Modeling the thermodynamic behavior of poly(lactide-co-glycolide) + supercritical fluid mixtures with equations of state

In this work, the thermodynamic behavior of binary systems composed by one commercial biodegradable copolymer [poly(d,l-lactide-co-glycolide)] and supercritical fluids, SCF, (dimethyl ether, carbon dioxide, chlorodifluoromethane and trifluoromethane) was studied. The perturbed chain-SAFT (PC-SAFT) and the Sanchez–Lacombe (SL) non-cubic equations of state (EoS) were used to model the fluid–liquid equilibrium (FLE) for these binary systems, by fitting one temperature-dependent binary interaction parameter. For comparison, the same data were also modeled by using the traditional Peng–Robinson (PR) cubic EoS. The three PC-SAFT and SL pure-component parameters and two PR pure-component parameters were regressed by fitting pure-component data (liquid pressure–volume–temperature, PVT, data for copolymer and saturated liquid vapor pressure and molar volume for SCF). Liquid PVT data of PLAG copolymers were estimated by using a group contribution method, taken from literature. The estimation of pure-component and binary interaction parameters was performed by using the modified maximum likelihood method with an objective function that includes the cloud point pressure. An excellent agreement was obtained with the PC-SAFT EoS, while the performance of the SL and PR EoS were less satisfactory.