M. Labbé

Diffusion of water through various polymer films: a new high performance method of characterization

Abstract Diffusion of water in polymer films has been characterized by using a new high performance and reproducible method based on permeation measurements. With this method, which uses a fast response water-specific sensor based on dew point measurement, it is possible to determine, from the transient step, the time lag water diffusion coefficient D L and, when the steady state is reached, a mean water permeability coefficient P . In this work we have emphasized the water concentration dependence of diffusion coefficient D . After calibration, the technique yields accurate values of P , consistent with literature data. By testing various polymers, different behaviours with respect to water have been observed, particularly with low density polyethylene (LDPE) which shows significant hydrophobic properties.

Study of transport of small molecules through ethylene-co-vinyl acetate copolymers films. Part A: Water molecules

Abstract The transport of liquid water through poly(ethylene-co-vinyl acetate) (EVA) films with 4.5%, 19%, 33%, 50% and 70% w/w VA contents, is studied by permeation measurements. A low density polyethylene LDPE, used as reference, is also studied. The diffusion of water is determined from transient permeation. For a better understanding of the role played by the structure and the surface of these copolymers whose crystallinity varies with the presence of VA groups, Differential Scanning Calorimetry and contact angle (surface free energy) measurements are performed. It is found for LDPE and 4.5% w/w VA membranes that the water diffusion coefficient decreases with increasing water concentration, while for 19% VA a constant diffusion coefficient is obtained. For membranes with 33, 50 and 70% w/w VA a diffusion coefficient which increases exponentially with the local water concentration is obtained. These results are explained by the formation at low VA content of small water clusters, clusters evidenced by means of IR spectrometry. On the other hand, the plasticization effect (concentration-dependent diffusion coefficient) is observed for VA content greater than 19% wt. VA is explained by the increase of the amorphous phase ratio, which allows an increase of the number of interactions between polar groups (carboxyl units in the statistical copolymer) and water molecules

Diffusion and permeation of water through unsaturated polyester resins—influence of resin curing

Abstract The diffusion and permeation properties of liquid water through an isophthalic-maleic acid-propanediol-based copolyester resin were studied with a highly sensitive permeameter. The value of the parameters of the exponential dependence of the diffusion coefficient on the water concentration decreases with the curing extent, except that of the plasticization coefficient, which decreases after a post-curing at 120°C. Infrared-spectrophotometric and calorimetric data show that the curing involves mainly a polymerization of styrene during the curing at 25°C, and a crosslinking by the opening of the double bonds on the polyester chains in the subsequent curing step at 80°C. The water sorption by the resin results in a 20°C-decrease in the glass transition temperature of the water saturated resin, leading to the diffusivity enhancement by the plasticization effect.

Surface modification by low-pressure glow discharge plasma of an unsaturated polyester resin: effect on water diffusivity and permeability

Abstract Unsaturated polyester resin (UPR) films have been modified by a tetrafluoromethane microwave plasma. The treated surface morphologies investigated by contact angle, atomic force microscopy and permeation measurements show that the CF 4 plasma treatment decreases drastically the surface energy by increasing the hydrophobic character. The surface modification due to plasma fluorination decreases the water content diffusing through the UPR film and the time lag diffusion coefficient and thus, the sorption kinetic. From these results, it is clearly shown that the CF 4 plasma treated layer improves drastically the barrier effects.

Water diffusion and permeability in unsaturated polyester resin films characterized by measurements performed with a water-specific permeameter: Analysis of the transient permeation

A water-specific permeameter was developed to study water diffusion in an unsaturated polyester; these polyesters are often used as high-barrier materials. Low water enrichment of a dry sweeping gas is measured via the dew point temperature, with two hygrometers, one of which is used because of its fast response and the other because of its accuracy. This high-performance device is just as suited to pervaporation as to permeation tests and allows the transient and stationary fluxes to be characterized. At first sight, the experimental data seem in good agreement with D = D0eγC. However, a more thorough study has shown a time-dependence of D.

Permeametric and microgravimetric studies of sorption and diffusion of water vapor in an unsaturated polyester

Abstract A detailed analysis of the sorption equilibrium and the diffusion of water vapor under different activities through an unsaturated polyester resin (UPR) has been undertaken by differential permeation and microgravimetry techniques. The BET-type III sorption isotherm obtained by microgravimetry was analyzed with the Zimm–Lundberg approach to determine the mean cluster size in the UPR film: the latter increases drastically with the water content in the film. The transient permeation flux can be well fitted when a concentration-dependent diffusivity of exponential type is used. From the water content at sorption equilibrium and the steady-state permeability, a mean diffusion coefficient for the steady state can be determined; its decrease with increasing water activity is consistent with the increase in the mean cluster size.

Sorption of glucose by an anion-exchange membrane in the borate form. Stability of the complexes and the facilitated transport of glucose

Abstract The reaction of glucose with the borate ion has been studied in an anion exchange membrane. Two complexes, BL− and BL2−, form in the membrane, and their corresponding stability coefficients β 1 ∗ and β 2 ∗ have been determined. The results have revealed that the BL− complex is much more stable in the membrane than BL2−, and the stability coefficient β 1 ∗ varies as a function of the relative proportions of the borate ion and the BL− complex. The facilitated transport of glucose was performed through an anion exchange membrane by using the borate ion as carrier; the content of the latter was fixed by the concentration of boric acid in solution. The permeance of the membrane was measured in two cases. In the first case, the boric acid concentration was fixed and the concentration of glucose varied. In the second case, the glucose concentration was fixed and the influence of boric acid concentration was examined.

Water and toluene barrier properties of a polyamide 12 modified by a surface treatment using cold plasma

Abstract. CF4 and CO2 plasma treatments have been used to modify the barrier properties of a polyamide 12 (PA12) towards permeant molecules, which present opposing characteristics: water and toluene. The surface modifications were observed by atomic force microscopy, X-ray photoelectron spectroscopy and surface Gibbs function measurements. Both treatments lead to different surfaces; one is rather hydrophobic (with CF4) whereas the other is more hydrophilic (with CO2. The effect of this modification on permeametric properties has been investigated by liquid water and liquid toluene permeation measurements. Our results show opposite effects of the two treatments. CF4 plasma treatment leads to a reduction of water and toluene permeability. With CO2 plasma treatment, in terms of permeation, two different behaviours were observed, an increase and a decrease of permeancy for water and toluene respectively. These results are in full agreement with those obtained for the surface characterization, and confirms change in the polymeric surface affinity for the permeant leading to a variation of the materials permeancy.

Carrier Facilitated Transport and Extraction Through Ion-exchange Membranes: Illustrated with Ammonia, Acetic and Boric Acids

Extraction and transport of a non-ionic substrate S can be facilitated through a charged membrane when a counter-ion Tz is a moving carrier for S. Coupling of transport and fast reaction is considered, with various values of stability constant. Consecutive reactions are investigated. Illustration, with S=NH3(in solution) + TZ=H+ or Ag+ and S=Acetic or Boric acid + TZ=OH−, is given. When polarization phenomena controls the transport, a critical flux Jcri is reached. Jcri is 80 to 200 times higher than passive flux.