Depolymerization of waste polybutylene terephthalate in hot compressed water in a fused silica capillary reactor and an autoclave reactor: monomer phase behavior, stability, and mechanism

Depolymerization is a potentially viable means of recycling waste polymers, converting them back into monomers or other useful compounds. Terephthalic acid (TPA) and 1,4-butanediol (1,4-BD) are the depolymerization monomer products of polybutylene terephthalate. Their yields from depolymerization in hot compressed water (HCW) were previously found to be lower than reported theoretical values. Thus, the phase behavior, stability, and mechanism of monomers in HCW were investigated in a fused silica capillary reactor (FSCR) and a stainless steel autoclave reactor. Phase change observations showed that TPA was completely dissolved in water at 300[degrees]C, was relatively stable at 320 to 350[degrees]C, and that its recovery significantly decreased at temperatures above 350[degrees]C. The decomposition of TPA increased with increasing heating time. However, the recovery of 1,4-BD decreased rapidly with increasing temperature or heating time. A mechanism for the stability of TPA and 1,4-BD is proposed based on their depolymerization products. The products were quantified by Fourier transform-infrared spectroscopy, high-performance liquid chromatography, and gas chromatography coupled with mass spectrometry. The wall effect of the stainless steel autoclave promoted the decomposition of TPA and 1,4-BD in HCW. POLYM. ENG. SCI., 57:544-549, 2017. [C] 2016 Society of Plastics Engineers
INTRODUCTION Polybutylene terephthalate (PBT) is an important engineering thermoplastic in automotive and electrical applications. It exhibits favorable electrical and mechanical properties, including thermal stability, low moisture absorption, good solvent resistance, [...]