Morphology and Properties of Injection Molded Solid and Microcellular Polylactic Acid/Polyhydroxybutyrate-Valerate (PLA/PHBV) Blends

Blending poly(lactic acid) (PLA) with polyhydroxybutyrate-valerate (PHBV) presents a practical approach to producing fully biobased blends with tailored material properties and improved foam morphologies. This study investigated the effects of the PLA/PHBV blend composition on the morphology, as well as the thermal and mechanical properties, of both solid and microcellular PLA/PHBV injection molded components. Nitrogen (N-2) in the supercritical state was used as the physical blowing agent for the microcellular injection molding experiments. Thermal analysis results showed no difference in the thermal properties of solid and microcellular injection molded specimens. It was also found that the T-g of the PLA phase in the PLA/PHBV blends decreased with increasing PHBV content for both solid and microcellular specimens. In addition, PHBV content exceeding 45% significantly increased the crystallinity of PHBV in the PLA/PHBV blends and improved the storage modulus of both solid and microcellular components. PLA/PHBV blends were immiscible when the content of PHBV exceeded 30%; PLA/PHBV blends were only miscible with a low weight ratio of PHBV. The increase of PHBV content significantly decreased the cell size and increased the cell density in the microcellular specimens and resulted in some interesting bimodal microcellular structures within the PLA/PHBV (70:30) blend. Additionally, adding PHBV decreased the tensile strength slightly for both solid and microcellular specimens. Furthermore, adding PHBV did not cause any significant changes in the modulus of the solid or microcellular specimens.