A novel approach for determining the proportions of pyrolysis and hydrolysis in the degradation of poly(ethylene terephthalate) in ¹⁸O-labeled steam

The proportions of pyrolysis and hydrolysis in poly(ethylene terephthalate) (PET) degradation were determined from the decomposition of PET in ¹⁸O-labeled steam, producing labeled and unlabeled terephthalic acid. At a 100 vol % steam concentration at 400 °C, 74% of the ester bonds were pyrolyzed and 26% were hydrolyzed, as determined by gas chromatographymass spectrometry. In addition, thermogravimetric analysis revealed the activation energy to be 199 kJ mol^-1 under pyrolytic conditions, decreasing with increasing steam concentration, and reaching a minimum of 132kJmol^-1 at 75vol %.