Application of Magnetic Resonance Imaging to the Investigation of the Diffusivity of 1,1,1,2-Tetrafluorethane in Two Polymers

Abstract

In order to evaluate the suitability of a polymer as a sealing material for certain working fluids used in process plants, information about the fluid diffusivity into the polymer or the polymer permeability to the fluid is a prerequisite. The fluid of interest in the present work is 1,1,1,2-tetrafluorethane, CH₂FCF₃, a partly fluorinated hydrocarbon (HFC) commonly known as refrigerant R134a. HFCs are increasingly used in refrigeration, air conditioning, and heat pump applications as substitutes for the chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs) that are believed to be responsible for ozone depletion in the stratosphere. The polymers studied were FPM, a perfluoroelastomer, and EPDM, an ethylenepropylene-diene rubber. The study was carried out using magnetic resonance imaging (MRI). The contact time dependence of diffusion of the fluid into the polymer, as well as the spatial distributions of spin–lattice, T₁, and spin–spin, T₂, relaxation times, were used as indicators of the influence of the EPDM matrix on the mobility of R134a molecules.