Enhancing the toughness of poly(lactic acid) with a novel, highly flexible and biodegradable polyester: poly(ethylene adipate-co-terephthalate) terephthalate

As a typical biodegradable material, poly(lactic acid) (PLA) has great development potential in fields such as packaging, textiles and biomedical applications due to its high modulus and strength as well as excellent biocompatibility. However, the inherent brittleness and poor toughness of PLA significantly limit its widespread application. In this study, a biodegradable aliphatic-aromatic copolyester called poly(ethylene adipate-co-terephthalate) (PEAT) was synthesized using the industrially well-established direct esterification method. PEAT demonstrated excellent flexibility and extremely high fracture elongation. Its fracture elongation exceeded 900%, making it a highly ductile material with exceptional toughness. Given the complementary nature of PLA and PEAT, blending PLA with PEAT becomes a natural choice for improving the performance of PLA. The influence of the addition of PEAT on the mechanical properties, thermal performance, crystallization, phase morphology and rheological behavior of the blends was thoroughly investigated. With the addition of PEAT, the fracture mode changed from brittle fracture of the neat PLA to ductile fracture of the blends as illustrated by tensile test. The best toughening effect on PLA was achieved at a PEAT content of 30 wt%, with the elongation at break increasing from 6.7% for neat PLA to 359% for the binary blend, an improvement of 53 times. Additionally, the impact strength also increased from 4.4 kJ/m2 to 10.5 kJ/m2, an increase of 138%. DSC revealed that PEAT had a certain influence on the crystallization behavior of PLA. SEM showed that the PEAT toughening mechanism was primarily attributed to a shear yielding mechanism triggered by debonding cavitation.