Dissolution-Precipitation Using Natural Terpenes as Pretreatment for PET Enzymatic Depolymerization

Plastics are widely used in short-lived applications but pose a significant environmental challenge, emphasizing the need for efficient recycling strategies. Poly-(ethylene terephthalate) (PET) remains a major focus of these efforts, yet its high crystallinity continues to hinder recycling efficiency across mechanical, chemical, and enzymatic routes. Enzymatic depolymerization offers a sustainable pathway for monomer recovery due to its mild operating conditions and simplified downstream processing. This study reports a green pretreatment strategy for PET using a thymol:carvacrol (1:1) mixture through dissolution-precipitation. A full factorial design was employed to evaluate the influence of dissolution temperature, polymer concentration, and solvent removal rate on crystallinity reduction. Although none of the factors were individually significant within the tested ranges, all treatments reduced PET crystallinity by up to 14.1% without altering the chemical structure of the polymer. Pretreated samples exhibited markedly enhanced enzymatic depolymerization, producing approximately seven times more monomers than untreated PET after 72 h using HiC. These results demonstrate that this natural solvent-based pretreatment effectively lowers crystallinity and substantially improves enzymatic hydrolysis. The approach provides a promising route to enable more efficient PET upcycling and supports the development of greener, more sustainable recycling technologies.