Comprehensive modelling strategy for gas transport in polymers: Analysis of swelling and non-swelling agents at high pressures

Gas transport in polymers is a process governed by the interplay between polymeric structure, gas properties, and operating conditions. This work analyzes the solubility and transport properties of different gases in five different industrially relevant polymeric systems, such as Matrimid/P84 polyimide blends, perfluorosulfonic acid membrane (PFSA) Nafion, as well as natural rubber (NR), silicone rubber (PDMS) and a fluorinated rubber (FKM), using a thermodynamic modeling framework, with focus on high-pressure conditions. Specifically, equations of state (EoS) and non-equilibrium thermodynamic for glassy polymers (NET-GP) approaches are able to describe gas solubility, and are combined to the Standard Transport Model (STM) to estimate diffusivity and permeability at various temperatures and pressures, with emphasis on the comparison of swelling and non-swelling penetrants, free-volume variations, and plasticization phenomena. The results obtained reveal the ability of the models to describe the complex experimental behaviors, including challenging systems, such as glassy polymer blends or PFSA membranes. A thorough analysis of the gas transport and sorption properties in the different systems with the penetrant characteristics and with the polymer response to sorption is then performed to elucidate the prevailing effect shaping the behavior of the various systems. Therefore, the model proved to be a powerful tool to inspect the high-pressure induced changes in gas transport, and to predict the solubility and permeability properties in a wide range of conditions.