provide a new and deep understanding of rigid toughening effect observed in multiphase systems.