ATR-IR spectroscopy of superheated water and in situ study of the hydrothermal decomposition of poly(ethylene terephthalate)

Opportunities exist to exploit the unique properties of superheated or near-critical water in the recycling of polymers. Exposure of polyethylene terephthalate (PET) to hot water at 180 °C and 1.0 MPa has resulted in the decomposition of PET and the formation of terephthalic acid. This process was followed, for the first time, via in situ ATR-IR spectroscopy. The high-temperature ATR-IR (attenuated total reflection infrared) approach allows the measurement of IR spectra of polymers subjected to superheated, near-critical or supercritical water. The ATR-IR spectra of liquid water in the temperature range 25–300 °C have also been measured, and evidence of the reduction in the degree of hydrogen bonding in water under these conditions has been obtained. Good potential exists to apply the approach developed here to study processes in near-critical water.