Abstract
The main objective of this study is to assess the validity of a free-volume model of gas permeation through rubbery polymer membranes. Such information is of importance for the development of new membrane processes for the separation of gas mixtures. Steady-state permeability coefficients for N/sub 2/O in polyethylene between 20 and 50/sup 0/C and at pressures up to 15 atm were found to be 45% higher (on the average) than values predicted by the free-volume model. The difference between the experimental and theoretical permeability coefficients for N/sub 2/O is about twice as large as observed with many other gases in polyethylene. Permeability, diffusion time-lags, and absorption measurements were made with n-C/sub 4/H/sub 10/ in poly(eta-butyl methacrylate) at 30/sup 0/C and subatmospheric pressures. The experimental time-lags agreed satisfactorily with values predicted by the free-volume model, using model parameters obtained from gas absorption measurements. However, the experimental permeability coefficients were substantially higher than the theoretical values. This may be due to a non-Fickian transport component because the measurements were made at only 3/sup 0/C above the glass transition temperature of the polymer. This study was recently extended to the solution and transport of gases and vapors in glassy polymers. Satisfactory agreement betweenmore » experiment and theory was found for the solution, permeation, and diffusion of acetone, benzene, and methanol in ethyl cellulose and water vapor in poly(acrylonitrile) and for the solution of vinyl chloride monomer in poly(vinyl chloride). A generalized model of transport of small molecules in polymers has been developed. The model incorporates free-volume and dual-mode sorption concepts, and should be applicable both to rubbery and glassy polymers.« less
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