(384e) Modeling Sorption Kinetics of Carbon Dioxide in Initially Glassy Polymers Using Non-Equilibrium Thermodynamics

Carbon dioxide in its liquid and supercritical state is a very attractive replacement for traditional aqueous and organic solvents in a number of industrial applications of polymeric materials, primarily due to its tunable solvent properties, low cost, low toxicity, non-flammability, and because it is an excellent plasticizing agent for many polymers. In most of its potential applications a key element for success in controlling final product quality relies on the ability to correctly predict sorption kinetics, as well as pertinent dilation of the polymeric matrix, at different temperatures and pressures. Indeed, a reliable thermodynamic model, capable of describing swelling of glassy polymers starting from dry polymeric matrices up to fully plasticized materials, is an essential pre-requisite for any transport model aimed at predicting concentration profiles as well as sorption, desorption and even dissolution kinetics of polymeric films. In the present work, solubility and swelling isotherms have been measured at two different temperatures and over a wide range of pressures using high-pressure Ellipsometry and high-pressure QCM and successfully modeled with NET-GP approach modified for high pressures. Differential sorption experiments have been also performed on the same system using high-pressure QCM in order to test the one-dimensional transport model for sorption and dilation kinetics developed coupling non-equilibrium thermodynamic model to free volume theory for diffusion and a simple rheological equation for volume relaxation. Throughout the range of pressures studied, from gas to supercritical fluid, the model has been able to correctly represent sorption and desorption cycles, in the rubbery as well as in glassy state by means of the use of only one adjustable parameter, which ultimately refers to the bulk viscosity of the polymeric species in glassy states.