Abstract
An effective process for synthesizing liquid dihydroxyl group-ended oligomers directly from waste polyethylene terephthalate (PET) using a metal chelating agent, ethylenediaminetetraacetic acid (EDTA), is described in this study. The deactivation of transesterification catalyst was confirmed by a model process that involves the reaction of bis(2-hydroxyethyl) terephthalate with diethylene glycol under different catalytic conditions. The depolymerization of PET was performed with an excess amount of diethylene glycol and Zn2+ catalysts to form intermediates. The chelating agent was then introduced as a catalytic defunctionalizer, after which the residual glycols were distilled and recovered under reduced pressure. The obtained polyols were characterized by 1H and 13C nuclear magnetic resonance, gel permeation chromatography, and viscometry. Utilizing EDTA showed high efficiency in blocking catalysts during high-temperature distillation, resulting in maximum trimer chain-length sized and low-viscosity liquid polyols. Subsequently, thermoplastic polyurethanes (TPUs) were prepared using synthesized polyols as the soft segment, with 4,4’-methylene-bis(phenyl isocyanate) and 1,4-butanediol as the isocyanate and chain extender, respectively. The final TPUs were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, and mechanical testing.
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