Synergistic chemo-enzymatic hydrolysis of poly(ethylene terephthalate) from textile waste

Due 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 in order 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 (1,632 cm-1) of TA into the deprotonated state (1,604 and 1,398 cm-1) was observed and bands at 1,728 and 1,398 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 by using the Humicola insolens cutinase (HiC) yielding 97% pure TA, therefore comparable with the commercial synthesis grade TA (98%).