Solubility and diffusivity of supercritical CO2 for polycaprolactone in its molten state: Measurement and modeling using PC-SAFT and free volume theory

Abstract

A quantitative understanding of the solubility and diffusivity of CO2 in polycaprolactone (PCL) is crucial for designing PCL manufacturing processes that employ CO2. Both properties were experimentally and theoretically investigated at 373 K to 473 K and up to 20 MPa using the perturbed-chain statistical associating fluid theory (PC-SAFT) and free volume theory. CO2 solubility was found to obey Henry’s law, and PC-SAFT provided correlations of the measured solubilities using the binary interaction parameter, kij, for data fitting to within 1.5% of average relative deviation (ARD). Additionally, the approximated curve of kij as a function of temperature assisted in describing CO2 solubility at other temperatures. The diffusion coefficients of CO2 in PCL were determined using experimental sorption curves and were described using the free volume theory. The model parameters determined using correlations of the diffusion coefficient in PCL could be used to predict CO2 diffusivities in other polymers.