Permeability of oxygen and nitrogen gases in ethyl cellulose solid films retaining cholesteric liquid crystalline order

Ethyl cellulose (EC) films that retain lyotropic and thermotropic cholesteric liquid crystalline order, and an amorphous EC film were prepared. The liquid crystalline order was identified by optical measurements. The comparative permeability of oxygen and nitrogen gases for three kinds of EC film was determined, and the applicability of the EC films that retained cholesteric liquid crystalline order to oxygen enrichment are discussed. The permeability of oxygen or nitrogen gas for the liquid crystalline films was lower than that for the amorphous ones. The activation energy for the permeability coefficient of oxygen gas was ca. 3.5 kcal/mol. The ratio of permeability coefficient for oxygen gas to that for nitrogen gas was less than 4. Interestingly, the permselectivity of oxygen and nitrogen gases for the liquid crystalline films was greater than that for the amorphous ones. © 1996 John Wiley & Sons, Inc.     

Gas permselectivity properties of high free volume polymers modified by a low molecular weight additive

The permselectivity properties of mixtures of the highly substituted polymers tetramethylhexafluoro polysulfone (TMHFPSF) and tetramethylhexafluoro bisphenol A t-butyl isophthalate (TMHFBPA-tBIA) with a low molecular weight glassy additive Kenflex A (denoted here as KXA) were measured for different gases and compared with the permselectivity properties shown by the base, unsubstituted polymers polysulfone (PSF) and bisphenol A t-butyl isophthalate (BPA-tBIA). The results show that the selectivity-permeability balance of polymer membranes may be appropriately tailored by a combination of chemical and physical alterations of the base polymer. The addition of modest amounts of KXA (ca. 20 wt %) into TMHFPSF or TMHFBPA-tBIA leads to materials whose permeability/selectivity combination is better than that of the unsubstituted materials, PSF or BPA-tBIA. The polymer TMHFPSF responds more beneficially to the incorporation of KXA than TMHFBPA-tBIA. At the same level of permeability, mixtures based on TMHFPSF have higher selectivity factors for H₂/CH₄ and CO₂/CH₄ than those based on TMHFBPA-tBIA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 403–415, 1998     

Static tensile and dynamic mechanical properties of hydroxypropylcellulose films prepared under various conditions

The films of hydroxypropyl cellulose (HPC), which is a lyotropic and thermotropic liquid crystal, were cast under various conditions of temperature and concentration. The effects of the casting conditions on the static tensile and dynamic mechanical properties of the cast films were determined, and the results were compared with those of films prepared by means of hot compression. The tensile properties of the films prepared by both processes (cast and hot compression) were unsatisfactory in comparison with other liquid crystalline polymers, and this was partly due to water absorbed during the test. In dynamic properties, two distinct transitions were detected. The higher one, around 110°C, was associated with the rotation of an unhydroglucose ring and the lower one, around 25°C, was associated with the T_g. There were no marked differences in the properties between cast films and hot-compressed films, except the disappearance of the T_g for hot-compressed film prepared at a relatively higher temperature. The basis for defining the liquid crystalline structure in cast and hot-compressed films are not directly given in this preliminary paper. However, judging from the dynamic mechanical properties and refractive index data for films prepared by both processes, it appears that dimethylacetamide-cast films and films compressed at 180 and 200°C may have some structures related to liquid crystalline phase and that inter- and intramolecular hydrogen bonding play an important role in lyotropic and thermotropic liquid crystalline behavior for HPC.     

Characterization and transport properties of a novel aliphatic polyamide with an ethyl branch

The CO₂ gas and water vapor transport properties of a novel aliphatic polyamide with an ethyl branch were investigated. The polymer was characterized with density measurements, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction analyses, and the amorphous and glassy nature of the polymer at the ambient temperature were confirmed. The CO₂ sorption isotherm of the polymer appeared to obey the dual‐mode sorption isotherm, which was characteristic of the glassy state. The water vapor sorption below a relative humidity of 0.4 or 0.5 was explained in terms of the Brunauer–Emmett–Teller sorption mechanism, whereas that at a high relative humidity demonstrated a dissolution type of water vapor into the polyamide. The permeability coefficients of He, CO₂, O₂, and N₂ gases through the membrane were as follows: P(He) > P(CO₂) > P(O₂) > P(N₂). The novel polyamide membrane was more permeable to CO₂, O₂, and N₂ gases than nylon 6 and nylon 66 membranes, containing a crystalline and hydrogen‐bonding nature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1955–1960, 2005     

Temperature dependency of gas barrier properties of biodegradable PP/PLA/nanoclay films: Experimental analyses with a molecular dynamics simulation approach

Polypropylene (PP)/poly(lactic acid) (PLA)/clay nanocomposite films with various compositions (PP‐rich and PLA‐rich) were prepared. Their structural and barrier properties against CO₂, O₂, and N₂ were investigated. The microstructure of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy, and wide angle X‐ray scattering. The PP‐rich with 75/25 composition revealed the best barrier properties against all the gases which could be justified according to its microstructure. Selectivity of O₂/N₂ and CO₂/N₂ was also measured. It was found that the addition of nanoclay as a gas barrier component reduced the permeability in both systems. The permselectivity was also reduced in the PP‐rich films while it was increased in the PLA‐rich system. Moreover, the temperature dependency of permeability, selectivity, and permselectivity for PP, PLA, and PP/PLA (75/25) samples was examined. The results showed that the temperature dependence of permeability obeyed an Arrhenius equation and order of activation energy of permeability for O₂, CO₂, and N₂ gases was found to be E_P < E_P/PLA < E_PLA. According to solubility measurements, the order of solubility coefficient for gases was as follows: CO₂ > O₂ > N₂. Finally, the molecular dynamics (MD) simulation was performed to estimate the diffusivity coefficients of the gases and showed that solubility increases with increasing temperature, which was in accordance with the experiments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46665.     

Permeability of dried gases and gases dissolved in water through polyimide membranes modified by immersing in amino compound solutions

Membranes of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA)?2,3,5,6‐tetramethyl‐1,4‐phenylene diamine (TeMPD) polyimide, a fluorine‐containing polyimide synthesized using 6FDA and TeMPD, were modified by immersing them in various amino compound solutions for application in artificial lungs. Permeabilities of dried gases (P_G) and gases dissolved in water (P_L) through the membranes were investigated. The surface reaction ratios of all the modified membranes were higher than the total reaction ratio, indicating that the modified membranes exhibited graded structures that were reacted with amino compounds from both surfaces toward the interior. Both P_L (O₂) and P_L (CO₂) of the base membrane and amine‐modified membranes, except the membrane where d ‐glucamine was used, were lower than or equal to P_G (O₂) and P_G (CO₂), respectively. Both P_L (O₂) and P_L (CO₂) of the amine‐modified membranes decreased with increasing water content, which suggests that water content strongly affected permeability in liquid phase. Results indicate that water molecules interrupted gas permeation. Moreover, CO₂/O₂ permselectivity in liquid phase increases with high‐polarity amino compounds compared with the base membrane. POLYM. ENG. SCI. 56:178–186, 2016. © 2015 Society of Plastics Engineers     

Characterization of Nanocomposite Polymeric Membrane

Composite membrane has good permeability and selectivity for gases, which depends upon the operating conditions. The solubility and diffusivity of the penetrant in the polymer matrix control the transport through non-porous dense membrane. In the present work, the nano sized particles of Co_0.6Zn_0.4Fe₂O₄ were prepared by the co-precipitation method and characterized by the XRD technique with particle size of 10 nm. Nanocomposite polycarbonate membranes were studied before and after irradiation by the ³⁵Cl⁹⁺ ion of 120 MeV at the Nuclear Science Centre, New Delhi. The distribution of nanoparticles throughout the membrane was characterized by the optical microscope. Gas transport properties of H₂, CO₂ and air for these nanocomposite membranes were investigated. It was found that membrane containing nanoparticles shows low permeability with high permselectivity. After irradiation by swift heavy ions (SHI), high gas permeability and high permselectivity has been observed for these nanocomposite membranes.     

Effect of the thermal treatment of ionomer films on permeability and permselectivity

Ionomers have been studied in detail and have gained widespread commercial use. Interested in altering the ratio of CO₂/O₂ permeability (i.e., permselectivity) of films for use in packaging respiring produce, we pressed sodium‐neutralized poly(ethylene methacrylic acid) ionomers into films at 120–160°C and investigated their thermal, morphological, and permeability properties. The heat treatment of the ionomers at 160°C increased the gas permeability for O₂ more than for CO₂ and reduced the CO₂/O₂ permselectivity ratio from 4.1 to 1.6. The reasons for these changes in the permeability characteristics of the ionomers are not understood but could be related to a reduction in the polyethylene (PE) crystallinity and the destruction of the aggregates into smaller, dispersed clusters. These results were supported by differential scanning calorimetry data and scanning electron micrographs. This suggests that the heat treatment of ethylene–methacyrlic ionomers may improve their potential for applications as selective barriers for modified‐atmosphere packaging of respiring produce. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2811–2815, 2002     

Gas permeabilities of cellulose nitrate/poly(ethylene glycol) blend membranes

The permeability (P) of cellulose nitrate (CN)/poly(ethylene glycol) (PEG) blend membranes for N₂, O₂, and CO₂ has been measured as a function of film composition. The system CN/PEG-300 showed excellent miscibility, and films of the composition from 100/0 to 50/50 could be used for permeability measurements. P for each gas has been found to be almost constant or rather slightly lowered up to ca. 20 wt % PEG-300 content and then increased appreciably with increasing fraction of PEG. The increment of permeability was most remarkable for CO₂, and hence the permselectivity for CO₂ was considerably enhanced. Such a behavior of P has been found to be attributable to the plasticizing effect of PEG molecule lowering the glass transition temperature of the blend polymers. The effect of the molecular weight of PEG and that of closed voids generated in glassy blend membranes fabricated from acetone cast on gas permeabilities have been also discussed.     

The gas permeation properties of 6FDA-2, 4, 6-trimethyl-1, 3-phenylenediamine (TMPDA)/1, 3-phenylenediamine (mPDA) copolyimides

Summary The gas permeation behavior of 2, 2’-bis (3, 4’dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)- 2, 4, 6-Trimethyl-1, 3-phenylenediamine (TMPDA)/1,3-phenylenediamine (mPDA) polyimides was investigated by systematically varying the diamine ratios. The physical properties of the copolyimides were characterized by IR, DSC and TGA. All the copolyimides were soluble in most of the common solvents. The gas permeabilities and diffusion coefficients decreased with increasing mPDA content; however, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, CO₂/CH₄ was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to decrease with the increasing order of kinetic diameters of the penetrant gases. Moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability.     

Gas transport in poly(alkoxyphosphazenes)

The permeability of four structurally related poly(alkoxyphosphazenes), three isomers of poly(dibutoxyphosphazenes) (PBuP), and poly(di-neopentyloxyphosphazene) (Pneo-PeP), to 13 gases has been determined by the time-lag method. Systematic variations in chemical structure have shown a large effect of side chains on permeabilities and permselectivities. The permeability of poly(di-n-butoxyphosphazene) (Pn-BuP) is of the order of 10^?8 cm³ (STP) cm/(cm² s cmHg) for many gases, and the value for a large gas is higher than that for a smaller one. For small gases such as He and H₂, poly(di-sec-butoxyphosphazene) (Ps-BuP) is as permeable as Pn-BuP, but its diffusivities for larger gases such as Xe and C₃H₈ are about one order lower than those of Pn-BuP. While the permselectivity of Pn-BuP is determined by the solubility, that of Ps-BuP depends on both the diffusivity and solubility factors. The property of poly(diisobutoxyphosphazene) (Pi-BuP) is intermediate between them. These polymers are constitutionally identical, and the only difference is the arrangements of carbons in the side groups. As the side chains become bulky, the permeability decreases, whereas the permselectivity increases. Further decreases of diffusivity and then permeability are observed for Pneo-PeP, whose side groups have one more methyl group than does Pi-BuP. But the solubility data are not much different from other three polymers and the diffusivity factor becomes more significant in permselectivity. The diffusivity depends on the polymer structure much more than does the solubility. The relationships between chemical structure and gas diffusivity and solubility are discussed.     

Plasma polymerization of perfluoro-2-butyltetrahydrofuran/methane and perfluorobezene/tetrafluoromethane mixtures and gas permeation properties of the plasma polymers

Plasma polymer films prepared from perfluoro-2-butyltetrahydrofuran (PFBTHF) and perfluorobenzene (PFB) were investigated by elemental analysis, infrared spectroscopy, and ESCA. The gas separation properties were also investigated to seek plasma polymer films with good permselectivity. Plasma polymer films from PFBTHF and PFB were composed of polymer chains with fluorinated moieties such as C –CF_n, C F, C F–CF_n, C F₂, and C F₃ groups. Changes in the afcurrent as an operating condition for plasma polymerization showed less influence on the distribution of the fluorinated moieties but more influence on the permselectivity of the plasma polymer films formed. The permselectivity was improved by plasma polymerization in the PFBTHF/CH₄ or PFB/CF₄ mixture systems. The P_O2/P_N2 ratio for the plasma polymer films prepared from PFBTHF/CH₄ and PFB/CF₄ mixtures increased from 3.1 at 0 mol % CH₄ to 4.0 at 50 mol % CH₄ addition, and from 4.1 at 0 mol % CF₄ to 5.0 at 25 mol % CF₄ addition, respectively. The permselectivity of the plasma polymer films may be related to the crosslinkage and aggregation of polymer chains rather than the elemental composition.     

Structure/permeability and permselectivity relationship of polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride. I

Gas permeability coefficients of a series of aromatic polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and various aromatic diamines, to H₂, CO₂, O₂, N₂ and CH₄ have been measured under 7 atm pressure and over the temperature range 30–150°C. A significant change in permeability and permselectivity, which resulted from a systematic variation in chemical structure of the polyetherimides, was found. Generally, increases in permeability of the polyetherimides are accompanied by decreases in permselectivity. The order of decrease of the permeability coefficients is as follows: HQDPA–IPDA > HQDPA–DDS > HQDPA–MDA > HQDPA–ODA > HQDPA–DABP > HQDPA–BZD. However, HQDPA–DMoBZD and HQDPA–DMoMDA, with bulky methoxy side-groups on the aromatic rings of the diamine residue, display both high permeability coefficients and high permselectivity. The favourable gas separation property, excellent thermal and chemical stability, and high mechanical strength make HQDPA–DMoBZD and HQDPA–DMoMDA promising candidates for membrane-based gas separation applications.     

Swelling behavior of crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effect of temperature

Temperature dependence of the swelling behavior in both water and propanol was determined for the crosslinked hydroxypropyl cellulose (HPC) films retaining cholesteric liquid crystalline order (CLCO) and for the crosslinked amorphous HPC films. The dependence of swelling behavior in water for the films retaining CLCO was different from that of the amorphous films. With increasing temperature, the equilibrium swelling ratio (B_e) for the films retaining CLCO decreased, whereas B_e for the amorphous films increased. In propanol, both films exhibited the same temperature dependence. B_e increased with increasing temperature. The increasing rate of the swelling in transient state showed similar temperature dependence on B_e. The increasing rate for the films retaining CLCO decreased with temperature, but that for the amorphous films increased in water; in propanol, the increasing rate for two types of films increased. The difference in the swelling behavior between the two types of films may be due to the difference in the number-average molecular weight between crosslinks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1015–1022, 1999     

Separation of SF6 from Binary Mixtures with N2 Using Commercial Poly(4-Methyl-1-Pentene) Films

Systematic studies on gas permeation of pure SF₆ and N₂ as well as their mixture in poly(4-methyl-1-pentene) (PMP) at different temperatures and pressures, using commercially available thin PMP films, are reported in this article. The effective separation of SF₆ from binary mixtures with N₂ is critical for the proposed replacement of pure SF₆, used as an insulating gas in high power industry, by the mixtures of these two gases. This replacement is driven by the fact that SF₆ is the most potent greenhouse gas, with a global warming potential of 22,200 times that of CO_2. The experiments with a 1:1 mixture of N₂ and SF₆ revealed the permselectivity of PMP as high as 476 with the corresponding N₂ permeability coefficient of 7.6 Barrer. These properties, which are much better than those of other glassy polymers considered for this separation, were not affected by a long-term exposure to SF₆, which indicates the excellent resistance of PMP to plasticization by this gas. Using a single stage membrane system utilizing the PMP membrane would allow separating the above gas mixture into a 99% pure SF₆ product with the corresponding recovery rate of SF₆ greater than 99%.     

Barrier properties of a thermotropic liquid‐crystalline polymer

A developmental thermotropic liquid‐crystalline polymer (TLCP) made by Eastman (trade name LN001) was used for barrier property studies. This material is a highly aromatic TLCP with a T_m of 332°C. A permeability study was carried out to determine the chemical resistance of the TLCP. The permeability of methanol and toluene through a membrane of the TLCP was studied using a two‐part cell and a gas chromatograph to monitor the flux. The membranes of the TLCP and LDPE (as control) were made by compression molding. Both solvents had higher permeability through LDPE than TLCP and that of toluene was higher than that of methanol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2457–2463, 2003     

Gas sorption and transport in UV-irradiated poly(2,6-dimethyl-1,4-phenylene oxide) films

Gas sorption and transport properties at 35°C have been reported for a series of UV-irradiated films of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). UV irradiation induced crosslinking in all films. The gas permeability was reduced upon crosslinking while significant increases in gas permselectivity were observed. The addition of benzophenone to the PPO films did not result in marked improvements in crosslinking or the resulting gas transport properties of the film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:875–883, 1998     

Synthesis and characteristics of HAB-6FDA thermally rearranged polyimide nanocomposite membranes

The thermal rearrangement of polyimides of ortho-positioned functional group membranes improves the gas permselectivity properties of the polyimide precursor. For this experiment, HAB-6FDA polyimide was synthesized from 3,3 dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) by chemical imidization. A sample was modified from a pure polymer to silica nanoparticle composition. Furthermore, a modification was carried out by thermal rearrangement reaction at temperatures of 350, 400, and 450°C. The thermal property of these membrane films was characterized by differential scanning calorimetry (DSC), FTIR, opacity experiment, and free volume analysis. Permeability decreases with an increase in the kinetic diameter of gasses, which is normal behavior for glassy polymers. The composition of silica nanoparticles slightly changes the permeability in the polyimide. The combined effect of silica nanoparticles and thermal rearrangement of the HAB-6FDA membrane has shown an excellent performance. The thermal rearrangement with nanocomposite shows a significant impact on a larger effect on permeation for lighter gases, that is, H₂, CO₂, and O₂, compared with N₂ and CH₄. Particularly for H₂/CH₄ gas pair, it lies over Robeson's 2008 upper bound limit, which fits the composition in the novel class for the gas separation membranes.     

Toluene vapor removal using an inorganic/organic double-network ion gel membrane

ABSTRACT

Tough gel membrane composed of a large amount of an ionic liquid and an inorganic/organic composite double-network (inorganic/organic DN ion gel membrane) was examined to remove toluene vapor from toluene vapor/N₂ mixed gas. The DN ion gel membrane with 80 wt% of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide showed higher toluene vapor permeability (more than 30,000 barrer) and toluene vapor/N₂ permselectivity (690) than the supported ionic liquid membrane. The toluene vapor permeability and toluene vapor/N₂ permselectivity were maintained under pressurized condition. It was confirmed that the toluene vapor permeation was limited by intramembrane diffusion of the dissolved toluene vapor.     

Effects of mechanical drawing on gas transport in an emulsion acrylic multipolymer

A study was conducted on the gas sorption and transport properties of a multiphase commercial acrylic polymer trade-named Korad ACV before and after subjecting the polymer to mechanical drawing operations. The Korad system is an emulsion-polymerized amorphous composite comprised of a glassy, predominantly PMMA matrix phase and a ply(butyl acrylate)-dispersed phase surrounded by a PMMA/PBA copolymer shell. Large increases (up to eightfold) in permeability P to several gases were observed upon drawing Korad. The observed changes in the permeability to He, Ar, N₂, and CH₄ on drawing were correlated with the draw ratio, drawing temperature, and molecular diameter of the gas penetrant. Most of the increase in permeability occurred at low draw ratios (1–2). The increases in P were most dramatic for drawing temperatures below or near the T_g of the matrix phase (about 90°C) and were quite small for drawing temperatures 30°C or more above the matrix T_g. The extent of the permeability increase also depended on the gas, being greatest for CH₄ and essentially imperceptible for He. The changes in permeability behavior were interpreted in terms of a morphological transformation in the phase of the drawn Korad, which causes the originally dispersed rubber particles to assume a more continuous character. The behavior of the composite was modeled by the Takayanagi and Nielson treatments of two-phase composite systems. Volumetric, thermal, mechanical, and viscoelastic properties were measured for the as-received and processed Korad films to elucidate physical changes in the drawn polymer.