Microcellular foams with unique cellular structures were prepared from poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) blends using a foam injection molding technique with a core-back operation. PLA and PBSA are biopolymers that are partially miscible with each other. When these biopolymers were blended, several blend morphologies appeared that were found to be dependent on the blend ratio. The blend morphologies and thermal and rheological properties of polymer blends with PLA/PBSA ratios of 100/0, 30/70, 50/50, 70/30, and 0/100 were observed, and the cellular structures of their foams were investigated. While most of the polymer blends showed sea and island structures, a polymer blend with a PLA/PBSA ratio of 50/50 showed a layered structure for the two polymers in which the continuous phases of both polymers were elongated along the flow direction used for injection molding. By utilizing the unique blend morphology and the difference in the viscosities of the two polymers, a millefeuille-like microcellular structure was created from a 50/50 blend. Foams with millefeuille-like cellular structures show unique anisotropic mechanical properties, and this study reveals a method for preparing foams of this type.
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