Multiphase PHA/PBAT/bacterial cellulose/starch biopolymer films: balancing high-temperature stability and controlled compostability.

This study reports the development of cost effective multiphase biodegradable composite films based on polyhydroxyalkanoate (PHA), poly(butylene adipate-co-terephthalate) (PBAT), starch (St), and bacterial cellulose (BC) prepared via melt blending without the use of chemical compatibilizers. FTIR analysis, together with mechanical, thermal, and morphological characterization, suggested the presence of intermolecular hydrogen-bonding interactions that contributed to maintaining the structural integrity of the multiphase system. The incorporation of bacterial cellulose and starch increased the initial stiffness and improved the thermo-mechanical stability of the composites, while the quaternary formulation retained 28.7% of its initial elongation after thermal aging at 100 °C. Composting experiments demonstrated that the hydrophilic biofillers promoted accelerated degradation while maintaining adequate thermo-mechanical performance during service. The degradation behavior was satisfactorily described by a modified first-order kinetic model incorporating a residual mass term, with two apparent kinetic stages characterized by different degradation rates. FTIR analysis before and after composting revealed a substantial reduction in ester related functional groups, consistent with extensive ester-bond hydrolysis during degradation. The observed degradation behavior is consistent with the progressive depletion of more readily hydrolysable polymer fractions during composting, although detailed characterization of the residual degraded materials is required to fully elucidate the degradation pathway. Overall, the developed PHA/PBAT/BC/St composites provide a promising biodegradable material platform with balanced thermo-mechanical performance and controlled compostability for sustainable packaging applications.