Permeability, diffusion and solubility of gases in polyethylene, polyamide 11 and poly(vinylidene fluoride)

The gases transport coefficients, permeability, diffusion and solubility, are determined by the rime lag method on a specific permeation cell. Three semicrystalline polymers, polyethylene (PE), polyamide II (PA11) and poly(vinylidene fluoride) (PVF2), are studied in the presence of helium (He), argon (Ar), nitrogen (N-2), methane (CH4) and carbon dioxide (CO2) for temperatures ranging from 40 degrees to 80 degreesC in the case of PE, and from 70 degrees to 130 degreesC for both other materials. The applied pressures are, in the majority of rests, of 10 MPa for He, Ar, N-2, and CH4, and of 4 MPa for CO2, except in some particular cases where the influence of pressure was studied. In the case of PE, the influence of the volume fraction of the amorphous phase, ranging from 0.21 to 0.70, the influence of temperature and the influence of the nature of the gas on the transport processes are investigated Also, the independence of these phenomena related to pressure and sample thickness, between 0.5 and 6 mm, is shown. For PA11, after determining the influence of temperature and of the nature of the gas used, the effect of the plasticizer incorporation in this polymer was studied. Regarding PVF2, apart the classic parameters that are temperature and the kind of gas used, we compare the coefficients of transport of CH4 and CO2 in PVF2 made up by extrusion or by compression moulding. For each polymer, it is shown that permeability. diffusion and solubility depend on temperature following Arrhenius' laws. It also seems that diffusion is directly related to the gases molecule size and that the solubility coefficient can be linked to the epsilon /K gases parameter. The comparison of the results obtained with the available data in the literature seems satisfactory.