PBAT-Based Biodegradable Foams as Lightweight Alternatives to Expanded Polystyrene: Effect of Blend Composition on Rheology, Foaming Behavior and Cellular Morphology

Growing environmental concerns and the need to replace fossil-based plastics have accelerated the development of biodegradable foamed materials for lightweight packaging. However, the limited melt strength and poor foamability of biodegradable polymers remain major challenges. This work proposes and systematically investigates novel multiphase biodegradable blend compositions based on PBAT, PLA, PBSA, and thermoplastic starch (TPS), specifically engineered to exploit the complementary properties of each component and improve foamability without compromising processability. The formulations were compounded by co-rotating twin-screw extrusion, processed into films by cast extrusion, and foamed using nitrogen as the blowing agent. Rheological, thermal, mechanical, and morphological characterizations were performed to evaluate the effect of polymer composition. F2 exhibited the highest melt flow rate (5.42 ± 0.10 g/10 min), whereas F1 showed superior melt stability and ductility. Foaming experiments revealed that blend composition significantly affected the cellular structure. F1 produced the most homogeneous cellular structure, exhibiting the highest cell circularity (0.826 ± 0.04). Independent density measurements also showed that F1 exhibited the lowest foam density (0.786 ± 0.02 g/cm3), whereas the TPS-containing formulation (F3) exhibited greater cell coalescence and partial cell collapse. The findings demonstrate that tailoring biodegradable blend composition, in combination with nucleating and chain-extending masterbatches, is an effective strategy to control foam morphology and enhance processing performance. The proposed formulation represents a promising alternative to expanded polystyrene for sustainable lightweight packaging applications.