Investigation of Multicomponent Sorption in Polymers from Fluid Mixtures at Supercritical Conditions: The case of the Carbon Dioxide/Vinylidenefluoride/Poly(vinylidenefluoride) System

The simultaneous sorption of carbon dioxide and vinylidene fluoride (VDF) in poly(vinylidenefluoride) from their supercritical (sc) mixtures was studied using an experimental method, already described in a previous publication, based on the gas-chromatographic determination of the equilibrium composition of the fluid phase in contact with the polymer. Argon was added to the system as a nonabsorbable molecular probe in the polymer to take into account the effect of the volume swelling on the measurement. Sorption behavior has been studied at 50 \ub0C by changing the composition and the density of the supercritical phase. We have found that VDF dissolves in its polymer with concentrations much lower than carbon dioxide at similar total and partial pressures. The mixed fluid CO2/VDF behaves as a worse solvent toward PVDF with respect to pure CO2, leading to a reduction of the cumulative sorption. This effect becomes progressively more significant when the fluoromonomer concentration increases. Experimental data obtained from binary systems were fitted using the Sanchez-Lacombe equation of state, and this model was used to estimate the drift in the composition of the polymer phase during the polymerization of VDF in scCO2. This estimate shows that the concentration of the monomer dissolved in the polymer remains low during the whole polymerization