Gas transport in polymer membrane at temperatures above and below glass transition point

The processes of gas sorption and permeation in a polymer membrane at temperatures above and below the glass-transition point were examined using poly-4-methylpentene-1 (glass-transition temperature reported to be 40°C) as a membrane material. The permeabilities to O₂ and N₂ were independent of applied gas pressure at every temperature; the mean permeability coefficient to CO₂ increased with increasing gas pressure. The logarithm of the mean permeability coefficient to CO₂ increased linearly with gas pressure due to the plasticization effect induced by sorbed CO₂. From the sorption isotherms for CO₂ at 20 and 30°C it was judged that the glass transition was brought about by sorbed CO₂ at temperatures below the glass-transition point of the pure polymer. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of novel X-type polyurethane containing dicyanovinylnitrocatechol of enhanced SHG thermal stability for electro-optic applications

Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass-transition temperature obtained from differential scanning calorimetry thermogram of around 113 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer film at 1,064 nm fundamental wavelength is around 5.72 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 7 °C higher than glass-transition temperature, and there was no SHG decay below 120 °C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.     

Sorption and permeation behavior for a gas in glassy polymer membrane near the glass transition temperature

The deviation from the conventional dual-mode sorption and mobility model for a gas in glassy polymer membranes has separately been studied thus far, and to simulate sorption and diffusion behavior, an extended dual-mode sorption model and a modified dual-mode mobility model, respectively, have been proposed independently. However, simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in cases of CO₂in poly-4-methyl-1-pentene membrane at 20°C and in polystyrene membrane at 60 and 70°C. The plasticization effect of sorbed CO₂ on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules exists. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of polythioetheramide from allylamine

Summary A novel polythioetheramide was synthesized from allylamine and 3-mercaptopropionic acid with a free-radical initiator. The thioether and amide linkages are formed from the free-radical addition of -SH group to double bond and the condensation between -NH₂ and -COOH, respectively. The free-radical addition gives almost exclusively anti-Markovnikov product. The resulting polymer has a glass-transition temperature of 8.5 °C and a melting point of 145 °C. Though the introduction of the thioether linkages increases flexibility, the polymer retains good solvent resistance. Received: 1 June 1998/Revised version: 24 August 1998/Accepted: 27 August 1998     

Preparation of zeolite filled glassy polymer membranes

The incorporation of zeolite particles in the micrometer range into polymeric matrices was investigated as a way to improve the gas separation properties of the polymer materials used in the form of membranes. The adhesion between the polymer phase and the external surface of the particles appeared to be a major problem in the preparation of such membranes when the polymer is in the glassy state at room temperature. Various methods were investigated to improve the internal membrane structure, that is, surface modification of the zeolite external surface, preparation above the glass-transition temperature, and heat treatment. Improved structures were obtained as observed by scanning electron microscopy, but the influence on the gas separation properties was not in agreement with the observed structural improvements. © 1994 John Wiley & Sons, Inc.     

PBI‐Based Polymer Membranes for High Temperature Fuel Cells – Preparation,Characterization and Fuel Cell Demonstration

Proton exchange membrane fuel cell (PEMFC) technology based on perfluorosulfonic acid (PFSA) polymer membranes is briefly reviewed. The newest development in alternative polymer electrolytes for operation above 100 °C is summarized and discussed. As one of the successful approaches to high operational temperatures, the development and evaluation of acid doped polybenzimidazole (PBI) membranes are reviewed, covering polymer synthesis, membrane casting, acid doping, physicochemical characterization and fuel cell testing. A high temperature PEMFC system, operational at up to 200 °C based on phosphoric acid‐doped PBI membranes, is demonstrated. It requires little or no gas humidification and has a CO tolerance of up to several percent. The direct use of reformed hydrogen from a simple methanol reformer, without the need for any further CO removal, has been demonstrated. A lifetime of continuous operation, for over 5000 h at 150 °C, and shutdown‐restart thermal cycle testing for 47 cycles has been achieved. Other issues such as cooling, heat recovery, possible integration with fuel processing units, associated problems and further development are discussed.     

Synthesis and luminescence properties of long-chain (2,7-carbazolyl)-adamantane copolymers

Several long-chain (2,7-carbazolyl) adamantane copolymers, with molecular weight ranging from 4500 to 6000, were synthesized by palladium-catalyzed Suzuki reaction using 1,5-bis (4-bromophenyl) adamantane and N-(2-ethylhexyl)-2,7-carbazole as building molecules. The copolymers were characterized by infrared, ultraviolet, nuclear magnetic resonance (NMR), fluorescence spectroscopies, and thermal analysis. It was found that the introduction of adamantyl group into the backbone of conjugated carbazole polymer significantly improves the thermal stability and spectral stability of the copolymer. These copolymers giving high color purity showed excellent comprehensive performance: the thermal decomposition temperature is up to 409 ~ 432 °C, glass-transition temperature is about 83 ~ 162 °C, fluorescence quantum efficiency is as high as 0.76 ~ 0.85. Hence, the synthesized copolymers have great potential for being used as new blue-light-emitting materials.     

Effect of liquid media on the ultimate strength characteristics of viscofluid polymers in uniaxial extension

The fracture properties and deformation behaviour of a linear amorphous polymer (1,2-polybutadiene) above the glass-transition temperature (?18°C) in liquid media have been studied. In accordance with data published earlier it is found that when fractured above T_g polymers behave like cured elastomers. Experiments conducted in low-molecular alcohols at 10°C show that the ultimate strength, durability (time-to-fracture) and development of irrecoverable deformation of viscous flow depend very strongly on the nature of the liquid medium, whereas the development of the elastic component of deformation is independent of the nature of the alcohols. It has been established that the dependence of durability on true fracture stress for the polymer studied is described by a power function. A simple correlation has been found between the surface tension at the polymer-liquid interface and the durability and ultimate strength of the polymers.     

Bioethanol as a promising fuel for fuel cell power plants

The catalytic reaction of steam reforming of bioethanol for the production of a hydrogen-containing gas in a temperature range from 300 to 700°C is studied. Copper-, nickel-, cobalt-, platinum-, and rhodium-containing catalysts supported on different substrates, including metal grids, are tested. Comparative analysis of the methods of bioethanol processing to a hydrogen-enriched gas for feeding high-temperature proton-exchange polymer electrolyte membrane fuel cells is performed.     

Matrimid‐based carbon tubular membranes: The effect of the polymer composition

In this article, we present a development study of new membrane materials and enhancements of productive membranes to improve the current performance of polymeric membranes. Carbon membranes are a promising material for this matter as they offer an improvement in the gas‐separation performance and exhibit a good combination of permeability and selectivity. Carbon membranes produced from the carbonization of polymeric materials have been reported to be effective for gas separation because of their ability to separate gases with almost similar molecular sizes. In this study, a carbon support membrane was prepared with Matrimid 5218 as a polymeric precursor. The polymer solution was coated on the surface of a tubular support with the dip‐coating method. The polymer tubular membrane was then carbonized under a nitrogen atmosphere with different polymer compositions of 5–18 wt %. The carbonization process was performed at 850°C at a heating rate of 2°C/min. Matrimid‐based carbon tubular membranes were fabricated and characterized in terms of their structural morphology, thermal stability, and gas‐permeation properties with scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and a pure‐gas‐permeation system, respectively. Pure‐gas‐permeation tests were performed with the pure gases carbon dioxide (CO₂) and N₂ at room temperature at a pressure of 8 bar. On the basis of the results, the highest CO₂/N₂ selectivity of 75.73 was obtained for the carbon membrane prepared with a 15 wt % polymer composition. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42394.     

Evidence of dual mobility in sulfur dioxide-polyarylate system: An integral sorption analysis

Integral sorption/desorption measurements were carried out for the sulfur dioxide-glassy polyarylate polymer system at 25°C, 40°C, 55°C, and 63°C. The transport of sulfur dioxide in the glassy polyarylate polymer was governed by Fickian diffusion. The effective diffusion coefficient of sulfur dioxide increased with increasing penetrant concentration. The concentration dependence of the effective diffusion coefficient is explained on the basis of the partial-immobilization model developed by Paul and Koros. The mobility of the molecules sorbed in the Langmuir mode is shown to be significantly lower than the mobility of the molecules in Henry's law dissolution mode. The predictions of permeability values as a function of upstream gas pressure are presented. The equilibrium sorption isotherms for this system are well represented by the dualmode sorption model. The eltergetics and the temperature dependence of the dual-mode parameters are also discussed.     

Effects of Thermal Treatment on Gas Transport Through Porous Silica Membranes

Abstract

The effects of thermal treatment from 180°C to 1150°C on the gas transport properties of porous silica membranes were systematically studied for various gases. The permeance of all gases, except for CO₂, has a maximum at 800°C. The CO₂ permeance was constant from 180°C to 600°C and then decreased monotonically. Membranes thermally treated at 1150°C did not exhibit any gas permeation because of pore collapse. The gas transport behavior follows a combination of Knudsen diffusion and surface diffusion for all gases tested except for carbon dioxide. The permeation of carbon dioxide is strongly affected by capillary condensation. We propose a new transport model composed of two components; that is, the Knudsen diffusion factor, α, and the surface diffusion factor, β. A transition was observed for α and β at around 800–900°C, which is close to the strain point of the membrane. This transition treatment temperature can be correlated with the changes in gas permeance. The model allows qualitative evaluation of gas transport through porous membranes regardless of their actual microporous structures.     

Thermal,stability, morphological,and conductivity characteristics of polypyrrole prepared in aqueous medium

The aqueous polymerization of pyrrole with varying FeCl₃/Py mol ratio produces black insoluble powders. IR characterization reveals the shifting of the N? H stretching band to higher frequency with increasing FeCl₃ amount in the feed composition due to lowering of intermolecular H-bonding. SEM shows a spongy texture of the polymer. TGA indicates the initial decomposition temperatures (180°–237°C) to be somewhat dependent on the FeCl₃/Py feed ratio. DSC suggests the glass-transition temperature to be in the range 160–170°C for the polymers prepared with various feed compositions. The conductivity is also dependent on the FeCl₃/Py feed composition and levels off at a value of ～3 ohm^?1cm^?1. © 1994 John Wiley & Sons, Inc.     

Inorganic Membrane Technology

Abstract

The objective of this program is to develop a variety of inorganic based high temperature separation membranes. Organic membranes are limited by temperature (<100°C) and chemical environments, and are unsuitable for high temperature applications. The higher temperature stabilities of inorganic materials make them ideal candidates for high temperature membrane applications. Polymers with inorganic backbone structures, such as the polyphosphazenes, are being examined for mid-temperature membrane separation applications (100°C–350°C). Metallic and ceramic membrane materials are being examined for high temperature separation applications (350°C–1000°C). The liquid and gas membrane test systems developed for this program are described. Preliminary results on the separation properties of poly[bis(2,2,2 trifluoroethoxy)phosphazene± membranes are reported for dilute aqueous methanol, ethanol, isopropanol, and phenol feedstreams.     

Synthesis of novel polyimide with highly enhanced thermal stability of second harmonic generation for electro-optic applications

2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine to yield novel Y-type polyimide 5 containing 2,3-dioxybenzylidenemalononitrile group as NLO-chromophores, which constitute parts of the polymer backbones. The resulting polyimide 5 was soluble in polar solvents such as acetone and N,N-dimethylformamide. Polymer 5 showed a thermal stability up to 330 °C in thermogravimetric analysis thermogram with T _g value obtained from differential scanning calorimetry thermogram near 190 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer films at the 1064 nm fundamental wavelength was around 3.15×10^-9 esu. The dipole alignment exhibited a thermal stability even at 20 °C higher than the glass-transition temperature, and there was no SHG decay below 210 °C because of the partial main chain character of polymer structure, which was acceptable for nonlinear optical device applications.     

Preparation and characterization of electropolymerized poly(N-substituted methacrylamide) matrices on graphite fibers

2- or 4-carboxyphenyl methacrylamide (2- or 4-CPM) was successfully electrocopolymerized with either methylmethacrylate (MMA) or N-phenylmaleimide (NPMI) to form a thick thermoplastic matrix with high glass-transition temperature (200–300°C), on Hercules AS-4 graphite fibers. The dependence of the diffusion of active species through the coating upon the solvent/water ratio in the cell was estimated from the electrochemical diffusion behavior of hexacyanoferrate (III) ions. A higher solvent/water ratio helped to increase polymer weight gain by increasing the solvent swelling and increasing the diffusion coefficient of active species. A highly solvent-swollen polymer layer promoted the rate of polymer weight gain. The copolymer composition of 4-CPM/MMA and 4-CPM/NPMI polymers was random, and the effects of variables were consistent with free-radical polymerization kinetics. The electropolymerization rates of 4-CPM/MMA and 4-CPM/NPMI were increased by increasing current density and monomer concentration. For a slight temperature increase (from 28–45°), electropolymerization rate and polymer weight gain increased dramatically for the 4-CPM/NPMI system. © 1993 John Wiley & Sons, Inc.     

A compatible and crosslinked poly(2-allyl-6-methylphenol-co-2,6-dimethylphenol)/polystyrene blend for insulating adhesive film at high frequency

A polymer blend consisting of poly(2-allyl-6-methylphenol-co-2,6-dimethylphenol) (APPE) and polystyrene (PS) with additives such as 1,2-bis(4-vinylphenyl)ethane, cyanate ester, and nitrile butadiene rubber was formulated as an insulating high-frequency adhesive film. The polymer blend of APPE and PS showed very high compatibility to these additives, and the resulting thermally cured polymer blend exhibited an excellent mechanical strength, as shown by an ultimate tensile strength of 51 MPa and Young's modulus of 1.4 GPa. Moreover, the blend exhibited very good dielectric properties, with a dielectric constant of 2.3 and a dissipation factor of 0.0030 at 10 GHz. The glass-transition temperature of the cured polymer blend was 141 °C, as determined by differential scanning calorimetry, and the 5% weight loss temperature was 372 °C, indicating relatively high thermal resistance characteristics. Furthermore, its peel strength to a copper foil reached 0.80 N/mm. The present study suggested that the thermally cured APPE/PS polymer blend with additives will have potential applications for the next-generation high-frequency adhesives in microelectronic circuits. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47828.     

A macrokinetic approach to crystallization applied to a new thermoplastic polyimide (New TPI) as a model polymer

The application of a new macrokinetic approach to polymer crystallization is applied in this work to a new thermoplastic polyimide (New TPI) recently developed as a matrix of advanced polymer matrix composites. The slow crystallization kinetics presented by New TPI in the entire range between the glass-transition temperature and the melting point makes TPI an excellent model polymer for testing crystallization models. In the approach presented here the variation of the induction time with the temperature is included in the Nakamura model for nonisothermal crystallization, and a simplified expression of the kinetic constant as a function of the temperature is adopted. The proposed model is verified through a comparison with a complete set of experimental data, ranging from the melting point to the glass-transition temperature of the polymer, obtained in isothermal and nonisothermal conditions. Moreover phase transformation diagrams (TTT and CCT plots) are presented, providing a fundamental tool for understanding the crystallization behavior of semicrystalline matrices and to determine the more appropriate processing conditions. © 1995 John Wiley & Sons, Inc.     

Metallic-lithium, LiFePO4-based polymer battery using PEO—ZrO2 nanocomposite polymer electrolyte

A study of the electrochemical properties of a PEO-based polymer electrolyte with nanometric ZrO₂ as ceramic filler has been carried out in order to confirm an earlier reported model dealing with the role of ceramic fillers within PEO-based polymer electrolytes as components that enhance such properties as conductivity, lithium transference number, compatibility with lithium metal electrodes and cyclability. A prototype of a lithium polymer battery, based on a membrane made from a nanocomposite polymer electrolyte doped with ZrO₂, utilizing LiFePO₄ + 1%Ag as cathode, has been assembled and galvanostatically cycled, resulting in excellent performance at temperatures ranging from 100 °C to 60 °C (close to the crystallization temperature of PEO).     

Torsional braid analysis of bitumen-liquid rubber mixtures

The performance of liquid rubbers as low-temperature plastcizers for bitumen was evaluated by the torsional braid technique developed by Gillham. The low-temperature dynamic mechanical properties of bitumen-liquid rubber mixtures were measured from ambient to ?100°C and compared with the corresponding fracture behavior using a modified Fraass test. Microscopic observation of the mixture revealed that the liquid rubber was partially soluble in the bitumen at 23°C and at concentrations greater than 10 percent tended to form colloidal dispersions of rubber particles having mean diameters of approximately 10 μm. The loss tangent maxima shifted to lower temperatures and became less pronounced as the concentration of liquid polybutadiene increased. The colloidal rubber dispersion further contributed to the ductility and reduced the brittle temperature of the bitumen at ?30°C at 20 percent liquid rubber concentration. The reduction in the brittle temperature of the bitumen is related to the glass-transition temperature of the added rubber, those rubbers having, the lowest glass-transition temperatures being most efficient. Such modifications are necessary to reduce the tendency of asphaltic paving materials to crack in cold climates.