Largely improved impact toughness of PA6/EPDM-g-MA/HDPE ternary blends: The role of core–shell particles formed in melt processing on preventing micro-crack propagation

Compared to PA6/EPDM-g-MA binary blends, considerable improvement in the notched impact toughness was achieved in PA6/EPDM-g-MA/HDPE ternary blends in which core–shell structure formed during melt blending, and its toughening mechanism was investigated in this work. Two processing methods were applied to prepare the PA6/EPDM-g-MA/HDPE ternary blends, to obtain core–shell structure with different thickness of EPDM-g-MA shell. A series of PA6/EPDM-g-MA binary blends were also prepared to study the difference of toughening mechanism between pure rubber particles in PA6/EPDM-g-MA binary blends and core–shell particles in PA6/EPDM-g-MA/HDPE ternary blends. It is found that the notched Izod impact strength of a two-step method sample 70/15/15 PA6/EPDM-g-MA/HDPE ternary blend with core–shell structure is 73 kJ/m2, which is 4–5 times higher than a 70/30 PA6/EPDM-g-MA binary blend, and 9–10 times higher than pure PA6. Experiments, including X-ray diffraction, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), double-notch four-point-bend (DN-4-PB) and the essential work of fracture (EWF) tests were performed to study the toughening mechanism of PA6 ternary blends with core–shell structure. The results suggest that the fibrillation of core–shell particles in PA6/EPDM-g-MA/HDPE ternary blend, as “Particles Bridge”, can absorb fracture impact energy and sustain a higher stress so as to obtain the effect of strain hardening and prevent micro-crack further propagating, and thus obtain higher notched Izod impact strength.