Absorption of nitrogen and helium in poly(tetrafluoroethylene)

The absorption of N2, He and two of their mixtures in PTFE are studied up to a maximum pressure of 51 MPa and a temperature range of 0–70°C using a vibrating-reed technique. The data indicate that relatively large amounts of gas are sorbed and that the sorption increases linearly with both the density of the pure gases and the temperature of the polymer matrix. Surprisingly, the amount of sorption is found to be independent of the crystallinity or of the thermal or pressure history of the polymer. The extent of sorption also appears to be independent of the relative concentration of N2 and He in the bulk. Isobaric experiments carried out at 37·9 MPa pressure reveal that the temperature dependence for the solubility of N2 is five times greater than that for He. The corresponding value for the mixture is even higher. A linear extrapolation of the temperature data indicates that the minimum temperatures required for zero absorption of N2 and He in PTFE at 37·9 MPa pressure are 100 K and 10 K respectively.