In situ FTIR measurement of carbon dioxide sorption into poly(ethylene terephthalate) at elevated pressures

Knowledge of the sorption rate and solubility of CO2 in polymers are of great importance for developing technologies utilizing high-pressure and supercritical CO2-assisted processes. Many conventional techniques for measuring gas sorption have inherent complications when used at elevated pressures. In this work, we demonstrate the use of near-IR spectroscopy as an accurate method to measure CO2 sorption kinetics and solubility in PET at elevated pressures. Sorption kinetics and solubility are measured at 0, 28, and 50°C between pressures of 57.1 and 175.2 atm. Both initially amorphous and initially partially crystalline samples of PET are studied, and the effects of the initial crystallinity are determined. In addition, the effects of CO2 processing on the final crystallinities of our samples are measured. Crystallization was induced in PET at 28 and 50°C over the range of pressures studied. However, at 0°C, no detectable crystallization occurred in PET, even in the presence of high pressures of CO2. The method demonstrated in this work could easily be extended to directly measure CO2 sorption in other polymers.