Dynamic Cross-linked Poly(butylene adipate-co-terephthalate) for High-Performance Green Foam

The insufficient molecular weight of linear poly(butylene adipate-co-terephthalate) (PBAT) leads to poor foamability and mechanical performance of foams, which seriously restricts the industrial application of PBAT as foam materials. Herein, biobased itaconic anhydride was grafted onto PBAT backbone, and then epoxidized soybean oil was added to obtain a dynamic cross-linked network based on Zn(II)-catalyzed transesterification. The rheology results showed that the storage modulus and viscosity of the PBAT vitrimers increased obviously, exhibiting a viscous liquid-like to elastic solid-like transition behavior with increasing cross-linked degrees. Reversible cleavage of the cross-links and reformation of the integrated cross-linked network through rebonding of the dynamic bonds were observed under shears of alternative large- and low-amplitude oscillations, endowing PBAT vitrimers with fluidity and elasticity during processing. PBAT vitrimers exhibited strain-hardening behavior in an extensional flow and could be foamed by supercritical carbon dioxide foaming. The lightweight foam could show an expansion ratio of up to 26.7-fold and a density of 0.045 g/cm3. On coupling the cell structure and mechanical properties contributed by the dynamic cross-linked network, the foams showed enhanced elasticity, specific compressive strength, and damping properties. The strategy of altering the viscoelasticity and mechanical properties of PBAT simultaneously by a dynamic cross-linking network provides a new approach toward obtaining high-performance PBAT foams.