The morphology and gas‐separation performance of membranes comprising multiwalled carbon nanotubes/polysulfone–Kapton

The development of desirable chemical structures and properties in nanocomposite membranes involve steps that need to be carefully designed and controlled. This study investigates the effect of adding multiwalled nanotubes (MWNT) on a Kapton–polysulfone composite membrane on the separation of various gas pairs. Data from Fourier transform infrared spectroscopy and scanning electron microscopy confirm that some studies on the Kapton–polysulfone blends are miscible on the molecular level. In fact, the results indicate that the chemical structure of the blend components, the Kapton–polysulfone blend compositions, and the carbon nanotubes play important roles in the transport properties of the resulting membranes. The results of gas permeability tests for the synthesized membranes specify that using a higher percentage of polysulfone (PSF) in blends resulted in membranes with higher ideal selectivity and permeability. Although the addition of nanotubes can increase the permeability of gases, it decreases gas pair selectivity. Furthermore, these outcomes suggest that Kapton–PSF membranes with higher PSF are special candidates for CO₂/CH₄ separation compared to CO₂/N₂ and O₂/N₂ separation. High CH₄, CO₂, N₂, and O₂ permeabilities of 0.35, 6.2, 0.34, and 1.15 bar, respectively, are obtained for the developed Kapton–PSF membranes (25/75%) with the highest percentage of carbon nanotubes (8%), whose values are the highest among all the resultant membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43839.     

Improved adhesion between Kapton film and copper metal by silane-coupling reactions

Kapton film, poly[(N,N′-oxydiphenylene)pyromellitimide], was modified by silane-coupling reactions using 3′(trimethoxysilyl)propoxy-2-hydroxypro-pyl-1,3-diazole (Si–imidazole) to improve the adhesion with copper metal. The Kapton film surface was first treated with argon plasma for 30 s, then dipped into a methanol solution of Si–imidazole (0.01 wt %), followed by heating at 110°C for 90 min. The Kapton surfaces, modified by the argon plasma and Si–imizadole coupling reactions, were analyzed by water contact-angle measurement, atomic force microscopy, and XPS. The Si–imidazole modification showed a large increase in adhesion between the copper metal and the Kapton film. The peel strength of the copper metal/Kapton film joint increased from 0.94 to 2.4 N/5 mm. The failure occurred at the interface between the Si–imidazole and the Kapton film layer. We conclude that the Si–imidazole modification is an effective treatment for improvement of the adhesion between copper metal and Kapton film. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1645–1654, 1999     

Preparation and properties of some poly(alpha-olefin sulfones)

The properties of alpha-olefin–sulfur dioxide copolymer prepared from the series C₈–C₁₈ (even-numbered) alpha-olefins and sulfur dioxide are described. These polymers undergo clean thermal degradation and have high permeabilities to oxygen and carbon dioxide. Maximum permeabilities, maximum per cent elongation at the yield point, and minimum density are obtained with the C₁₆-based polymer. An explanation is proposed involving a competitive plasticizing/side chain crystallization effect.     

The permeability of gases through reacting solutions: the carbon dioxide—bicarbonate membrane system

The transport of a gas across a stationary liquid film containing reactive species is investigated for the purpose of determining gas permeabilities or mass transfer coefficients in reacting solutions. Under limiting conditions when the reaction time constant far exceeds the diffusional time constant, the flux of the transported gas follows Fick's law of diffusion. Analytical series solution for the contribution of the chemical reaction to the transport process is obtained using the technique of perturbation analysis; criteria for the validity of various terms in the series solution are presented. The permeability of carbon dioxide in water and in 1N NaHCO₃?Na₂CO₃ solution is estimated. It is shown that a high degree of accuracy in the data is necessary for obtaining separate estimates of diffusivity and solubility by this technique.     

High-pressure phase behavior of carbon dioxide in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Phase equilibrium data of carbon dioxide in the ionic liquid 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]) are presented at high pressures up to about 30 MPa and at temperatures between 298.15 K and 343.15 K. The solubilities at a given temperature were determined by measuring the bubble point pressure of the ionic liquid solution with carbon dioxide dissolved using the high-pressure equilibrium apparatus equipped with a variable-volume view cell. Solubility results are reported for carbon dioxide concentrations ranging from 0.21 up to 0.80 mole fraction. Carbon dioxide gave very high solubilities in the ionic liquid at lower pressures, while the equilibrium pressure increased very steeply at higher concentrations of carbon dioxide. The solubility of carbon dioxide in the ionic liquid decreased with an increase in temperature.     

Determining the carbon dioxide permeability of paint films

An in-house set-up was developed for determining the permeability of, paint films towards carbon dioxide. The system implemented the so-called Wicke-Kallenback method, described in EN 1062-6. This method consists of a two-chamber permeation cell divided by a supported paint film. A carbon dioxide/nitrogen mixture stream (15% CO₂/85% N₂) is fed to the retentate chamber and a nitrogen carrier stream is fed to the permeate chamber. Carbon dioxide permeates from the retentate to the permeate chamber. The carbon dioxide flow rate is obtained from the permeate concentration and flow rate. From the carbon dioxide flow rate it is possible to calculate the paint film permeability towards this gas. The coating system is applied on a Kraft paper support sheet; the Kraft paper by itself shows negligible permeation, resistance. Coatings to be considered as “surface protection systems for concrete” must comply with EN 1504-2. This standard requires that the paint film permeability have an equivalent air thickness of S_D≥50 m. The unit developed was able to quickly determine permeabilities as low as an equivalent air thickness of S_D=1500 m.     

The high resolution 13C NMR spectrum of poly(N,N′-bis(phenoxyphenyl) pyromellitimide), (Kapton)

Summary The high resolution ¹³C NMR spectrum of Kapton in sulfuric acid solution is reported. Assignments to the spectrum were made by comparison with non-proton-decoupled spectra, and with improved solid-state spectra. The solid-state spectrum of the reprecipitate from a H₂SO₄ solution showed that no change in the chemical structure of Kapton occurred during dissolution, but that the regular morphology present in the original film had been disrupted.     

Characterization of penetrant interactions in Kapton polyimide using a gravimetric sorption technique

Sorption of pure anhydrous ammonia and pure sulfur dioxide in Kapton polymide has been measured at 30 and 35°C at subatmospheric pressures using a McBain quartz spring balance. The sulfur dioxide sorption and desorption was well described by the Fickian transport model; however, the ammonia sorption exhibited significant deviations from Fickian behavior. A substantial fraction of the initially sorbed ammonia remained in the film after extended periods under vacuum at 35°C. Infrared analysis of the treated film revealed the presence of new carbonyl and nitrogen–hydrogen stretching peaks characteristic of primary and secondary amides. These observations suggest that the ammonia reacts chemically with some of the imide linkages. Based on infrared analysis of the ammonia-exposed Kapton, heating the sample under vacuum at 120°C caused re-formation of most of the orginally disturbed imide structures, with attendant evolution of ammonia as a condensation product.     

Temperature effects on permeation of modified atmosphere gas mixtures through a low density polyethylene package film

Permeation of CO₂ and O₂ through a low density polyethylene film was studied with CO₂-N₂ mixtures in the temperature range 263-283 K, and with CO₂-O₂-N₂ mixtures in the range 257-313 K. The temperature dependence of the permeabilities of these gases agreed with the Arrhenius expression. The activation energy for carbon dioxide diffusion was between 3.53 × 10⁴ and 3.74 × 10⁴J/mol; the activation energy for oxygen diffusion was 3.13 × 10⁴J/mol. The pre-exponential constant for oxygen was higher than that of carbon dioxide in various mixtures. It was also found that the pre-exponential constant of carbon dioxide decreased with increasing CO₂ concentration in the mixtures.     

Solubilities of solids in supercritical fluids

The solubilities of several low-volatility compounds in supercritical fluids were measured. The fluids used were pure carbon dioxide or carbon dioxide modified with small amounts of organic liquids. Some enthalpies of solution of solids in carbon dioxide at a density of 0.80 g/mL are presented. The enthalpy of solution of fluoranthene in carbon dioxide was found to be less endothermic at higher CO₂ density. The order of solubilities in the modified fluids was the same as that in the pure liquid modifiers. The same apparatus was used to measure vapor pressures of some substances as well as solubilities.     

Synthesis of carbon nanosheets from Kapton polyimide by microwave plasma treatment

Vertically-aligned carbon nanosheets (CNSs) have been fabricated on the Cu substrate from Kapton polyimide (PI) film under Ar/H₂ plasma irradiation. The high purity CNSs possess petal-like structures with many sharp edges, which are composed of few-layer graphene sheets. In addition, the irradiated Kapton PI film was covered by a layer of urchin-like carbon particles with about 4 μm in diameter, which also consist of few-layer graphene sheets along radial directions. Except for the morphologies, both the CNSs and urchin-like carbon particles demonstrate similar microstructures and chemical compositions.     

The solubility of sulfur dioxide and hydrogen sulfide in associating solvents

The solubilities of SO₂ are reported in the solvents N, N-dimethyl acetamide (DMA), N, N-dimethyl formamide (DMF), ethyl acetate, acetonitrile, chlorobenzene, methanol, (1,2-ethanediol) ethylene glycol and acetone for atmospheric pressure and for temperatures ranging from 268 K to 333 K (-5°C to 60°C). Solubilities of H₂S are also reported for the first five of the above-mentioned solvents and for hexane for similar conditions. These gases and solvents exhibit extreme molecular interactions which are reflected in unusual solubility behavior. This paper is a continuing attempt in providing data and analyses for improving the understanding of gas solubilities in complex gas-solvent systems. Solubilities expressed as hydrogen-bonding factors have been found useful in systematically relating gas solubilities in one associating or reacting solvent to another chemically similar solvent. Thus, with a limited amount of data for gas solubilities, it is often possible to predict solubilities even in highly associated or reacting gas-solvent solutions.     

Gas Separation Properties of Phosphazene Polymer Membranes

Abstract

In this paper the gas separation properties of poly[bis(phenoxy)phosphazene] are reported. Transport behavior was determined by time-lag techniques and correlated with membrane microstructural studies. Test gases were run as pure or single-species gases, which included atmospheric gases, hydrocarbons, sulfur dioxide, and hydrogen sulfide. Transport of atmospheric and hydrocarbon gases was found to be a diffusion controlled processr; i.e., correlated with molecular size. Transport of CO₂, H₂S, and SO₂ was found to be a sorption controlled process since high solubilities were measured and transport deviated from the diffusion controlled permeability-size correlation. Membranes were prepared using spin and knife casting techniques. Solvent evaporation rate during the casting process was used to provide different membrane microstructures. Rapid evaporation by spin casting resulted in dense homogeneous films, with permeabilities ranging from 2–6 barrers for the slowest (Ar) to fastest gases (He). Slow evaporation by knife casting (minutes-hours) resulted in a more open polymer structure. Two enhancement effects were observed in the transport behavior of the knife-cast membrane: 1) an overall increase in permeability for all gases depicting the more open membrane structure (ranged from 4–76 barrers for all gases) and 2) an enhancement of the selectivity of gases which exhibited strong solubility effects. Sulfur dioxide and hydrogen sulfide exhibited the greatest selectivity enhancements. The pure gas solubility selectivities for S0₂ and H₂S with respect to the atmospheric and hydrocarbon gases were found to be approximately 1000 and 200 respectively.     

Prediction of solubilities of solid solutes in carbon dioxide-expanded organic solvents using the predictive Soave–Redlich–Kwong (PSRK) equation of state

In this study, the solubilities of solid solutes in carbon dioxide (CO₂)-expanded organic solvents are predicted using the predictive Soave–Redlich–Kwong (PSRK) equation of state (EOS). The liquid-phase compositions and volume expansion ratios of CO₂-expanded organic solvents are predicted prior to the solubility predictions. With predicted liquid-phase compositions and volumetric properties, the solubilities of cholesterol in CO₂-expanded acetone, naphthalene in CO₂-expanded toluene, stearic acid in CO₂ expanded ethyl acetate and tetradecanoic acid in CO₂-expanded ethyl acetate are predicted according to their reference solubilities in pure organic solvents. In addition to satisfactory predictions of liquid-phase composition and volume expansion ratios, the PSRK EOS also provides qualitative prediction ability for solubilities of solid solutes in CO₂-expanded organic solvent. This study demonstrated that the PSRK EOS was a simple model with predictive ability for solubility evaluation in preliminary process design and development for supercritical fluid technology using CO₂-expanded organic solvents.     

The anodic characteristics of manganese dioxide electrodes prepared by thermal decomposition of manganese nitrate

Manganese dioxide electrodes were prepared by a thermal decomposition of manganese nitrate solution on a titanium or a platinum substrate, and their anodic characteristics were investigated mainly in 1N H₂SO₄ and 1N KOH. The platinum-supported manganese dioxide electrode shows the good anodic characteristics with a relatively low overvoltage for oxygen evolution while the use of the titanium-supported one as an anode needs further modification to reduce its high resistivity resulting from the thick film of titanium dioxide in spite of good adhesion of the oxide film with the titanium substrate.The primary water or hydroxide ion discharge step is rate-controlling in the anodic evolution of oxygen on the platinum-supported manganese dioxide electrode in both acidic and alkaline solutions. The oxygen overvoltage is raised and the mechanical strength of the catalytic oxide on the platinum substrate is weakened by the anodic polarization in acidic solution. These phenomena are explicable on the basis of an increase in the oxygen content in the oxide. In conclusion, the presented results suggest that the manganese dioxide film is a practical usable material for the anodic evolution of oxygen as well as chlorine, especially in alkaline solutions.     

Solubility of simple and mixed triacylglycerols in supercritical CO2

A simple mixture of triacylglycerols (TAGs) was synthesized enzymatically from palmitic acid and oleic acid. The mixture contained tripalmitoylglycerol (PPP), trioleoylglycerol (OOO), and various isomers of palmitoyl-dioleoylglycerol (POO) and oleoyl-dipalmitoylglycerol (PPO). The behavior of this TAG mixture in equilibrium with supercritical carbon dioxide (SF-CO₂) was studied at 40 and 60°C between 172 and 310 bar. Generally, the partition coefficients varied inversely with species molecular weight. The solubilities of PPP and OOO in SF-CO₂ were determined at the same conditions. PPP was markedly more soluble in SF-CO₂ when present in the TAG mixture than as a pure compound.     

Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation

A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N₂/CH₄ permeation tests. The effects of final pyrolysis temperature on N₂/CH₄ separation are reported. The separation performance of all CMS dense films significantly exceeds the polymer precursor dense film. The CMS dense film pyrolyzed at 800 °C shows very attractive separation performance that surpasses the polymer membrane upper bound line, with N₂ permeability of 6.8 Barrers and N₂/CH₄ permselectivity of 7.7 from pure gas permeation, and N₂ permeability of 5.2 Barrers and N₂/CH₄ permselectivity of 6.0 from mixed gas permeation. The temperature dependences of permeabilities, sorption coefficients, and diffusion coefficients of the membrane were studied, and the activation energy for permeation and diffusion, as well as the apparent heats of sorption are reported. The high permselectivity of this dense film is shown to arise from a significant entropic contribution in the diffusion selectivity. The study shows that the rigid ‘slit-shaped’ CMS pore structure can enable a strong molecular sieving effect to effectively distinguish the size and shape difference between N₂ and CH₄.     

Hyperbranched poly(glycerol esteramide): A biocompatible drug carrier from glycerol feedstock and dicarboxylic acid

Polymer carrier with biodegradable, biocompatible as well as solubility enhancing properties are highly looked upon in the pharmaceutical industry to improve the drug delivery systems. A series of hyperbranched poly(glycerol esteramide) (HPGEA) with M_w of 5000–12,000 Da, degree of branching of 57%–62%, and hydroxyl values of 200–280 mg KOH/g sample were synthesized through polycondensation of N,N-bis(2-hydroxyethyl)stearamide (diethanolamide) and poly(glycerol ester) (PGE). The HPGEAs were characterized by ATR-FTIR, GPC, ¹H and ¹³C-NMR, and DSC. The enthalpy of fusion of HPGEAs (43–84 J g⁻¹) were lower than the commercial polymers (193–391 J g⁻¹), indicating its potential as drug carrier for solid dispersion (SD). HPGEA-based SDs showed substantial enhancement in solubility and release rate than pure drug, commercial polymer-based SDs, as well as commercial formulation. The safety of HPGEAs and HPGEA-based SDs were proven through MTT assay with IC₅₀ of 2400–9800 and 1200–3500 μg ml⁻¹, respectively.     

Diffusion and sorption for carbon dioxide in Kapton at extremely low pressure

Pressure-dependent solubility and diffusion coefficients for carbon dioxide in glassy polymers have been well described using the “dual sorption and transport model.” However, the plastisization effect by high-pressure carbon dioxide seems to promote the pressure dependence of the sorption and transport coefficients. To avoid the relaxation process by the plastization which is superimposed on the diffusion process, the diffusion and sorption of carbon dioxide were measured at extremely low pressure (below 1 cmHg). Linear isotherms observed for CO₂ sorption into Kapton were interpreted in terms of the dual model equation at extremely low pressure. From the permeation curve of the Kapton/CO₂ system, the diffusion and permeation coefficients were obtained according to the usual manner, and both coefficients were independent of pressure. Sorption and transport parameters were obtained from sorption isotherms and average values of the permeation coefficients. The parameters thus obtained were substituted in an approximated dual sorption and transport equations at extremely low pressure and the pressure independence of the diffusion and permeation coefficients were sufficiently reproduced. It is a good technique to experiment at such extremely low pressure when the validity of the dual model is evaluated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1013–1017, 1998     

Synthesis of soluble oligsiloxane-end-capped hyperbranched polyazomethine and their application to CO2/N2 separation membranes

Three soluble hyperbranched polyazomethines containing oligosiloxane end group HBP-PAZ-SiO_n were successfully synthesized. HBP-PAZ-SiO_ns were used as modifiers of ethyl cellulose (EC) and polysulfone (PS) membranes. Blend membranes, HBP-PAZ-SiO_n/EC and HBP-PAZ-SiO_n/PS were prepared by blending the THF solution of HBP-PAZ-SiO_n with ethanol solution of EC and dichloromethane solution of PS, respectively. Surprisingly, the permeabilities for CO₂ of the blend membranes were more than 15–16 times higher than those of pure EC and PS membranes without any drop of pemselectivity to N₂. This unusual improvement has been achieved by both enhancement of diffusivity for carbon dioxide and nitrogen by the oligosiloxane groups and enhancement of affinity of the amino groups with carbon dioxide at the end groups of HBP-PAZ-SiO_n.