Toughening of poly (lactic acid) by poly (β-hydroxybutyrate-co-β-hydroxyvalerate) with high β-hydroxyvalerate content

Fully bio-based and biocompostable poly (lactic acid)/poly (β-hydroxybutyrate-co-β-hydroxyvalerate) (PLA/PHBV) blends were prepared by melt compounding. PHBV with a high β-hydroxyvalerate content (40 mol%) was used in this work. Miscibility between the PLA and the PHBV, phase morphology, thermal behavior, mechanical properties and toughening mechanism of the PLA/PHBV blends were investigated. The blends showed two separate glass transition temperatures, indicating that the PLA and PHBV are not miscible. Transmission electron microscopy (TEM) showed that PHBV changed gradually from a dispersed phase into a continuous matrix up to 50 wt% of the PHBV. At low PHBV content (<20 wt%), the crystallization of fine dispersed PHBV domains was suppressed resulting in rubbery particles in the amorphous PLA matrix due to lack of nuclei. The structure–property study indicates that the ductility and toughness of the PLA can be effectively improved by incorporation of 10–30 wt% of the PHBV, as evidenced by a significant increase in the elongation at break and impact toughness. The local deformation mechanism was well studied by scanning electron microscopy (SEM). It revealed that fibrillation, partial interfacial debonding, PHBV domain cavitation and matrix yielding are involved in the toughening mechanism of the PLA/PHBV blends under impact and tensile testing conditions.