Supercritical CO₂‐Assisted Foaming of PBST/PHBH Blends: Mechanisms of Morphological Control and Shrinkage Reduction

Abstract Poly (butylene succinate‐co‐terephthalate) (PBST) foams, produced using supercritical carbon dioxide (scCO 2 ) as a physical blowing agent, exhibit significant shrinkage, with a shrinkage rate as high as 80%, which severely limits their practical applications. Current research on improving the dimensional stability of PBST foams mainly focuses on chain extension or mixed‐gas foaming. However, these methods struggle to balance biodegradability with process controllability. Therefore, developing an efficient modification approach to enhance the dimensional stability of PBST foams is crucial. In this study, PBST is modified by blending with poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBH). By optimizing the PBST/PHBH ratio, saturation temperature, and pressure, the dimensional stability is significantly improved. After introduction to 20% PHBH, the PBST blend microcellular foams have a stable expansion ratio of 35.8, and the shrinkage rate decreased dramatically from 85% to 11.6%. SEM analysis shows that PHBH dispersed uniformly as rigid particles within the foam cell walls, inducing an open‐cell structure that facilitates gas exchange and minimizes internal‐external pressure differences. Rheological and cyclic compression tests indicates that PHBH increases the elastic modulus and rigidity of the foam walls, enhancing dimensional stability and shrinkage resistance. This work offers an innovative and eco‐friendly solution for producing high‐expansion, low‐shrinkage PBST foams with excellent dimensional stability.