Green preparation of biodegradable poly (butylene adipate-co-terephthalate) foam modified with bio-based epoxidized cardanol using supercritical fluid foaming

Poly (butylene adipate-co-terephthalate) (PBAT) foam is a potential alternative to conventional packaging materials. However, its wide adoption is hindered by issues such as low foaming–expansion ratios and shrinkage. A series of biodegradable epoxidized cardanol (EC)-modified PBAT foams were prepared using supercritical carbon dioxide (CO₂) foaming. The addition of EC enhanced the crystallisation temperature and stiffness, and improved the rheological properties, thereby promoting polymer foamability. When the EC content reached 0.6 wt%, lightweight foams with the highest initial expansion ratio (R_v) of 48.4 were produced before shrinkage. N₂ was introduced as a co-blowing agent to reduce shrinkage of the PBAT foams, resulting in the production of a microcellular foam with a stable R_v of 12.9. EC improved the foamability of PBAT while also introducing the co-blowing agent N₂ to resist shrinkage. These findings can serve as valuable insights for the large-scale production of lightweight biodegradable foams.