Journal of Cellular Plastics

The effects of nanoclay addition into polyamide-6 (PA-6) neat resin and processing parameters on cell density and size in microcellular injection molded components are investigated. The analyses are performed on the sprue section of standard ASTM D 638-02 tensile bars molded based on a fractional four-factorial, three-level, L9 Taguchi design of experiments (DOE) with varying melt temperature, injection speed, super critical fluid (SCF) concentration, and shot size. It is found that the presence of nanoclay greatly reduced the cell size and increased the cell density when compared to neat resin processed under identical molding conditions. In addition, cell size distribution at the sprue center was, in general, the largest, gradually decreasing toward the skin for both the neat resin and the nanocomposite. Finally, in contrast to neat resin, in which shot size and injection speed were important to cell density and all molding parameters affected cell growth, the cell size and density for nanocomposite only depended strongly on shot size.

This paper presents the effects of processing parameters and submicron core-shell rubber particle filler on the mechanical properties and cell morphology of microcellular injection molded polyamide-6 (PA-6) composites. Three types of materials are studied, namely, neat PA-6 resin, and 0.5 wt% and 3.1 wt% core-shell rubber polybutylacrylate-polymethylmethacrylate-filled PA-6 composites. This study shows that the addition of a small amount (0.5%) of core-shell rubber particles improved the ductility and impact strength of micro-cellular injection molded PA-6 samples. In comparison to the microcellular injection molded PA-6 polymer-clay nanocomposite, the samples with a small amount (0.5%) of core-shell rubber had much higher impact strength and ductility. The small addition of core-shell rubber also reduced cell size and increased cell density of the microcellular injection molded PA-6 parts, in comparison to their neat resin counterparts. On the other hand, at higher core-shell rubber loading, the cell size and density were found to be similar to that of the neat resin.

The crystallization behaviors of polyamide-6 (PA-6) and its nanocomposites undergoing the microcellular injection molding process are studied using Transmission Electron Microscopy (TEM), X-ray Diffractometer (XRD), Polarized Optical Microscopy (POM), and Differential Scanning Calorimetry (DSC). The relationships among the morphology, the mechanical property of the molded parts, and the crystallization behavior are investigated. With the addition of nanoclays in microcellular injection molded parts, the growth of the γ-form crystal is suppressed and the formation of γ-form crystals is promoted. Both nanoclay and dissolved gas have a big influence on PA-6 crystalline structures. The existence of nanoclay increases the initial crystallization rate. But with extra addition of nanoclays in the polymer matrix, the increase of crystallization rate is reduced. Microcellular injection molded nanocomposites with proper amount of nanoclays possess the maximum crystallization activation energy and produce a finer and denser microcell structure which leads to better mechanical properties.

Solid-state viscoelastic shear moduli (G0 and G00) of cylindrical polymer foams are measured as a function of frequency. Extruded samples are produced via a cylindrical die to obtain foams of various morphologies. To perform the shear measurements, a modification of the torsion rectangular setup on an ARES rheometer is made. The setup, calibration, and test conditions are presented. The data are discussed and compared to simple models taken from the literature.

This work examines four polystyrene (PS) resins and PS resins with fillers. The materials are processed into sheets and then the sheets are foamed at various supercritical conditions. The morphology of the foam is studied and a large porous PS foam is also developed for a vacuum insulation panel.