Recent years, emission of greenhouse gases discharged by the consumption of fossil fuels are increasing. As a result, huge problems such as global warming and environmental pollution have been created. Therefore, it is important to reduce use of fossil fuels and develop the alternative to petroleum. Poly(lactic acid) (PLA) is a biomass and biodegradable polymer, which is expected as an alternative material of other polymers. However, PLA has some disadvantages such as high viscosity , high density, low thermal resistance and so on for injection moldings. The use of PLA in injection molding parts is still limited due to these disadvantages. In order to solve these disadvantages of PLA, we have investigated the injection molding of PLA by applying Supercritical Fluid (SCF) technique. In this study, it is revealed that injection pressure decreased to about 60% as compared with conventional injection pressure. And we also discuss the mechanical, thermal and dielectric properties on the basis of the results of tensile test, Izod test, DMA, and dielectric measurement. Specific tensile modulus and strength of specimens decreased on increasing the percentage of foam in the specimens. On the other hand, specific Izod impact strength of specimens didn't decrease. In addition, the value of dielectric constant and loss decreased on increasing the percentage of foam in the specimens. Therefore, by this SCF foaming technique we showed that we can easily produce impact-resistant and low dielectric materials of PLA.

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In this research, we developed and proposed a numerical analysis model mixed with the phase of solid-liquid. It aims to make an accurate estimate of the progress of zero-velocity area with a lower analytical mesh in the through-thickness direction. We focused to improve approximate accuracy about shear rate and friction heat at elements mixed with the phase of solid-liquid including the bounary zone of solid-liquid phase. Pressure loss and filling pattern in molding experiments were used for the confirmation and the evaluation of validity of proposed numerical analysis model. The resulting confirmation of the validity of modeling applied in this research is as follows.
1) Analytical time to obtain the analytical result equal to usual modeling was 1/7, because of decreased degree of freedom.
2) Higher reproducibility of the pressure loss in plate of board thickness 2mm and filling pattern in plate with thickness deviation from 0.5 to 0.2mm was obtained as a result of analysis.

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