Designing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) films with tailored mechanical properties

Increasing the 3HV molar fraction up to 45 mol% in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HBco-3HV)) monomeric composition is assumed to improve the ductility of P(3HB-co-3HV)-based materials. The objective of the paper was to assess how the polymer recovery treatment and the melt processing temperature could counterbalance this effect. For that purpose, copolymers with different 3HV contents (18, 28 and 40 mol%) and recovered both using a solvent free high-pressure homogenization (HPH) based treatment and a chloroformbased treatment were used to produce non-formulated and self-supported films by thermopressing. The improvement of ductility with increased 3HV content was confirmed whatever the recovery treatment. Lower elongation at break values were obtained for HHP-based extracted copoplymers, due to the presence of impurities, including non-PHAs cell mass, that favored thermal degradation during the film shaping process. An indepth study by differential scanning calorimetry (DSC) analysis of the melt crystallization behavior, coupled to observations in polarized optical microscopy (POM), allowed to predict the optimal processing temperature, i. e. the temperature allowing the formation of microstructures in favor of improved ductility. Tensile properties were discussed in relation to the thermal properties and crystalline structure of copolymers evaluated by wideangle and small-angle X-ray scattering analyses (WAXS/SAXS).