A dynamic system has been developed for measuring permeability and diffusion coefficients for the transport of gases and vapours through polymer films. Activation energies determined for the permeation of methane through low density PE film using this system were found to agree well with values from the literature. The permeation of tetrachloroethylene, nitroethane, dichloromethane and methane through poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film was investigated over the temperature range 20 - 100 °C. Linear Arrhenius plots were found for permeability and diffusion coefficients with a change in gradient and therefore activation energies for permeation and diffusion below the glass transition temperature. This effect was more pronounced for the larger permeant molecules. Permeability and diffusion coefficients were also measured for nitroethane and dichloromethane permeation through poly (ethylene terephthalate) over the temperature range 60 - 140 °C. Once again linear Arrhenius plots were found with a change in gradient at the glass transition temperature. Differences were found between the activation energies for permeation and diffusion of methane in samples of FEP that were annealed at different temperatures, namely 100 °C and 200 °C. Measurements using several techniques showed that the polymer annealed at the higher temperature had greater levels of crystallinity. Sorption isotherms were obtained for dichloromethane uptake in FEP samples in the as-received state, annealed at 100 °C and annealed at 200 °C. The isotherms were all found to show a downward curvature indicative of a dual-mode type sorption. The isotherms obtained with FEP in the as-received state and annealed at 100 °C were very similar whereas the uptake of dichloromethane by the sample annealed at 200 °C was significantly lower. Isotherms obtained for the sorption of nitroethane and tetrachloroethylene showed very little dual-mode characteristics. Solubility coefficients for dichloromethane, nitroethane and tetrachloroethylene sorption in FEP at 30 °C were obtained from static measurements. These were compared with values obtained from the dynamic method and found to be in reasonable agreement. Much larger solubilities were found for tetrachloroethylene than nitroethane despite the two permeants having similar vapour pressures at the measurement temperatures.
|Date of Award||1983|