An Integrated Approach to the Design of PHBV-Based Blends: Structure–Property–Performance Relationships for Compostable Packaging

Environmental concerns with petroleum-based polymers have accelerated the development of biodegradable alternatives, making poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) a promising candidate for sustainable packaging. However, its functional performance necessitates modification through blending. In this study, blends containing 65–85 wt.% polylactide (PLA) were investigated to establish structure–property relationships relevant to compostable packaging. The results reveal partial miscibility of the blends and pronouncedcomposition-dependent changes in morphology and thermal behavior, characterized by an increase in glass transition temperature and a decrease in PLA melting temperature. Increasing PLA content (≥80 wt.%) enhanced thermal stability, increasing the degradation temperature to 288.0 °C. In contrast, higher PHBV content (≥25 wt.%) significantly improved barrier properties of PLA, reducing oxygen and water vapor transmission rates to 74.47 cm3 m−2 day−1 and 29.11 g m−2 day−1, respectively. Biodegradation behavior revealed complete degradation of PHBV after 56 days, whereas PLA showed only 1.29% mass loss under identical conditions. In the blends, biodegradation proceeded preferentially through the PHBV phase, resulting in composition-dependent mass loss. Among the investigated compositions, PLA65/PHBV provided the most balanced combination of barrier performance, mechanical behavior, and biodegradation response. Overall, these findings demonstrate that tailoring composition enables the design of polymer systems for sustainable packaging applications.