Progressing Ultragreen, Energy-Efficient Biobased Depolymerization of Poly(ethylene terephthalate) via Microwave-Assisted Green Deep Eutectic Solvent and Enzymatic Treatment

Abstract

Effective interfacing of energy-efficient and biobased technologies presents an all-green route to achieving continuous circular production, utilization, and reproduction of plastics. Here, we show combined ultragreen chemical and biocatalytic depolymerization of polyethylene terephthalate (PET) using deep eutectic solvent (DES)-based low-energy microwave (MW) treatment followed by enzymatic hydrolysis. DESs are emerging as attractive sustainable catalysts due to their low toxicity, biodegradability, and unique biological compatibility. A green DES with triplet composition of choline chloride, glycerol, and urea was selected for PET depolymerization under MW irradiation without the use of additional depolymerization agents. Treatment conditions were studied using Box-Behnken design (BBD) with respect to MW irradiation time, MW power, and volume of DES. Under the optimized conditions of 20 mL DES volume, 260 W MW power, and 3 min MW time, a significant increase in the carbonyl index and PET percentage weight loss was observed. The combined MW-assisted DES depolymerization and enzymatic hydrolysis of the treated PET residue using LCC variant ICCG resulted in a total monomer conversion of ≈16% (w/w) in the form of terephthalic acid, mono-(2-hydroxyethyl) terephthalate, and bis-(2-hydroxyethyl) terephthalate. Such high monomer conversion in comparison to enzymatically hydrolyzed virgin PET (1.56% (w/w)) could be attributed to the recognized depolymerization effect of the selected DES MW treatment process. Hence, MW-assisted DES technology proved itself as an efficient process for boosting the biodepolymerization of PET in an ultrafast and eco-friendly manner.

Natural deep eutectic solvents as thermostabilizer for Humicola insolens cutinase

“…This would imply as a future step, the evaluation of other HBD molecules by docking analysis, targeting different regions of the protein. On the other hand, the observed thermostabilization in NADES solution would be beneficial in exploiting cutinase reaction towards difficult to solubilize substrates and/or in innovative applications such as PET-depolymerization [40].…”

Use of Deep Eutectic Solvents in Plastic Depolymerization

“…The modification of PET particle morphology and crystallinity by DES/MW pretreatment also allowed a better action of leaf-branched compost cutinase (LCCv) in chemo-enzymatic hydrolysis investigated by the same group [49].…”

Degradation by Electron Beam Irradiation of Some Elastomeric Composites Sulphur Vulcanized

“…Biodegradation is carried out in the presence of specific microorganisms, and photodegradation is carried out by means of solar UV radiation and UV irradiation [ 12 ]; both methods are non-polluting but long-lasting. The use of microwaves is also described as a devulcanization treatment [ 13 , 14 ]. Therefore, all degradation methods require an input of external energy of a chemical, thermal, photochemical, or biological nature.…”