A new study published in Engineering has established a catalyst-free, kinetics-directed strategy for controlled oligomeric depolymerization of polyethylene terephthalate (PET), enabling tailored upcycling into high-performance thermoplastics with improved sustainability and scalability. Researchers from East China University of Science and Technology employed 1,4-cyclohexanedimethanol (CHDM) as both solvent and reagent to drive efficient transesterification under mild conditions, eliminating reliance on external metallic catalysts that often introduce contamination and complicate downstream purification.

The team developed a kinetic model based on population balance equations (PBEs) to precisely regulate the molecular weight distribution (MWD) of PET-derived oligomers, moving beyond conventional models that only track monomer concentration or bulk weight loss. Experimental investigations confirmed that PET depolymerization proceeds mainly through a random chain scission mechanism with an activation energy of 76.08 kJ/mol, while the contribution of chain-end scission remains negligible. By adjusting reaction temperature and duration, the approach yields well-defined oligomers with tunable weight-average molar masses suitable for direct repolymerization.

Structural characterizations using ¹H nuclear magnetic resonance and Fourier-transform infrared spectroscopy verified the incorporation of CHDM into oligomer chains and the progressive cleavage of PET backbones with consistent release of ethylene glycol as a byproduct. Thermal analyses revealed gradual reductions in melting and crystallization temperatures alongside declining crystallinity as depolymerization advanced, consistent with the formation of shorter, more amorphous oligomeric chains.

The resulting oligomers were directly repolymerized without additional esterification or pre-polycondensation steps, simplifying operations and lowering energy consumption while remaining compatible with existing polycondensation infrastructure. The upcycled products include recycled thermoplastic polyester elastomers (rTPEEs) and recycled glycol-modified PET (rPETG), whose mechanical performances match or exceed those of commercial virgin materials.

Validation in a 15 L reactor demonstrated the model’s robustness for scaled-up production, with predicted molecular weight profiles closely matching experimental measurements and high statistical agreement across multiple metrics. This streamlined, catalyst-independent pathway provides molecular-level tunability and industrial scalability, supporting the development of a circular polymer economy by converting PET waste into value-added materials with reduced environmental impact.

The paper “Kinetics-Guided Controlled Oligomeric Depolymerization of PET for Tailored High-Performance Polymer Upcycling,” is authored by Ran Cui, Jie Jiang, Chenyang Li, Man Zhou, Weizhong Zheng, Shicheng Zhao, Ling Zhao, Zhenhao Xi. Full text of the open access paper: https://doi.org/10.1016/j.eng.2026.02.010. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.