Microstructure and crystallography in microcellular injection-molded polyamide-6 nanocomposite and neat resin

The effects of adding nanoclay to polyamide-6 (PA-6) neat resin, and the effects of processing parameters on cell density and size in microcellular injection-molded components were investigated. In addition, the crystal sizes, structures, and orientation were analyzed with the use of x-ray diffraction (XRD) and a polarized optical microscope. The standard ASTM D 638-02 tensile bars for the analyses were molded according to a fractional four-factor, three-level, L9 Taguchi design of experiment (DOE) with varying melt temperature, injection speed, supercritical fluid (SCF) concentration, and shot size. It was found that the presence of montmorillonite (MMT) nanoclay greatly reduced the size of the cells and crystals, but increased their density in comparison with neat resin processed under identical molding conditions. In addition, at the sprue section downstream of the machine nozzle, cell size gradually decreased from the part center toward the skin for both the neat resin and the nanocomposrte. It was also found that shot size was the most important processing parameter for both the neat resin and nanocomposite in affecting cell density and size in microcellular injection molding components. Weakly preferred crystal orientations were observed on the surface of microcellular injection-molded PA-6/MMT tensile bars. Finally, the addition of nanoclay in PA-6 neat resin facilitated the formation of γ-phase crystals in the molded components.