Tailor-made coextruded blown films based on biodegradable blends for hot filling and frozen food packaging

Biodegradable polymers still have severe limitations in their application over wide temperature ranges. In this study, we developed coextruded bilayer biodegradable packaging suitable for either hot-filling and frozen food products. The films were realized by combining an inner layer, made of Ecovio and amorphous poly(lactide) (PLA4060) blend, providing high ductility and sealability, with an outer layer made of poly(butylene succinate) (PBS) and semicrystalline PLA4032 blend, contributing to barrier properties and thermal resistance. The concentration of each blend was optimized for the target application based on preliminary chemical-physical investigations. Then, three bilayer structures with different relative thicknesses of the layers were realized and analyzed for their mechanical, barrier, wettability, sealability and overall migration properties in the −18÷85 °C temperature range, to check their compliance with the needs of food packaging applications involving both thermal treatment and freezing. The coextruded films had functional performance generally intermediate those of the single layers and weighted on their relative thicknesses, and overall migration values complying the limits of Regulation (EU) No 10/2011 for plastic packaging intended for both hot filling process and long-term frozen food storage. Among all, the most suitable structure for the target application was the bilayer film with the largest thickness of the outer layer (i.e. 50 µm), which showed the best balance between stiffness and ductility in the explored temperature range. In particular, it displayed the lowest lowering of elastic modulus at 85 °C, which becomes equal to 135 MPa, and an elongation at break equal to 40 % at −18 °C.