Abstract
The gases transport coefficients, permeability, diffusion and solubility, are determined by the time lag method on a specific permeation cell. Three semicrystalline polymers, polyethylene (PE), polyamide 11 (PA11) and poly(vinylidene fluoride) (PVF2), are studied in the presence of helium (He), argon (Ar), nitrogen (N2), methane (CH4) and carbon dioxide (CO2) for temperatures ranging from 40 to 80°C in the case of PE, and from 70 to 130°C for both other materials. The applied pressures are, in the majority of tests, of 10 MPa for He, Ar, N2 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.
Highlights
The gas transport coefficients in semicrystalline polymers are generally complex to determine and to analyse, especially in the field of high pressures and high temperatures
Six semicrystalline polymers were used during this study: a low density polyethylene, noted LDPE, a medium density, noted medium density polyethylene (MDPE), two high density, referenced respectively HDPE and HDPE-Rl, a polyamide 11, noted PA11 and a poly(vinylidene fluoride), noted PVF2
The transport coefficients of five gases, He, Ar, N2, CH4 and CO2, were determined from permeation tests analysed by using the time lag method, for three semicrystalline polymers, PE, PA11 and PVF2, in a range of temperature from 40° to 80°C for PE and from 70° to 130°C for the others
Summary
The gas transport coefficients in semicrystalline polymers are generally complex to determine and to analyse, especially in the field of high pressures and high temperatures. The kind of gas used, characterised by its molecule size or thermodynamical parameters, is a factor influencing these coefficients in the same way as temperature [1, 2]. The equipment of permeation and the time lag method, described in [3], are used to obtain the transport coefficients of gases in three semicrystalline polymers: polyethylene (PE), polyamide 11 (PA11) and poly(vinylidene fluoride) (PVF2). The effects of temperature and of the nature of the gas are discussed and compared with the literature data. In a more specific way, the influence of the plasticizer incorporation in polyamide 11 and the effect of PVF2 processing conditions are shown
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