Innovative approaches to chemical recycling of polyethylene terephthalate waste: Investigating key components and their emerging applications.

Polyethylene Terephthalate, a widely recognized thermoplastic, is used in numerous sectors including packaging, textiles, electronics, construction, and medical due to its lightweight, cost-efficiency, transparency, flexibility, quick drying, durability and excellent gas/moisture barrier properties. However, its non-biodegradable nature poses significant environmental concerns, necessitating effective recycling and reuse methods. Over the past decades, scientists have focused on both mechanical and chemical recycling methods for PET waste to produce new molecules with potential applications. This review provides a comprehensive account of utilizing PET waste as a feedstock for synthesizing new molecules through various recycling techniques. An up-to-date and comparative overview of different chemical recycling techniques, including ammonolysis, aminolysis, glycolysis, alcoholysis, and hydrolysis in terms of reactants, reaction conditions, products, and yields are outlined. Applications of depolymerized end products like terephthalamide, NN'-bisallyl-terephthalamide, terephthalic dihydrazide, NN'-diphenyl-terephthalamide, dimethyl-terephthalate, dimethyl terephthalate, bis-hydroxyethyl-terephthalate (BHET), bis-hydroxy ethylene terephthalamide (BHETA), terephthalic acid etc. are succinctly presented. These products found potential industrial applications including thermostabilizers, surfactants, hardeners, peptisers, photoinitiators, crosslinkers, plasticizers, adsorbents, sealants, catalysts, etc. Additionally, the conversion of these depolymerized end products into other useful compounds like terephthalonitrile, para-xylylenediamine, 1,4-bis(aminomethyl)cyclohexane, lanthanum complexes, acrylates, BHET and BHETA derivatives, oxadiazole derivatives, 2,2'-(1,4-phenylene)-bis(2-oxazoline), 1,4-cyclohexanedimethanol, dyes, dioctyl terephthalate, butylene-adipate-co-terephthalate, terephthaloyl dichloride etc. has also been detailed along with their potential applications.