Study on the effects of TPU, PBS, and PPC on the microstructure and supercritical foaming behavior of PBAT blend systems

Supercritical foaming of poly(butylene adipate-co-terephthalate) (PBAT) is governed by its crystallization kinetics and melt rheology, which is essential for the design of biodegradable polyester foams. However, systematic investigations on how co-components with distinct crystalline structures modulate PBAT crystallization, and how these changes impact melt rheology and foaming performance, are still lacking. To address this gap, PBAT-based blend foams with thermoplastic polyurethane (TPU), poly(butylene succinate) (PBS), and poly(propylene carbonate) (PPC) were prepared and analyzed using DSC, rheology, and foam characterization. The results show that at low additive contents, semi-crystalline TPU and PBS, as well as amorphous PPC, promote PBAT crystallization by providing heterogeneous nucleation sites, thereby enhancing bubble formation. However, the effect is modulated by the intrinsic properties of the additives. At higher contents, TPU and PBS progressively form independent crystalline phases, and foaming behavior becomes increasingly governed by their own characteristics: TPU crystalline domains restrict bubble growth, while PBS independent crystals reduce foam stability. PPC remains amorphous, but its plasticizing effect lowers melt viscosity, inhibiting foam expansion and narrowing the foaming window. Overall, PBAT foaming is governed by competition between additive crystalline structure and content-induced phase evolution, providing a basis for designing biodegradable foams with balanced expansion, structure, and mechanical properties.