Equilibrium solubility of CO2 in rubbery EVA over a wide pressure range: effects of carbonyl group content and crystallinity

The equilibrium CO2 sorption isotherms and isobars for rubbery EVA containing various amounts of vinyl acetate (VA) over a wide pressure range 10–340 atm and 25–52 °C were investigated. The normalized CO2 sorption concentration (in cm3 (STP) CO2/mole VA) isotherms of these polymers as a function of pressure consisted of two distinct regions turning at near Pc. The normalized sorption isotherms in these two distinct regions could be fairly described by two respective power laws: C=KaPna for above Pc and C=kbPnb for below Pc. The normalized CO2 sorption isotherms were found to be about the same for four EVA samples having different VA contents for below Pc, suggesting that the sorption process at below Pc may be mainly driven by the presence of carbonyl groups. At above Pc, the degree of crystallinity of the polymer appeared to be a major factor to affect the sorption process, with the higher the degree of crystallinity, the lower the normalized CO2 sorption concentration in the polymer. The sorption isobars of the polymer as a function of temperature were governed by the interplay of density, viscosity, and diffusivity of CO2 depending on the pressure studied.