Reactive Chain Extension and Nanoclay-Enabled Foaming of High-MFI PBAT for High-Expansion, Compostable Polymer Foams

This work reports a scalable strategy for producing high-expansion, biodegradable, and compostable foams from commercially available high-MFI poly(butylene adipate-co-terephthalate) (PBAT), which is typically unsuitable for foaming due to its low melt strength. Reactive melt chain extension was employed to substantially enhance PBAT viscoelasticity, resulting in a 2348% increase in zero-shear viscosity and a reduction in melt flow index from 449 to 1.86 g/10 min, thereby enabling stable chemical foaming using azodicarbonamide (ADC). FTIR analysis confirmed near-complete decomposition of ADC at the foaming temperature (200 °C). The unfilled PBAT foam exhibited a bimodal closed-cell structure with an average cell diameter of 467 ± 4.95 μm, a foaming ratio of ∼89%, and an expansion ratio of ∼10. To further improve foamability and functional performance, organically modified (Cloisite 20A) and unmodified (Cloisite Ca++) nanoclays were incorporated at loadings of 1–3 wt %. Nanoclay addition enhanced melt strength, promoted crystallization, and increased expansion behavior, with the 3 wt % Cloisite Ca++ formulation achieving a foaming ratio of ∼94% and an expansion ratio of ∼15. This formulation also exhibited improved thermal insulation performance, with a thermal conductivity of 0.293 Wm–1 K–1 at 40 °C. Compostability testing conducted according to ISO 20200 demonstrated complete disintegration of all foam formulations within 60 days, confirming that chain extension and nanoclay incorporation do not hinder biodegradation. Overall, this study establishes an industry-relevant pathway for converting high-MFI PBAT into high-performance, fully compostable foams suitable for sustainable packaging and related applications.