An electrochemical Nafion® matrix oxygen sensor and the evaluation of oxygen permeation in coated films

A Nafion® matrix was used to prepare a small and simple oxygen sensor whose sensing electrode and counter electrode were made by r.f. sputtering of platinum deposits on both sides of the Nafion® membrane. The sensing current varied linearly with oxygen partial pressure. This sensor enabled an estimation of oxygen permeation in coated films at working conditions. The present method clarifies the correspondence between the permeation rate through the clear layer and the degree of deterioration of underlayered paint film.[/p]     

Spectrophotometric determination of water vapor permeation through polymer films

A novel method for measuring the permeation of water vapor through polymer films is described. A cellulose detector film incorporating cobalt chloride in a blue anhydrous from is sealed between two pieces of test film in a specially designed cell. The cell is placed in a controlled temperature and humidity cabinet, and the disappearance of the blue color of the cobalt chloride is recorded spectrophotometrically as water vapor diffuses through the test film into the detector film. This simple method of determining water-vapor-transmission rates is more rapid than standard gravimetric procedures because of the highly sensitive detection technique.     

Mathematical analysis of transport properties of polymer films for food packaging. VI. Coupling of moisture and oxygen transport using langmuir sorption isotherms

Deterioration of food products stored in flexible packaging materials can be attributed to the presence of both water and oxygen in the environment surrounding the food. Mathematical models for the simultaneous permeation of moisture and oxygen through the packaging polymeric film and subsequent adsorption on the food surface are presented for the case of competitive adsorption of the two diffusing species. These models are then used to predict internal packaging conditions over time for selected food products. Oxygen and moisture permeation are treated as independent phenomena, and the competition is regarded as occuring on a surface described by the Langmuir adsorption isotherm. It is found that for certain polymer physical properties and relative surface coverages, water and oxygen molecules can dislodge each other from the food surface and, even for situations where the initial partial pressure of oxygen is less than the external partial pressure, can cause an outward flow of the more weakly adsorbed material. This theory is then extended to incorporate varying external conditions of storage.     

Permeability of oxygen through polymers. I. A novel spectrophotochemical method

A novel method for the measurement of oxygen permeability through polymer membranes is described. It is based on monitoring the sensitized photo-oxygenation of a singlet oxygen acceptor in a detector layer sandwiched between a support and the polymer layer under test. The detector layer contains a sensitizer which on irradiation produces singlet excited oxygen from the ground-state oxygen available. The singlet oxygen reacts with an oxygen acceptor, the disappearance of which can be followed by spectrophotometry. In the photostationary state, changes in the acceptor absorbance are directly related to the overall flux of oxygen through the polymer membrane. It can be shown that the permeation coefficient P of oxygen is proportional to the rate of change in acceptor absorbance and to the inverse of the oxygen concentration in the surrounding atmosphere. It is given by the expression where ? is the molar extinction coefficient, ΔC is the difference in the oxygen concentration on the two sides of the polymer membrane, ΔD is the change in optical density during the time interval Δt, and l is the thickness of the polymer membrane. The method is comparatively simple and rapid and provides data for polymers that are difficult to study by more conventional methods. Oxygen permeabilities were measured for a group of water-soluble polymers.     

Analysis of oxygen permeation through dense ceramic membranes with chemical reactions of finite rate

The oxygen permeation through oxygen ionic or mixed-conducting ceramic membranes under reaction conditions was examined with a model taking into account of different electrical transport mechanisms (p-type and n-type transports) and finite reaction rate. It was demonstrated that with a reaction consuming oxygen in one side of the membrane, the oxygen partial pressure in the reaction side decreases and the oxygen permeation flux increases with the increase in the reaction rate for both the p-type and the n-type transport dominated mechanism. The increase in reaction rate causes a transition of the transport mechanism from p-type to n-type. This transition leads to an increase in the permeation flux by up to 30 times. This effect offers one explanation for the large discrepancies in published permeation data for membrane reactors of partial oxidation reaction employing an oxygen permeable dense ceramic membrane. For a membrane with a specific transport mechanism, the increase in the reactant partial pressure causes an increase in the reaction rate and oxygen permeation flux. However, the increase in the inlet inert gas amount has a complicated effect on the oxygen permeation flux because it lowers both oxygen partial pressure and the reaction rate at the same time.     

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.     

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma‐polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O₂ mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx‐deposited OPP film was decreased from 2230 to 37–52 cm³/m²/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm³/m²/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000     

An automated oxygen absorption instrument

Oxygen absorption is a widely used test for measuring polymer stability and antioxidant effectiveness. Commonly, periodic measurements are made using a mercury buret to measure the rate at which oxygen is taken up by the polymer. We designed and built a safe, dependable apparatus that continuously monitors the reaction of a hydrocarbon polymer with oxygen. The instrument operates by recording the frequency with which small, known volumes of oxygen are introduced into the sample tube to maintain a preestablished pressure in the tube. No operator time is required during the test. The instrument readings are readily converted to standard oxygen absorption curves.     

Plasma polymerized membranes and gas permeability. I

Gas permeability of composite membrane prepared by plasma polymerization of various organic compounds was studied. In the membrane, a pinhole-free polymeric thin film was formed on a porous substrate. This film below 0.2 μm in thickness had sufficient mechanical strength for gas separation. The composite membranes were recognized to have high permeability and high permselectivity. Especially, the membranes prepared from hexamethyldisiloxane showed high permeation rate for oxygen, and those prepared from 1-hexene or cyclohexane showed high permselectivity between oxygen and nitrogen. chemical structure of plasma-polymerized film prepared from hexamethyldisiloxane was similar to that of dimethylpolysiloxane with a crosslinking of the polymer. The high permeability and high permselectivity of this film is considered to be due to its structure as mentioned above.     

Mobility and solubility of antioxidants and oxygen in glassy polymers. III. Influence of deformation and orientation on oxygen permeability

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Plastic deformation under compression reduces this amount, whereas the application of a tensile stress increases it. Furthermore, orientation of a polymer introduces an anisotropy in the free volume. The change in free volume was monitored by oxygen permeation experiments. A clear correlation was found between the draw ratio, plastic deformation and stress on the one hand and oxygen permeability on the other. Since the mobility of oxygen is an important parameter for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.     

Permeation of oxygen through polyurethane–polyepoxide interpenetrating polymer networks

Oxygen permeation studies on polyurethane (PU)/polyepoxide (EP) interpenetrating polymer networks show that the increased crosslinking density owing to additional permanent chain entanglement (resulting from interpenetration) can decrease the coefficients of permeation, diffusion, and oxygen solubility. At 20% PU, at which the crosslinking density is maximum, these coefficients retain minimum values, while the tensile strength retains a maximum value.     

Effect of polymeric structure on the permeation rate in standard reference material sulfur dioxide permeation tubes

Liquid SO₂ sealed into tubes made of a fluorocarbon copolymer permeates the walls of the tube at a temperature-dependent but accurately reproducible rate. Sulfur dioxide dispensers made in this way are called permeation tubes and are useful for calibrating instruments that measure SO₂ concentrations in air. The National Bureau of Standards calibrates SO₂ permeation tubes and makes them available as Standard Reference Materials. The permeation rate in a batch of nominally identical tubes varies enough that each Standard Reference Material tube must be individually calibrated. Changes in the length or radial dimensions of the tubes are much too small to explain most of this variation. An excellent (negative) correlation is found between the measured permeation rate and the density of the polymer (or weight per unit length). Since both the measured density and the permeation rate for this semi-crystalline polymer depend upon morphological factors, but in different ways, x-ray diffraction measurements of the thickness and orientation of the lamellar crystals were made and a mathematical model was set up to identify the morphological factors which can cause variations in the permeation rate.     

Characterization of gas permeation in the pores of Zn(II)-based metal organic framework (MOF)/polymer composite membranes

ABSTRACT

The separation of greenhouse gases from industrial processes is an ongoing focus for research aimed at mitigating environmental impacts. As a result, it is important to develop experimental techniques for the characterization of the transport of gases through porous crystalline materials with potential applications in gas separations. We report on the fabrication and characterization of gas transport in supported Zn(II)-based MOF membranes. The MOF membranes were used to develop an approach to study membrane quality and determine the transport mechanism through the pores of the crystalline membrane. Membranes were synthesized via a solvothermal method with structural defects sealed by a low-permeability polymer coating, allowing for the measurement of permeation in materials that do not form uniform, defect-free films. Membrane permeation was proportional to the inverse square root of the molecular weight of the permeant gases, indicating that diffusion occurs via Knudsen diffusion. Membrane quality was studied via selectivity measurements as a function of temperature. A study of the gas permeation through a polymer coated sparse MOF membrane, was used to confirm that gas transport occurs through the pores of the MOF, rather than through pinholes or defects in the structure.     

Influence of microstructure on oxygen transport in perovskite type membranes

Abstract

The influence of bulk microstructure (grain size distribution, grain boundary length) on the oxygen transport properties of permeation membranes has been investigated. For this purpose, La_0.5Sr_0.5FeO_3-δ samples with different microstructures were prepared by varying sintering time and temperature. Average grain sizes, which ranged from 0.20 to 1.43 μm, were determined by SEM analysis. The oxygen transport properties of the samples were characterised by permeation measurements as a function of temperature in an air/argon oxygen partial pressure gradient. The fluxes presented a change in activation energy, which was attributed to a change in the rate limiting step, from bulk diffusion at lower temperature (< 850°C) to surface limitation at higher temperature (> 900°C). Only transport through the bulk was influenced by the microstructure, with the highest flux for the smallest grains. At 800°C, the fluxes were respectively 0.06, 0.03 and 0.01 μmol cm^-2 s^-1 through ≈ 1 mm thick samples with average grain sizes of 0.20, 0.63 and 1.43 μm respectively. This would imply that oxygen transport occurs more rapidly along grain boundaries than through the bulk. Grain boundary structure and composition were analysed by TEM.     

Permeation von flüssigem wasser bei eingetauchten,gefüllten polymerfilmen

The permeation rate of water in fully immersed, filled polymer films considerably exceeded that in films, of which one side adjoined water-saturated air or liquid water and the other dry air. This result may be explained by a preferential permeation in water-filled interspaces between the filler and the polymer matrix. In case of immersed alkyd resin films the permeation rate at first increased with rising pigment concentration and then tended to decrease at higher concentrations. On the other hand with different water concentration adjoining both sides of the film, the permeation rate steadily decreased with rising pigment concentration. There is some evidence that under these conditions a dry boundary layer exists at the downstream side in which no interspaces may be formed at the inner phase boundaries. This layer therefore acts as the main barrier against water permeation.     

Analysis of corrosion products beneath an epoxy-amine varnish film

In situ Raman analysis was applied to identify the corrosion products formed on iron coated with epoxy-amine varnish and exposed to sodium chloride solution saturated by hydrogen sulfide or carbon dioxide. The results showed the formation of iron sulfide or iron carbonate layer while electrochemical impedance spectrum predicted the polymer coating exhibiting an almost perfect protecting barrier property. It is concluded therefore, that the corrosion process involves the permeation of water and hydrogen sulfide at molecular state through polymer interstices whereas no ionic conduction is allowed to take place in the coating film. The corrosion process induces the complete delamination of the exposed coating area but as far as its integrity is respected (no macroscopic pores or crevices) the corrosion rate is very low, far from that expected from permeation measurements of H₂S.     

Scratch resistance and oxygen barrier properties of acrylate-based hybrid coatings on polycarbonate substrate

Organic/inorganic hybrid coating materials were synthesized using acrylate end-capped polyester, 1,6-hexanediolacrylate, tetraethoxysilane (TEOS), and 3-trimethoxysilylpropylmethacrylate (TMSPM). The hybrid materials were cast onto a polycarbonate (PC) substrate and cured by UV irradiation to give a hybrid film with covalent linkage between the inorganic and the organic networks. The coating layer was characterized by FT-IR and ²⁹Si-NMR, and pencil hardness and oxygen permeation rate of coated films were investigated. The pencil hardness of all samples examined in this study was higher than 1H, whereas that of uncoated PC substrate was 6B. The hardness enhancement after coating may due to incorporation of organic acrylate resin. The oxygen permeability coefficient of the film coated with hybrid material on 3-aminopropyltriethoxysilane (APTEOS) pretreated polycarbonate substrate was 1.67×10⁻³ GPU, the lowest value in this work, whereas that of uncoated PC substrate was 8.07×10⁻³ GPU. The lower oxygen permeation rates of these films are attributed to the good adhesion between organic/inorganic hybrid coating layer and PC substrate and a dense structure induced by an increase of network density.     

Optimized design of multilayer barrier films incorporating a reactive layer. III. Case analysis and generalized multilayer solutions

In part III of this series of articles, we present the analysis of transient permeation through two‐layer reactive–passive (RP) film designs, the analysis extension to multilayer structures, and optimized design solutions for multilayer barriers incorporating immobile noncatalytic oxygen scavenger within one of the layers. The reduction of oxygen ingress into a package within a certain timeframe depends on two factors: extension of the scavenger exhaustion time and reduction of the transient transmission rate through the film during that time. The optimal design for the scavenger exhaustion time involves exposure of the reactive layer to the package contents and its protection from high levels of environmental oxygen by the best possible passive barrier layer. The film barrier properties can be further optimized by the selection of the matrix material to place the scavenger in. Reducing the initial transmission rate requires the placement of the scavenger within a layer with the lowest diffusivity of the matrix polymer. When one chooses between two layers with different material transport properties in which to put the scavenger, the optimal solution for the ingress depends on the desired time to provide an improved barrier. The lifetime of the scavenger in the RP film is shortened for design 1, when the diffusivity of the reactive layer is smaller than that of the passive layer, compared to RP design 2, with the layer matrix sequence reversed, but the transient transmission rate is greatly reduced on average for the former. If the desired time to provide a barrier does not exceed the scavenger exhaustion time for RP design 1, the lowest diffusivity material should be used as a matrix for the innermost layer loaded with the scavenger. Otherwise, the highest possible passive barrier should be placed into the film external layer to minimize the total ingress during longer times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1966–1977, 2006     

Study on the inhibitory effect of DL-malic acid on the phase structure and combustion characteristics of coal

DL-malic acid (DMA), as a recognized antioxidant inhibitor and chelating agent in the food and chemical industries, has good application prospects in coal fire prevention and control. This paper investigates the impact of a DMA solution on the surface properties and phase structure of coal through a range of analytical techniques, including electron microscope scanning, particle size analysis, and x-ray diffraction. The thermal behavior characteristics of DMA-treated coal were analyzed using thermogravimetric experiments. The results show that after adding malic acid, the particle size of coal sample is reduced, the sphericity and roundness are reduced, and the pore size is increased. The hydroxyapatite and calcite components in coal were dissolved and consumed, and the calcite components were gradually depleted with the increase of DMA concentration. The flocculent structure produced by the condensation of the crushing residue and broken small particles are attached to the internal pores of coal, which reduced the coal oxygen contact sites and increases the content of the sealed solution, resulting in the increase of the thermal characteristic temperature of the coal and the inhibition of the oxidation heat generation process. DMA has obvious inhibitory effect on fresh coal and oxidized coal, and the inhibitory effect is stronger on high-temperature oxidized coal. Therefore, DMA can be effectively applied to the prevention and control of spontaneous combustion of residual coal in goaf. The research results provide a reference for the research of coal fire prevention technology and the preparation of environmentally friendly flame retardant materials.