Tests of a “free‐volume” model of gas permeation through polymer membranes. I. Pure CO₂, CH₄, C₂H₄, and C₃H₈ in polyethylene

Permeability coefficients have been measured for CO 2 , CH 4 , C 2 H 4 , and C 3 H 8 in polyethylene membranes at temperatures of 5, 20, and 35°C and at applied gas pressures of up to 30 atm. The temperature and pressure dependence of the permeability coefficients was represented satisfactorily by an extension of Fujita's free‐volume model of diffusion of small molecules in polymers. The results of the present steady‐state permeability measurements provide further support for the conclusion reached from previous unsteady‐state diffusivity measurements that Fujita's model is applicable to the transport of small molecules, such as CO 2 , CH 4 , C 2 H 4 , and C 3 H 8 , in polyethylene. It was previously thought that this model is applicable only to the transport of larger molecules, such as of organic vapors, in polymers.