A comprehensive theoretical framework for the sub and supercritical sorption and transport of CO₂ in polymers

The sorption and transport of CO₂ in two polymers, Matrimid and PDMS, were modelled using data available across the critical region, at various temperatures and up to 18 MPa. The experimental trends show a complex behavior that is affected by the transition from gas-like to liquid-like density of CO₂, as well as by the sorption-induced glass transition of the polymer. The Non Equilibrium Thermodynamics (NET-GP) approach for the solubility, coupled to its complementary tool for the permeability, the Standard Transport Model (STM), allows to represent thoroughly the complexity of CO₂ sorption and permeation in this operative range with a self-consistent set of parameters. Furthermore, the model offers a deep insight in the swelling induced by CO₂ in the different states of the polymers, and allows to decouple the kinetic and thermodynamic contributions to the transport phenomena in a meaningful way. This work takes a step forward in the understanding and simulation of the complex interactions between high pressure, supercritical CO₂ and industrially relevant polymeric materials.