Degradation of Poly(ethylene terephthalate) Using Metal-Free 1,8-Diazabicyclo[5.4.0]undec-7-ene-Based Deep Eutectic Solvents as Efficient Catalysts

Poly(ethyleneterephthalate) (PET) is glycolyzed to obtain bis(hydroxyethyl)terephthalate (BHET), and repolymerization produces new PET material,making this a sustainable recycling process. However, most studieshave reported common metal-based catalysts, which typically have harshsynthetic conditions and are prone to negative environmental impacts.In this study, 1,8-diazabicyclo[5.4.0]undec-7-ene-based deep eutecticsolvents (DBU-based DESs) effectively degraded PET to obtain BHETdue to their high activity, low price, and accessible production properties.Under the optimized reaction conditions (DES 3.2 wt %, PET/ethyleneglycol (EG) 1:3, 180 & DEG;C, 70 min), PET bottle flakes were completelydegraded, and the yield of BHET achieved 83%. In addition, a possibledegradation mechanism was postulated based on experimental data andcalculations using density functional theory (DFT). The formationof hydrogen bonds between EG and DES and between PET and DES can promoteglycolysis of PET, which in turn could facilitate the attack of hydroxyloxygen in ethylene glycol (EG) on carbonyl carbon in PET.

Automated summary

Poly(ethyleneterephthalate) (PET) is effectively degraded to obtain bis(hydroxyethyl)terephthalate (BHET) using deep eutectic solvents (DESs) based on 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) due to their high activity, low price, and accessible production properties. Under optimized reaction conditions, PET bottle flakes were completely degraded with a BHET yield of 83%. The formation of hydrogen bonds between ethylene glycol (EG) and DES, as well as between PET and DES, promotes glycolysis of PET, facilitating the attack of hydroxyl oxygen in EG on the carbonyl carbon in PET.