Transport Properties of Gases in Polymers: Bibliographic Review

After some general considerations and basic equations on transport phenomena in polymers, this review, exclusively bibliographical, presents different concepts and theoretical models that have been proposed and developed to describe the transport mechanism of molecular species in polymers by diffusion. Based on numerous previous studies, it will show how the permeability of gases (or organic vapours) depends strongly on the polymer structure (degree of crystallinity, thermal and mechanical histories), on the penetrant size and nature as well as on the conditions of temperature and pressure

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 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

Transport Properties of Gases in Polymers: Experimental Methods

The permeability of gases in polymers is a property inherent to their structure, which results, firstly, from the absorption of fluids by the material, then, from the diffusion of these products through the polymer matrix. The capacity of a gas to cross more or less fast a material can be used in numerous industrial domains. For example, polymers of low permeability are looked for in domains as different as the oil production, the food packaging or the automotive industry. For oil applications, the main function of polymers is to ensure the leakproof of pipes for example. In that case, materials are in contact of gas at high temperature and high pressure. As the information concerning the gases transport coefficients in these extreme conditions was not available in literature, devices able to give access to these properties were developed. In this paper, the methods for obtaining the transport coefficients and a brief bibliographical review of the various existing experimental techniques are presented. Then, the various experimental devices developed are described in detail

Analyse et simulation de l'influence de la température et de la pression sur les coefficients de transport du CO2 dans du PVDF

Ce travail est consacré à l'optimisation des coefficients de transport de gaz dans les polymères. Il consiste à modéliser l'influence de la température et de la pression sur le coefficient de diffusion. La modélisation est validée par optimisation sur le système CO2-PVDF. Un modèle quadratique en pression généralisant des travaux existants est proposé. Ce modèle décrit en particulier l'effet des hautes pressions sur les coefficients de transport