Permeation of gases through modified polymer films. V. Permeation and diffusion of helium,nitrogen, methane,ethane, and propane through γ-ray crosslinked polyethylene

The permeation and diffusion of helium, nitrogen, methane, ethane, and propane through γ-irradiated polyethylene films were investigated. These studies were carried out with two objectives in mind: (1) to determine the effect of crosslinking by γ irradiation on permeability and diffusivity using the gas molecules as molecular probes; and (2) to study the plasticizing effects of the low hydrocarbons on the polyethylene film. The γ-ray-induced crosslinking efficiency of polyethylene was investigated in the following irradiation atmospheres: vacuum, acetylene, and nitrogen–acetylene mixtures. Results showed that irradiation in acetylene decreased the crosslinking efficiency while an acetylene–nitrogen atmosphere increased the efficiency compared to irradiation in vacuum. Both the permeation constants and the diffusion coefficients were found to decrease with increasing irradiation dose while the activation energies increased. The permeation constants of the organic gases through polyethylene increased with molecular diameter while the diffusion coefficients decreased. This increase in permeability was attributed to an increase in the solubility due to solubilization of the membrane by the penetrant. For example, the molecular diameter of propane is 4.397 Å compared with 2.807 Å for methane; however, propane permeated the polyethylene film at a rate twice that of methane. Nitrogen and methane have approximately the same molecular diameters—2.7085 and 2.807 Å, respectively—but owing to the plasticizing effect of methane, it permeated the film at a rate three times greater than that of nitrogen. It is interesting to note that the stronger the plasticizing ability of the penetrant, the greater the effect of the irradiation dose. The permeability of propane decreased by 40.7%, while the permeability of helium decreased by 6.4% after an irradiation dose of 50 Mrad.     

SORPTION,DIFFUSION, AND PERMEATION OF CHLORINATED HYDROCARBON VAPORS THROUGH NATURAL RUBBER,EPOXIDIZED NATURAL RUBBER,AND THEIR BLENDS

The study investigates the transport process of various chlorinated hydrocarbons through natural rubber (NR), epoxidized natural rubber (ENR), and their blends. The effect of structure and morphology of the membranes on the transport parameters has been investigated. Sorption coefficient is found to increase and the permeability coefficient shows the reverse trend with increasing epoxy content. As the mol% epoxidation increases, the polymeric network structure becomes more compact, which leads to a decrease in the diffusion coefficient, which ultimately results in a low permeation coefficient. The morphology of NR/ENR blends has been investigated by combining scanning electron microscopy with permeability measurements. The permeation coefficient is found to be minimum for the NR/ENR 70/30 composition; a 50/50 composition shows the maximum. The heterogeneous morphology of 70/30 NR/ENR blend results in the low permeability coefficient, whereas the co-continuous nature of the 50/50 composition accounts for the maximum permeability. Permeability measurements provide the most useful information about the way morphology is changing with composition of the blends and about the composition corresponding to the maximum level of co-continuity of the two phases.     

Preparation and properties of polyurethane nanocomposites of novel architecture as advanced barrier materials

The helium gas permeation through polyurethanes (PU) having novel microstructures derived from different polyols (varying from linear to hyperbranched) in the presence and absence of modified and unmodified nanoclays has been studied thoroughly in this paper. The permeation rate of helium gas decreases from linear to fourth generation polyols (PU₄₀) by about 80% due to increase in the crosslinking density. Similarly, the permeation rate of 8 wt% clay filled third generation hyperbranched PU dramatically decreases by about 76% in comparison to the unfilled PU. Gas-impermeable clay platelets in the PU matrix form tortuous pathways that further retard the progress of gas molecules. In addition, the well dispersed modified nanoclays contribute to improvement of the permeability properties to a great extent when compared with the aggregated unmodified ones. Further, interaction between the clays and the PU matrix plays a great role. Good correlation between dispersion of nanoclays in the PU matrix, as characterized by high resolution transmission electron microscopy and atomic force microscopy, and barrier resistance has been established. The permeation results have been compared with the different contemporary permeability models. The results are in line with the prediction by the Gusev-Lusti, the Nielsen and the Cussler (regular array) models at lower concentration of clay.     

Oxygen permeation through Teflon–PFA tubing into flowing helium

The permeability coefficient for oxygen diffusing through a sample of Teflon-PFA tubing has been determined experimentally. The source of the diffusing oxygen was ambient air surrounding a 1.835 m length of PFA tubing. Pressurized high purity helium was directed through the center of the PFA tubing. Oxygen permeating from the low pressure ambient air source, through the PFA tubing, and into the flowing pressurized helium was observed in the effluent gases as they passed through a trace oxygen analyzer. By this means, oxygen concentrations in the effluent helium were determined as a function of varying helium flow rates, at helium gas pressures of 1.92 and 4.40 atm (absolute), within the tubing bore. All measurements were carried out at ambient temperatures of 23.5 ± 1.3°C. In addition, a theoretically related graphical method of evaluating the experimental data was employed to actually determine the oxygen permeability coefficient for this system.     

Modification of poly(ethylene terephthalate) (PET) using linoleic acid for oxygen barrier improvement: Impact of processing methods

Poly(ethylene terephthalate) (PET) is commonly used in the packaging industry; however, there is considerable interest in reducing the rate of oxygen permeation through PET to extend product shelf life. One method being employed to improve oxygen barrier is the introduction of reactive compounds to bind the oxygen permeating through the polymer. This work investigates a naturally occurring oxygen scavenger, linoleic acid (LA), which was incorporated within blown PET bottles using two different processing schemes. The LA was incorporated within PET at 0.5% by weight using both by blending and reaction of carboxyl end of LA and hydroxyl end of PET. The effect of LA on the thermal, mechanical properties, and oxygen permeation were determined. There was a decrease in oxygen permeability for the PET/LA samples with little change in physical properties relative to base PET. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45023.     

Molecular dynamics simulation of gas permeation phenomena in a microporous silica membrane

In this study, the permeation phenomena of helium, nitrogen, and carbon dioxide gases are observed through dual control volume grand canonical molecular dynamics method, which is a combination of molecular dynamics simulation and grand canonical Monte Carlo method. Adsorption isotherm and angle distribution inside pores are analyzed to identify the permeation characteristics. Also, permeability and separation factor of pure gases and mixtures are investigated for the change of pressure, temperature, and composition. The predicted properties are compared with experimental data. The separation mechanisms of pure and mixture systems are identified through the analyses of simulation results.     

Amorphous hydrogenated carbon films as barrier for gas permeation through polymer films

The influence of amorphous hydrogenated carbon (a-C:H) coatings on the gas permeation through polymer films was investigated. a-C:H films were deposited from a 13.56-MHz RF glow discharge in methane or acetylene atmosphere. Thin poly(ethylene terephthalate) and polyimide foils were used as substrates. The permeation of the gases H₂, N₂, O₂ and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and density of the a-C:H films. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The a-C:H/PET surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Multilayer structures comprising different types of a-C:H films were also investigated. A reduction of the permeability coefficient by 80% for hard, dense and 94% for soft, polymer-like layers was found. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H film density. This unexpected result is attributed to the appearance of a network of deep cracks spread out over the whole coating.     

Crack propagation analysis of SiCf/SiC composites by gas permeability measurement

Permeability of helium gas through the NITE-SiC_f/SiC composites after applying tensile stress was measured experimentally in a vacuum apparatus. Tensile stress equal to 1.1-1.2 times the proportional limit stress (PLS) was applied parallel to the direction of the reinforced fiber. Results of the permeability experiments revealed that the permeability rapidly increased when threshold stress was applied on the specimens. The permeability of helium gas was governed by the narrowest diameter of the permeation pathway. In the case of NITE composites, the diameter of the pathway was calculated to be below 0.65 μm. The NITE composites exhibited superior performance even when the applied stress was greater than 1.2 times the PLS. Fiber bundles considerably magnified the permeability of helium gas because of the relatively large pore size of the intra-fiber bundles. Transverse cracks propagated with increasing stress and they connected fiber bundles when the applied stress was 1.10-1.15 times the PLS.     

ON THE PERMEATION OF SOME GASES THROUGH THE LAMELLAE OF STATIC FOAMS. A PRELIMINARY APPROACH

Basing on the capillary method for the determination of foam bubble size, a method was proposed for establishing values of permeability coefficients of several gases. The permeability coefficients of He, Ar, H₂, N₂, CH₄ through the lamellae of static foam bubbles were preliminarily determined using this method.

A rough dependence of the N₂ permeability coefficient through the lamellae of static foam bubbles on the foam wetness and surfactant concentration was also found.

The results obtained lead to the conclusion that the Princen-Mason diffusion model of gas permeation through an isolated soap film was inadequate in the case of permeation through lamellae of bubbles forming a static foam.

A hypothesis that the gas permeation through the lamellae of a static foam is primarily caused by liquid convection in the lamellae core was put forward.     

Permeability of water and water vapor through cellulosic membranes

To elucidate the water transport mechanism through homogeneous membranes, water and water vapor permeation through crosslinked cellulose membranes, cellulose diacetate, and cellulose triacetate membranes are studied. It is found that the water flux increases with the degree of hydration; and as for cellulose membranes, the degree of hydration is an increasing function of the degree of crosslinking. Activation energy of hydraulic permeability (K_w) is not equal to that of purely viscous flow, and is smaller than that of the water vapor diffusion coefficient (D?) for all membranes. The free-volume concept relating the molar frictional coefficient to temperature and to degree of hydration explains reasonably the temperature dependence of hydraulic permeability and of water vapor diffusion coefficient and gives adequate values for the fractional free volume of the system. The critical volume V^*, appearing in the Cohen-Turnbull expression between friction coefficient and free volume fraction, may be considered as the size of the cluster of water molecules. The value of V^* in the case of hydraulic permeability is larger than that for water vapor diffusion by several times. Furthermore, the value V^* increases with increase of degree of hydration for water permeation and water vapor diffusion.     

Sorption and permeation behavior of water vapor and carbon dioxide gas through ethylene ionomer membranes

Sorption and permeation of water vapor and carbon dioxide gas through ethylene ionomer membranes were studied as a function of pressure. Water sorption increased with an increase of the acid content and especially degree of neutralization of ethylene ionomers. The sodium salt ionomer enhanced water sorption compared to the zinc salt ionomer. However, there was no remarkable difference of permeability coefficient of water vapor through the sodium and zinc ionomer membranes. Diffusion coefficient of the sodium salt ionomer is one order smaller than that of zinc salt ionomer, corresponding to an immobilized water structure in the sodium salt ionomer. Differential scanning calorimetry studies on water sorbed to membrane manifested that water sorbed was almost nonfreezable. Sorption of carbon dioxide gas in ethylene ionomers was a dual-mode type. The pressure dependence of permeability coefficient of carbon dioxide gas was interpreted in terms of a partial immobilization model, independent of the kind of the metal salt in ethylene ionomer.     

Evaluation of transfer of wine aroma compounds through PET bottles

Aroma compound could be lost during food storage in polymer packaging by transfers through material. The aim of this study was to develop a method that allows evaluating wine aroma compounds permeation through active PET bottles. A semiquantitative method has been adapted to the system. Results showed a regular permeation of all studied aroma compounds but a high variation between replicates. In active PET bottle containing 1% of oxygen scavenger, amount lost by permeation after 12 months storage at 20°C was about 6.13 ± 0.37 µgbottle^?1. When 50% of recycled PET was added to active PET bottle, permeation rate was increased about 15%. The study of sorption of aroma compounds in both polymer matrices did not allow to explain this difference of permeation, but the structure of recycled PET seemed to induce modifications in aroma compound diffusion through active PET which could increase transfer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41784.     

Structural, optical, thermo-mechanical and transport properties of ion irradiated polymer membranes

Summary The modifications in PET induced by swift heavy ion irradiation are analyzed. PET membrane of 15 μm was irradiated by Cl⁹⁺ ions of 100 MeV at TIFR Mumbai. The changes due to exposure to high-energy ions were investigated by Fourier Transform Infrared (FTIR) and Ultraviolet/ Visible absorption (UV/VIS) spectroscopies, X-Ray diffraction technique, dynamic mechanical analysis and by the gas permeation. A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption and FTIR spectra. Gas permeation through these membranes before and after irradiation using hydrogen and carbon dioxide gases shows that permeability for both gases increased after irradiation but permeability for hydrogen is higher than carbon dioxide due to its small molecular size.     

Permeation of water vapor through cellulose triacetate membranes in hollow fiber form

A modification of the carrier gas method for measuring permeability of a hollow fiber to a vapor is described with particular application to water vapor permeation through asymmetric cellulose triacetate in hollow fiber from. Conventional methods are inadequate because the high flux of permeation vapor combined with its low pressure on the permeate side and the small diameter of the fiber lead to an excessive buildup of pressure in the permeate stream—in some cases so great as to render much of the fiber length ineffective. The method described in this paper involves the permeation from the outside to the inside of the fiber of a binary mixture consisting of the water vapor and a fairly highly permeable carrier (helium). There is a significant pressure drop along the fiber, but a theoretical treatment is presented to take this into account and to permit a determination of the vapor permeability. Experiments at 35°C over a range of water vapor pressures up to 1.7 cm Hg gave a water flux of 9 × 10^?3 cc(S.T.P.)/cm²-sec-cm Hg, with an apparent slight decrease with increasing pressure. Over the same range of water vapor pressure the helium flux decreased from 2.3 × 10^?4 to 1.85 × 10^?4 cc(S.T.P.)/cm²-sec-cm Hg.     

Water sorption and diffusion through saturated polyester and their nanocomposites synthesized from glycolyzed PET waste with varied composition

A new system of saturated polyester and their nanocomposites synthesized from glycolyzed PET with varied composition is investigated for the sorption and diffusion studies in water. The kinetics of sorption is studied by using the equation of transport phenomena. The values of ‘n’ from transport equation are found to be below ‘0.5’, showing the non-Fickian or pseudo-Fickian transport in the polymer. The dependence of diffusion coefficient on composition and temperature has been studied for all polymeric samples. The diffusion coefficient of saturated polyester samples decreases with an increase in glycolyzed PET contents. The nanocomposite samples show less diffusion coefficient than pristine polymer and it decreases with an increase in nano-filler up to 4 wt%. The diffusion coefficient increases with an increase in temperature for all the samples. The sorption coefficient shows a little change with variation in composition as well as temperature for all the samples and it is in a range of 1. The activation energy for diffusion and permeation is positive for all the samples. The heat of sorption is also positive for all the samples, indicating Henry type mode of sorption.     

Permeation of hydrocarbon gases through polymer membranes

Experimental results are presented for the permeation of propane and ethylene through polyethylene membranes and for the permeation of propane through “Saran” in the temperature range from —10 to 20°C and the pressure range from 20.0 to 50.0 psig. The flux of propane through polyethylene exhibits a minimum as the temperature approaches the condensation temperature. No such minimum was observed either for the flux of ethylene through polyethylene or for propane through “Saran”. The permeability coefficients for propane through polyethylene are compared with those predicted on the assumption of a diffusion coefficient exponentially dependent on the concentration of permeability.     

Helium permeability of polymer materials as liners for composite overwrapped pressure vessels

Polymers have been identified as replacement materials for metallic liners in composite overwrapped pressure vessels (COPVs) for future space launchers. PEEK, Nylon, and PVDF plastics formed from base powder grades have been permeability tested to determine their susceptibility to the diffusion of helium through flatwise panel cross sections. Permeability, diffusion, and solubility coefficients have been obtained for each material with PVDF and PA11 grades showing the lowest permeability coefficients and hence the best barrier properties to permeation. Crystallinity percentages and internal air void contents in the polymer samples have also been used to assess the differences in permeability between materials with an analysis of void dispersion effects given through X‐ray CT scanning techniques. The measured permeability coefficients have been used to assess the ability of all materials tested to act as a functional polymer liner in a standard COPV with final leak rates predicted based on liner thicknesses and weights. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43675.     

Organic vapor permeation through natural rubber/poly(ethylene‐co‐vinyl acetate) blend membranes

Natural rubber/poly(ethylene‐co‐vinyl acetate) (NR/EVA) blend membranes, crosslinked with dicumyl peroxide, have been prepared and tested for vapor permeation characteristics. The effects of structure and morphology of the blend membranes on the permeability were investigated. The permeability was found to decrease with increase in EVA content which has been attributed to the semicrystalline nature of EVA. The permeation process has been observed to be controlled mainly by the molecular mass of the penetrants. In the case of benzene/acetone mixtures, it has been found that when acetone concentration increases the vapor permeation rate decreases. This clearly indicates less interaction of acetone towards NR/EVA membranes. For supporting all the observations, the parameters such as swelling coefficient and permeability coefficient have been calculated. POLYM. ENG. SCI., 48:198–202, 2008.© 2007 Society of Plastics Engineers     

Experimental study of helium leakage parameters in flexible composite

The helium leakage characterizations of flexible composites are experimentally studied in this article. Three data processing techniques (Defining method, Fourier series method, and Fast series method) are used to evaluate the helium leakage parameters including the diffusion coefficient D, the solubility S, and the permeant rate k. The chamber pressure variation for helium permeation in flexible composite is measured by the differential pressure method. The results indicate that Fast series method is an effective technology in extracting the helium leakage parameters for flexible composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

三甲基硅基甲基纤维素的合成及膜的富氧性能

引言 在分离膜研究与发展的历史上,天然高分子是最早使用和进行改性的膜材料.纤维素及其衍生物具有原料丰富易得、成本低、无污染、成膜性好等优点,至今仍作为常用的膜分离材料[1].由于纤维素中存在大量的羟基和强的分子间氢键,氧透过性能并不理想,因此很少将纤维素直接用作气体分离尤其是氧氮分离的膜材料.近来,有专利报道对纤维素进行改性修饰,在羟基上连上含硅的基团如三甲基硅基,可以获得好的富氧性能[2].但由于该反应属于非均相反应,这一制备方法的实施和验证有困难.本文选用能够溶于有机溶剂的甲基纤维素(MC)为原料,以六甲基二硅胺烷(HMDS)作为三甲基硅基化试剂,通过均相反应很容易地制备了具有较高的取代度和良好的有机溶剂溶解性能的三甲基硅基甲基纤维素(TMS-MC).经溶液浇铸成膜,对其富氧性能研究后发现,与甲基纤维素膜相比,该膜的透氧系数和氧氮分离系数分别得到显著改善.