Modification of discarded PET molecular chains with methyl lactate endows the material with degradable properties

The intrinsic chemical stability and high crystallinity of discarded polyethylene terephthalate (dPET) render it extremely resistant to natural degradation, posing a critical environmental challenge. Herein, we report a facile phenolic esterification strategy using methyl lactate (DL) to convert dPET into a novel functional polymer (PBGs) that combines high mechanical strength with controlled degradability. The optimal dPET-to-DL ratio of 1:6 g·mL ^− 1 yields the highest compressive strength, attributed to DL-induced chain extension and cross-linking. Comprehensive structural analyses reveal that lactate incorporation disrupts chain regularity, increases amorphous content, and introduces hydrophilic hydroxyl groups, collectively facilitating water penetration and bulk degradation. Accelerated degradation tests demonstrate a distinct three-stage bulk erosion profile (mass losses of 0.22%, 4.12%, and 7.22% over three consecutive 15-day periods), driven by synergistic chain scission, microcrack propagation, and oligomer plasticization. Notably, the modified material retains core thermal stability while exhibiting significantly enhanced degradability compared to pristine dPET. This work presents a viable upcycling strategy that transforms persistent dPET waste into a mechanically robust yet environmentally degradable polymer, contributing to a more sustainable plastic economy.