Foam injection molding is a molding method that generates cells in the resin by dissolving carbon dioxide and chemical foaming agent. Foam injection molding makes it possible to reduce weight of products and material by generating cells in the resin. However, this technique may cause a problem defective molded product was a defects known as short-shot if the amount of resin that is filled into the mold is insufficient. Therefore, in this study, we studied to prevent the molding defects such as short shot, and to clarify molding conditions and factors to achieve stable molding process in continuous molding. Foam injection molding with a thermoplastic elastomer and supercritical carbon dioxide was carried out. We considered molding conditions and factors that prevented molding defects such as short-shot and could realize a stable molding process. We have revealed the following results. When carbon dioxide gas was injected at a pressure lower than the critical point, weight of the resin was constant and the weight of the molded product was stable. Therefore, we could achieve a stable molding process, and prevent short-shot. However, in this case, it is necessary to use a gas having a high-solubility into the resin.

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More than one billion tons of banana leaves are discarded per year. Banana fibers can be made from banana leaves. In the present study, banana fibers without being processed (BF), banana fibers with an alkali treatment (BF-A), banana fibers treated in an alkali aqueous solution with tension (BF-AT), and poly(butylene succinate)(PBS) were used to make BF/PBS composites, BF-A/PBS and BF-AT/PBS composites by applying a twin screw extruder, respectively. The specimens were prepared using an injection molding machine. The three-point flexural test and the charpy impact test were conducted. The results of three-point flexural test showed that when the weight fraction of banana fibers was increased in composites, both flexural strength and flexural modulus increased. Flexural strength and flexural modulus of composites containing BF were higher than in composites containing BF-A. Flexural strength and flexural modulus of composites containing BF were higher than in composites containing BF-AT. The results of charpy impact test showed that when the weight fraction of banana fibers was increased in composites, impact strength increased. Charpy impact strength of composites containing BF-A was higher than that of composites containing BF. Charpy impact strength of composites containing BF-AT was higher than that of composites containing BF-A. The reason was verified that the surface treatment on banana fibers enhanced the polymer wettability and increased the broken-out displacement of composites.

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