Tailoring the impact behavior of polyamide 6 ternary blends via a hierarchical core-shell structure in situ formed in melt mixing

PA6-based ternary blends were prepared by melt blending of HDPE-g-MA and EPDM rubber, in which EPDM with a low and high viscosity was respectively selected to construct different core-shell morphologies. The core-shell morphology evolution was subsequently controlled via quiescent melt annealing. The relationship between the hierarchical core-shell structure and impact behaviors were studied systematically. Right after extrusion, the dispersed domains in low viscosity EPDM blends displayed a single core-shell structure while a multi-core structure with multiple HDPE-g-MA particles exists within the EPDM2 phase formed in high viscosity EPDM blends. During annealing, the lower viscosity EPDM blends displayed a core-shell size coarsening phenomenon without the core-shell morphological type changing. However, for higher viscosity EPDM blends, the initial multi-core structure evolved into a complete EPDM single-core structure after annealing. The notched Izod impact test indicated that the ternary blends with a multi-core structure had much higher impact toughness than that of other blends. The crack-initiation pattern, impact fractured surface and cross-section of the impact surface tests have been performed to study the impact mechanism. The results indicated that HDPE-g-MA particles within the multi core-shell structure could both enhance the core-shell particles strength and enlarge interfacial areas which avoided the rupture and debonding of multi-core particles. Also these core-shell particles could prevent propagation of the crack effectively, thus obtaining higher notched Izod impact strength.