Dispersion of metal particles into polymer materials by the plasticizing effect of supercritical fluids was investigated. Using supercritical carbon dioxide, a metal precursor of Ag (AgFOD) was infused into polymer materials such as poly (methylmethacrylate) (PMMA), polystyrene (PS) and poly (ethylene terephthalate) (PET). The heat treatment reduced the infused precursor into Ag metal, leading to the formation of a fine particle dispersion layer near the surface of the polymer sample. To investigate the relationship between the infused amount of Ag and sorption of carbon dioxide into these samples, AgFOD was infused in each sample in the temperature range of 35 to 70°C, pressure range of 10 to 30MPa, and infusion time of 0.5 to 4h. It was found that the amount of metal particles infused into polymers via supercritical carbon dioxide had a strong relationship with the sorption of carbon dioxide. Moreover, addition of small amount of acetone as an entrainer to supercritical carbon dioxide could increase the infusion of Ag particles into the inner layer of the samples. It should be noted that metal particle infusion into polymers using supercritical CO₂ might be controlled by manipulating temperature, pressure, infusion time, and amount of entrainer.

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The effect of control factors on microstructure and appearance of injection molded microcellular polystyrene was investigated in this paper. First, a continuous foam processing system was constructed using a screw preplasticating type injection molding machine, which is capable of supplying blowing agent, plasticizing, kneading and maintaining retention time for gas/polymer solution. The feasibility of foam processing with this system was verified. Injection molding control factors that affect cell nucleation and growth were classified and injection velocity, mold temperature, retention time, plunger stroke and dwelling pressure were selected as key variables for this study. The effects of these factors on cell morphology and appearance of microcellular polystyrene were examined and discussed. It was found that cell size decreases and cell density increases with an increase in injection velocity.

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Viscoelastic simulations of bubble growth in Polypropylene physical extrusion foaming were performed. A multi mode PTT model was used for analyzing the dynamic growth behavior of spherically symmetric bubbles with consideration of diffusion of foaming agent. Changes in dissolved foaming agent concentration in polymer and changes in strain of the polymer melt surrounding the bubbles were simulated with Lagrangian FEM. The simulation technique was validated by comparing with bubble growth data, which were experimentally obtained from visual observations of the polypropylene/CO₂ batch foaming system. The simulation results elucidated that strain hardening characteristics of the polymer does not strongly affect the bubble growth rate, the linear vscoelastic characteristics are more influential and the relaxation mode around 0.01s is the important factor in determining bubble growth rate in the early stage of foaming.

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To achieve higher clarity of polypropylene sheets while keeping a certain level of crystallinily and maintaining mechanical properties, supercritical CO₂ (SCF-CO₂) is used when blending a nucleating agent with polypropylene powder. The nucleating agent is initially dissolved in SCF-CO₂ together with an entrainer (1-propanol), and then the polypropylene powder is exposed to the SCF CO₂/entrainer/nucleating agent system. The SCF-CO₂ enhances the diffusivity of the nucleating agent into the polypropylene powder and enables a better dispersion of the nucleating agents in the polymer. The better dispersion increases the number of nuclei and reduces the size of the spherulites. The reduction of spherulite size improves the clarity of the polypropylene sheets. Comparison of the clarity of polypropylene sheets made from SCF-CO₂ treated powder with those made from powder dry-blended with nucleating agents clearly shows the positive effect of the SCF-CO₂ treatment. The experimental results also show that a higher density of SCF-CO₂ increases the clarity of polypropylene sheet and an entrainer, with a solubility close to that of the nucleating agent, is effective for improving the clarity.

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