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SummaryDue to the rising global environment protection awareness, recycling strategies that comply with the circular economy principles are needed. Polyesters are among the most used materials in the textile industry; therefore, achieving a complete poly(ethylene terephthalate) (PET) hydrolysis in an environmentally friendly way is a current challenge. In this work, a chemo‐enzymatic treatment was developed to recover the PET building blocks, namely terephthalic acid (TA) and ethylene glycol. To monitor the monomer and oligomer content in solid samples, a Fourier‐transformed Raman method was successfully developed. A shift of the free carboxylic groups (1632 cm−1) of TA into the deprotonated state (1604 and 1398 cm−1) was observed and bands at 1728 and 1398 cm−1 were used to assess purity of TA after the chemo‐enzymatic PET hydrolysis. The chemical treatment, performed under neutral conditions (T = 250 °C, P = 40 bar), led to conversion of PET into 85% TA and small oligomers. The latter were hydrolysed in a second step using the Humicola insolens cutinase (HiC) yielding 97% pure TA, therefore comparable with the commercial synthesis‐grade TA (98%).

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A new circular economy concept is presented for the textile sector to convert unwearable polyester textile waste into valuable chemical feedstock. The idea behind it is to develop a new circular economy concept for the most used material in the textile industry, that is, polyester. Hydrothermal hydrolysis, an environmentally friendly process, has been studied for recovering polyester monomeric units. Under high-temperature and high-pressure conditions complete chemical depolymerization of pure poly(ethylene terephthalate) (PET) to terephthalic acid (TPA) was achieved at high yield. The produced TPA was characterized by potentiometric titrations, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and elemental analysis. A series of experiments were performed on the PET material with different intrinsic viscosities to define the appropriate depolymerization conditions related to the temperature ( T), time ( t) and PET:H2O ratio, which enables total conversion of the polymer. Maximal conversion (92%) to TPA was defined at 250℃, pressure of 39–40 bar, PET:water ratio of 1:10 and hydrolysis time of 30 min after reaching steady-state conditions in the reactor. The applied depolymerization route resulted in moderate purity of the originated TPA, which was applied successfully in a laboratory-scale two-step re-polymerization to produce PET resins.