Biodegradable Aromatic–Aliphatic Copolyesters Derived from Bis(2-Hydroxyethyl) Terephthalate for Sustainable Flexible Packaging Applications

Bis(2-hydroxyethyl) terephthalate (BHET) is one of the major products in the process of chemical recycling of waste poly(ethylene terephthalate) (PET). In this study, we synthesized a series of biodegradable aromatic–aliphatic random copolymers, poly(ethylene aliphatate-co-terephthalate), directly from BHET together with aliphatic dicarboxylic acids including succinic acid (SA), adipic acid (AA), sebacic acid (Seb), and dodecanedioic acid (DDDA) via a two-step melt polycondensation reaction. The composition of the copolymers was adjusted precisely to optimize their crystallinity, thermo-mechanical properties, and biodegradation performance. In particular, the aromatic–aliphatic copolymer films exhibited excellent elastic properties, displaying tensile strength <27 MPa and elongation at break near 700%, as well as excellent optical transparency (haze <10%), thereby outperforming the conventional petroleum-derived and biodegradable polymers. The biodegradable aromatic–aliphatic copolymers synthesized based on BHET with excellent transparency, mechanical properties, and biodegradability show remarkable potential for open-loop recycling from PET waste and sustainable packaging applications.