The study of microcellular injection molded polyamide-6 composites

This study aims to explore the processing benefits and property improvements of combining nanocomposites and core-shell rubber composites with microcellular injection molding. The relationships among microstructures, thermal behaviors, mechanical properties, and molding conditions of microcellular nanocomposites were studied. Molding conditions and nanoclay contents were found to have profound effects on cell structures and mechanical properties of polyamide-6 (PA6) microcellular neat resin and microcellular nanocomposites. Microcellular nanocomposites exhibited smaller cell size and uniform cell distribution as well as higher tensile strength compared to the corresponding PA6 microcellular neat resin. Among the molding parameters studied, shot size had the most significant effect on cell size, cell density, and tensile strength. Fractographic study revealed evidence of different modes of failure and different structural features in the fractured regions depending on the molding conditions. The morphology of the crystalline structures determined by the material properties and the molding conditions influenced the cell wall structure and cell surface smoothness. The correlation between cell density and cell size followed an exponential relationship. Supercritical fluid (SCF) facilitated the intercalation and exfoliation of nanoclay in the microcellular molding process. Nanoclay acted as the nucleation agents for both cell and crystal formations. The addition of nanoclay increased the crystallization rate.; Nanocomposites with a proper amount of nanoclay exhibited the maximal magnitude of crystallization activation energy and produced fine and dense microcell structures, which leads to better mechanical properties. Nanoclay and PA6 crystallite lamella exhibited spatially preferential orientation in the parts. Both nanoclay and supercritical fluid lowered the crystallinity of the parts. Microcells improved the normalized toughness of the nanocomposites. The presence of both microcells and nanoclay rather than modifications of crystalline structures had a significant influence on the mechanical properties of the parts depending on the molding conditions.