HIGH-PRESSURE PERMEATION AND DIFFUSION OF GASES IN POLYMERS OF DIFFERENT STRUCTURES

From classical theory, gas permeation rate through an elastomeric membrane from high pressure to low depends directly on the applied pressure differential. However, at several hundred atmospheres, the elastomer can apparently be consolidated, to reduce permeation rate. As a contrast, swelling also occurs with the passage of time in some cases. Many permeation coefficients have been obtained at these pressures for the permeation at different temperatures of two gases through various polymers, and data rationalized. Use of a device to measure the thickness of the pressurized sample membrane in situ has led to correlation being shown at some temperatures between thickness reductions when pressures are applied, and corresponding decreases in permeation coefficients. For some conditions, these changes take several hours to occur, indicating that the polymer T(g) has been increased by the applied high pressure to become near to the test temperature. It is more likely that the compacted polymer is 'leathery' rather than 'glassy'. When permeating gas and elastomer are chemically compatible, swelling has been observed after the initial compaction, sometimes accompanied by a further reduction in permeation rate.