Preparation and Properties of Poly(Butylene Adipate‐Co‐Terephthalate) (PBAT)/Poly(3‐Hydroxybutyrate‐Co‐3‐Hydroxyhexanoate) ( PHBHHx ) Composite Foaming Materials

ABSTRACT Poly(butylene adipate‐co‐terephthalate) (PBAT) foams suffer from shrinkage during foaming. Biodegradable poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx) as a reinforcing component with excellent crystallization and mechanical properties was blended with PBAT. Using supercritical CO 2 foaming technology, a series of fully biodegradable PBAT/PHBHHx foams was successfully prepared. The incorporation of PHBHHx exerted a dual reinforcing effect on the blend system: it not only improved the mechanical performance but also accelerated the crystallization rate of the PBAT/PHBHHx composites. Concurrently, the formation of microphase‐separated structures in PBAT/PHBHHx blends creates a favorable microenvironment for cell growth during foaming, and this structural advantage contributes to a higher foam expansion ratio. By leveraging the synergistic effect between accelerated crystallization and improved matrix compatibility, the PBAT/PHBHHx foam with a 75/25 mass ratio exhibited remarkable structural and dimensional stability under a foaming pressure of 14 MPa. Specifically, this foam exhibited a high cell density of 1.58 × 10 7 cells/cm 3 and a uniform cell size distribution ranging from 80 to 140 μm. More importantly, its shrinkage rate was drastically reduced from 60% (observed for neat PBAT foam) to 33%. This study presents an effective strategy for fabricating PBAT foams with anti‐shrinkage properties and superior mechanical performance, providing a novel approach for this field.