Study On Morphology, Properties And Toughening Mechanism Of Sandbag Microstructure-Toughened PA6/EPDM/nano-CaCO₃ Ternary Composites

Polyamide 6 (PA6) is a kind of widely used engineering plastics, but the application is limited because of its poor toghness under low temperature. In this work, ethylene propylene diene terpolymer rubber (EPDM)/maleated ethylene propylene diene terpolymer rubber (EPDM-g-MAH) was employed as rubber, nano calcium carbonate (nano-CaCO₃) was employed as inorigid particles,"sandbag"microstructure particle embedded nano-CaCO₃ agglomerate into EPDM was constructed in PA6/EPDM/nano-CaCO₃ ternary composites. This"sandbag"microstructure could effectively improve the toughness of PA6. Morphology evolution of"sandbag"microstructure particles in PA6 matrix and under the external force was studied by Scanning Electron Microscope (SEM) and Dynamic Mechanical Analysis (DMA). The toughening mechanism of"sandbag"microstructure particles was further discussed. The main works and conclusions were listed as follows:1. The effect of interfacial properties controlled by modifing the surface properties of nano-CaCO₃ and crosslinking degree of EPDM on morphology and properties of the ternary composites were studied. It was found that nano-CaCO₃ coated with stearic acid was selectively distributed in EPDM, and"sandbag"microstructure was constructed in the ternary composite of well toughness; When the content of dicumyl peroxide (DCP) in EPDM increased from 0 wt% to 0.30 wt%, the size of"sandbag"microstructure particles dispersed in PA6 matrix became larger, while the impact strength of the ternary composites became smaller. When the ternary composite was impacted, the impact energy applied on the composite was dissipated by the fiber-forming mode and dilataional bands which were induced by"sandbag"microstructure particles finely dispersed in PA6 matrix.2. The influence of compounding routes and injection molding conditions on morphology and properties of PA6/EPDM/nano-CaCO₃ ternary composites was studied. It was found that the"sandbag"microstructure particles could be constructed only via two-step compounding route, and"sandbag"microstructure particles were effective to improve the fracture toughness and resist the growth of the crake. The structure integrity of"sandbag"microstructure particles dispersed in PA6 matrix markedly depended on the injection rate, when the injection rate increased, there was nano-CaCO₃ agglomerate present in the skin layer, the dispersion of"sandbag"microstructure particles in the core layer became worse, and the impact strength of the ternary composites became smaller.3. The mechanism of energy dissipation which includes voids and plastic deformation of matrix was studyed. Various modes of voids were observed by scanning electron microscope (SEM). The volume of voids in PA6/EPDM/nano-CaCO₃ (two-step) ternary composites (E4) was larger than PA6/nano-CaCO₃ binary composites (E1), PA6/EPDM binary composites (E2) and PA6/EPDM/nano-CaCO₃ (one-step) ternary composites (E3). The fracture surface along the direction perpendicular to the tensile direction observed by SEM resulted that matrix plastic deformation of E4 was larger than E1, E2 and E3. So energy dissipation of E4 was larger than E1, E2 and E3.