Investigation of sorption and diffusion of supercritical carbon dioxide into poly(vinyl chloride)

The interaction of supercritical carbon dioxide (scCO2) with poly(vinyl chloride) (PVC) was systematically investigated. PVC films of 0.5 mm thickness were treated with CO2 at pressures between 5 and 40 MPa, at temperatures between 40 and 70°C and soaking times between 0.5 and 7 h. The gravimetric desorption data were kinetically and thermodynamically evaluated assuming Fickian diffusion and the morphology changes due to the CO2 treatment investigated by microscopic methods. The sorbed amount of CO2, q (q=gCO2/gpolymer) ranged between 0.03 (5 MPa, 70°C) and 0.13 (15 MPa, 40°C). The desorption diffusivities, Dd, were in the order of 0.1×10−11 m2/s and decreased with decreasing amounts of CO2. In contrast, the sorption diffusivities, Ds, were markedly higher and varied between 0.7×10−11 and 2.5×10−11 m2/s (20 MPa, 40–70°C). The CO2 treatment changed the polymer chain structure, macroscopically visualized by the film opaqueness and by the density decrease to 1.05 g/cm3. Microcellular structures were not detected.