Effect of pressure on CO2 transport in poly(ethylene terephthalate)

Abstract : The CO2 solubility, permeability and diffusion time lag in poly(ethylene terephthalate) are reported at 35 C and 65 C for CO2 pressures ranging from 0.07 atm to 20 atm. The subatmospheric time lag and permeability measurements were made with a glass system at North Carolina State University while the measurements, using an identical polymer sample, between 1 and 20 atmospheres were made at The University of Texas with a metal system capable of tolerating gage pressures up to 30 atmospheres. The measured solubility, permeability and time lag all show strong deviations from the well-known simple expressions for gases in rubbery polymers. The solubility isotherm is nonlinear in pressure and both theta and P are quite pressure dependent with each showing tendencies to approach low and high pressure asymptotic limits. These effects decrease as temperature increases and would be expected to disappear at or near the glass transition where the amorphous regions become rubbery. The importance of reporting the pressure levels used in transport measurements is emphasized for gas/glassy polymer systems where transport process do not follow linear laws. (Author)