Two mathematical models, Sanchez-Lacombe equation of state and the Perturbed-Chain Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the poly(l-lactide)-CO2 and poly(d,l-lactide-co-glycolide)-CO2 systems. Aspen Polymer Plus software was used. The characteristic parameters for the components and the binary interaction parameters were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both models are reliable in describing the phase equilibrium of the investigated systems.
The solubility of CO2 in saturated polyesters at different temperatures and pressures has been measured using a magnetic suspension balance. The solubility data were used for estimating the binary diffusion coefficients. The results show a good solubility of CO2 in polymers, up to 0.64 g CO2/g polymer. The diffusion coefficients of supercritical CO2 in polymers have generally high values. DSC and XRD analyses of the semi-crystalline polymer samples indicate that amorphous degree of polymers after exposure to CO2 is increased.