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.