Biodegradable polybutylene adipate terephthalate foams: Investigating sustainability via reprocessing and green solvent

Incorporating reprocessing, recycling, and sustainable processes and materials is essential for a circular economy. Reprocessing and recycling are related since both help minimize wastage and produce a sustainable regenerative economy. However, polymers might undergo degradation depending on the recycling process, reducing their lifespan. In this study, polybutylene adipate terephthalate (PBAT) undergoes repetitive reprocessing under varied temperatures, times, and shear rates to investigate the evolution of mechanical, chemical, and thermal properties. Furthermore, foaming experiments are conducted using supercritical carbon dioxide (scCO₂) on reprocessed samples to examine changes in the properties and morphology of the foam. The significance of reprocessing PBAT is divided into environmental, temperature, and processing effects. Environmental conditions impact the results where no oxidation effects are noticed in the 2-hour test, while 7 days of humidity exposure lead to a tenfold reduction in polymer viscosity. Different processing techniques reduce the molecular weight of PBAT and alter its polydispersity. Specifically, the number average molecular weight (M_n) decreases from an initial 53 to 37 kDa after processes like extrusion or mixing. However, elongation at break and ultimate strength of PBAT remain unchanged after high-shear extrusion processing. Additionally, PBAT foam morphology evolves over 5 cycles, leading to smaller pores and reducing compressive modulus.