Sorption and diffusion of supercritical carbon dioxide in polycarbonate

Sorption and diffusion of supercritical carbon dioxide (SCCO2) in polycarbonate (PC) at temperatures ranged from 40 to 60 °C and pressures ranged from 10 to 40 MPa are presented in this study. The equilibrium CO2 sorption in PC specimen with 0.5 mm thickness has been observed at 2 h, and the experimental data were analyzed by a mass-loss analysis. The linear relationship between mass gain and square root of time indicates that SCCO2 conducted Fickian sorption and desorption in the PC specimen within the experimental conditions. The equilibrium CO2 sorption amount in PC specimen varies from 7.6 wt.% (at 60 °C and 10 MPa) to 14.7 wt.% (at 40 °C and 40 MPa). Upon plotting the equilibrium sorption amounts against SCCO2 density, crossover of the sorption isotherms is observed and the change of mass transfer mechanism is suggested. The sorption diffusivities under supercritical conditions as well as the desorption diffusivities under ambient temperature and pressure were determined. The sorption diffusivities increased with temperature and decreased with pressure of SCCO2, unless the glass transition state of polymer was exceeded. The desorption diffusivities were also observed to increase with CO2 concentration inside the PC specimen. At lower temperature and pressure, the desorption diffusivity may become larger than that of sorption due to the plasticizing effect.