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Polymeric materials are widely used in every human endeavor (bottles, clothes, containers, toys, tools, etc.) due to their unique properties of chemical and mechanical resistance. They are, however, almost non-biodegradable, and their chemical recycling into monomers is difficult and costly, thereby allowing their accumulation into the environment. This review highlights recent advances in the use of deep eutectic solvents (DESs) as catalysts and/or green solvents in plastics degradation, with the aim of designing greener processes for polymers' chemical recycling, by reusing their monomers. These greener processes, in combination with other catalytic approaches, are aimed at introducing plastics as feedstock into the synthesis of other materials, according to the circular economy principles. [ABSTRACT FROM AUTHOR]

Hydrolytic depolymerization of polyethylene terephthalate (PET) waste was studied using high pressure autoclave reactor at 240 °C (molten state) and autogenous pressure using excess of water in the presence of a phase transfer catalyst polyethylene glycol (PEG 400) and the product profile was traced at various time intervals. In comparison with zinc acetate (used before), PEG 400 was the best catalyst. Concentration profiles were developed for PET, oligomer and terephthalic acid (TPA) using HPLC. Effect of initial molar ratio of 22–110 mol of water/mol PET on depolymerization was studied by using both HPLC and end group analysis. Initial molar ratio of 55–110 mol of water/mol PET was found to give 99 percent conversion in 30 min at 240 °C. A complete conversion of ester linkages to acid group and the desired product TPA was studied. On the basis of ester linkage, 100% conversion was observed in 10–12 min reaction time. At 30 min additional time, it was found to give 95% yield of TPA. Molar concentration of PEG 400 of 2.0 × 10−5 mol/cm3 was sufficient to give the maximum conversion in breaking of ester linkages. The yield and purity of TPA was found to be 90 and 99.1%, respectively. A new mechanism of solid (polymer)-liquid (melt)-liquid (water) phase transfer catalysis (PTC) for hydrolysis was proposed and validated. A pseudo-first order rate equation was fitted for depolymerization with a rate constant of 1.4 min−1 at 240 °C and apparent activation energy of 34.4 kJ/mol. The rate of hydrolysis is very fast and complete depolymerization takes place within 30 min. This is an excellent example of circular economy and cleaner production from waste plastic. [Display omitted] • Conversion of waste PET by hydrolytic depolymerization in to terephthalic acid and ethylene glycol. • Use of PEG 400 as phase transfer catalyst with new mechanism and kinetic model. • A new method of analysis prosed to confirm products. • Hydrolysis rate enhanced and activation energy declined by use of phase transfer catalyst vis-à-vis previous reports/. • Efficient waste polymer recycling as part of circular economy. [ABSTRACT FROM AUTHOR]

Chemical depolymerization of poly(ethylene terephthalate) (PET) waste is a possible remedy to huge amount of solid waste generation as it results in degradation products that possess a potential of recyclability. PET bottle waste was depolymerized by aminolysis using diethanolamine. Novel synthesis of N1, N1,N4,N4-tetrakis (2-hydroxyethyl) terephthalamide (THETA) with 73-76% yield and terephthalic acid (TPA) with 78-82% yield was achieved. The purified products were analyzed by FTIR, melting point, DSC, DTG and1H-NMR. THETA has various applications in the synthesis of rigid polyurethane foam, unsaturated polyester resins and also as a cross linking agent/ hardener for epoxy resins. [ABSTRACT FROM AUTHOR]