Evaluation of the thermal-mechanical properties, overall migration, wettability, and freshwater degradation of blends of polyhydroxyalcanoate copolymers

This study explores the effects of blending poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] on the thermomechanical, migration, wettability, and biodegradation behavior of biopolymer films. Blends containing 10–50 wt% commercial P(3HB-co-4HB)/PHBV compound (PX) were processed via twin-screw extrusion and characterized. Dynamic mechanical and rheological analyses revealed phase-separated systems with partial miscibility, where PX acted as a softening phase, thereby reducing stiffness and improving processability. Migration tests under EU 10/2011 conditions revealed that all formulations complied with the limits for aqueous, acidic, and alcoholic simulants; nevertheless, 95% ethanol caused greater migration due to swelling effects. Aging and FTIR analyses indicated that the PHBV-rich blends retained better stability, whereas the PX-rich blends exhibited oxidative degradation and embrittlement. The wettability results demonstrated increased hydrophobicity with increasing PX content, whereas biodegradation in freshwater and sediments confirmed extensive disintegration within 20 weeks, particularly for the PHBV_30PX blend. Overall, the controlled incorporation of P(3HB-co-4HB) allows tuning of the mechanical flexibility, surface properties, and degradation rate, supporting the development of sustainable PHBV-based materials for packaging and biomedical applications.