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

Abstract

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.