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 nanocomposite. 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. Polym. Eng. Sci. 45:52–61, 2005. © 2004 Society of Plastics Engineers.

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This paper reviews some of the recent developments of microcellular injection molding, which is capable of producing parts with excellent dimensional stability using lower injection pressure, shorter cycle time, and less material. Process conditions as well as nano/micro-fillers such as nanoclay and core–shell rubber have a strong influence on cell density and cell size, hence, the final material properties of the molded parts. The addition of nano/micro-fillers at optimum loading levels can generally facilitate the formation of microcellular plastics with higher cell density and smaller cell size leading to superior mechanical properties. The novel integration of a solid plastic surface with a microcellular plastic core via the co-injection molding technique has been investigated to achieve Class “A” surfaces and improved material performance. An improved mathematical model has been developed to simulate the cell growth behavior in the microcellular injection molding process.

In this study, polylactide (PLA)-multi-walled carbon nanotube (MWCNT) nanocomposites were melt-compounded using a twin-screw extruder. Solid and microcellular tensile bar specimens were produced via conventional and microcellular injection molding, respectively. Various characterization techniques were applied to study the static and dynamic mechanical properties, degree of MWCNT dispersion, cell morphology, and crystallization behavior. The addition of a small amount of MWCNTs led to a decrease in the cell size and an increase in the cell density of the microcellular PLA specimens. A transmission electron microscopy analysis of the PLA-MWCNT specimens revealed a higher degree of MWCNT dispersion in the microcellular PLA-MWCNT composite compared with its solid counterpart, indicating that the microcellular injection molding process further dispersed the MWCNTs. For both solid and microcellular specimens, the addition of 1.5 wt% MWCNTs reduced the specific strength, specific toughness and strain-at-break while exerting less impact on the specific modulus. The storage modulus was not affected significantly with the addition of MWCNTs, but was found to be higher for the microcellular specimens compared with their solid counterparts. Finally, the crystallinity of PLA increased with the addition of MWCNTs. 418 Carl Hanser Verlag, Munich Intern. Polymer Processing XXII (2007) 5

This article presents the development and characterization of transparent poly(styrene-r-maleic anhydride) (SMA)/alumina nanocomposites for potential use in optical applications. Chemically treated spherical alumina nanoparticles were dispersed in an SMA matrix polymer via the solution and melt-compounding methods to produce 2 wt % nanocomposites. Field emission scanning electron microscopy was used to examine the nanoparticle dispersion. When the solution method was used, nanoparticle reagglomeration occurred, despite the fairly good polymer wetting. However, through the coating of the alumina nanoparticles with a thin layer (ca. 20 nm) of low-molecularweight SMA, reagglomeration was absent in the melt-compounded samples, and this resulted in excellent nanoparticle dispersion. The resultant nanocomposites were semitransparent to visible light at a 2-mm thickness with improved UV-barrier properties. Their impact strengths, tensile strengths, and strains at break were slightly reduced compared with those of their neat resin counterpart, whereas a small enhancement in their moduli was achieved.

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This article presents the study of melt compounding of polystyrene (PS) with various types of titanium dioxide (TiO 2 ) nanoparticles and surfactants, using a corotating twin screw extruder with multiple screw element configurations. It was found that a properly designed high shear screw configuration and the copolymer of silicone, ethylene oxide, and propylene oxide-based surfactant produced the greatest degree of nanoparticle dispersion in PS/TiO 2 nanocomposites, whereas a silane-based surfactant and silicon dioxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ) coated TiO 2 nanoparticles yielded nanocomposites with the least photocatalytic degradation effects and the best retention of tensile and impact properties. POLYM. COM-POS., 28:241-250, 2007.

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