Biocatalytic depolymerization of waste polyester mooring lines from oil and gas offshore platforms made of poly(ethylene terephthalate) (PET)

BACKGROUND The global concern of plastic pollution in the environment has consistently been emerging in the past years. As one of the main polymers constituting single-use products, poly(ethylene terephthalate) (PET) is found in a plethora of packages for diverse sectors, and its recycling has been broadly addressed. However, other relevant industrial PET wastes have not been under investigation for recycling purposes, such as the polyester mooring lines (PMLs) used to anchor offshore oil and gas floating platforms. In this study, the fibers from either new or used PMLs were characterized according to different techniques (differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance and scanning electron microscopy-energy-dispersive X-ray spectroscopy), which allowed the interpretation of their chemical and thermal properties. The fibers were then used in depolymerization reactions under the catalysis of the cutinase enzyme from Humicola insolens and under different process conditions (fiber length, buffer composition, enzyme dosage, temperature, pH). RESULTS Characterization of PMLs revealed inorganic incrustation in the external fibers, and very similar crystallinity degrees. The molecular weight, on the other hand, was found to be lower in new mooring lines (27 489 g mol(-1)) as compared to used mooring lines (35 813-36 785 g mol(-1)). Throughout depolymerization reactions, a total concentration increase of terephthalic acid of up to 7.4 times (2593 mu mol L-1) was achieved. CONCLUSION The results proved the concept that the studied cutinase can act on PET chains. To the best of our knowledge, this is the first report to describe an enzyme-catalyzed depolymerization of PET from mooring lines, and the results add relevant knowledge for a circular economy of plastic products.