Development of polyimide membranes for the separation of water vapor from organic compounds

Attempts were made to develop solvent‐resistant polyimide capillary membranes with integrally skinned asymmetric structure to be used for the treatment of wood dryer emissions or vacuum pyrolysis aqueous effluents. Model mixtures of 1‐propanol (1‐PrOH)/H₂O and acetic acid (AA)/ H₂O, with concentrations of 10–90 wt % of organic components, were used as vaporous feeds. Solvent‐resistant membranes with good mechanical and excellent vapor separation properties were prepared from polyimides based on PMDA and BPDA by the dry/wet phase‐inversion technique. Molecular structure largely influences membrane properties. For the asymmetric polyimide membranes studied, a tendency similar to that of homogeneous dense membrane was found. Membranes prepared from polyimides with diamine and dianhydride moieties, both containing rigid backbone and aromatic rings, displayed higher permeability and selectivity. Test conditions exhibited influences on membrane separation performance. Membranes prepared from copolyimide BPDA–50DDS/50ODA and PMDA–50DDS/50ODA exhibited the best mechanical and chemical properties as well as water vapor separation properties, which are considered to be of practical usefulness for applications of these membranes in the removal of water from water/organic mixtures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 139–152, 2002     

Characterization and water vapor sorption property of ABA‐type triblock copolymers derived from polyimide and poly(methyl methacrylate)

The characterization of ABA‐type triblock copolymer films derived from polyimide (PI) macroinitiator and poly(methyl methacrylate) (PMMA) synthesized by atom transfer radical polymerization was investigated by focusing on different block lengths of PMMA. The hydrophobic property tends to increase with increasing PMMA content in the triblock copolymers, while the PMMA blocks enhance the charge transfer interaction between the PI segments. The water vapor sorption measurement of triblock copolymers was determined at 35 °C. The water vapor solubility of triblock copolymers tends to decrease with increasing PMMA content. In addition, linear correlations were observed between the solubility and polymer‐free volume and polymer molecular polarity in triblock copolymers as well as in other conventional polymer families. According to Zimm?Lundberg analysis, the PMMA block segments in the triblock copolymers accelerate water vapor clustering due to the high mobility of PMMA. The mobility of PMMA block segments strongly affected not only physical properties but also the water vapor solubility of the triblock copolymers. The ABA triblock copolymerization composed of PI and PMMA is one of the effective ways to improve the hydrophobic property. © 2013 Society of Chemical Industry     

High-permeability fluorinated polyimide microcapsules by vapor deposition polymerization

Spherical microcapsules (∼1 mm in diameter and ∼1 μm in wall thickness) to be used as inertial confinement fusion targets were prepared from 6FDA-ODA polyimide by vapor deposition polymerization. Compared with the previously developed PMDA-ODA polyimide microcapsules, the 6FDA-ODA microcapsules were ∼50-fold more permeable to gases including He, D₂, O₂, N₂, Ar, and Ne, considerably more transparent in the UV-visible spectrum, and of marginally lower Young's modulus, tensile strength, and elongation at break. The microcapsules possessed amorphous morphology with an amorphous d-spacing of 5.8 Å as determined by wide-angle X-ray diffraction. The cryogenic permeability of helium was measured between 133 and 295 K, and the activation energy for permeation was determined to be 12.3 kJ/mol.     

Water vapor sorption and transport in dense polyimide membranes

The sorption and transport of water vapor in five dense polyimide membranes were studied by thermogravimetry. The sorption isotherms of water vapor in the polyimides could be successfully interpreted by both the dual‐mode sorption model and the Guggenheim–Anderson–de Boer equation. The water vapor diffusion behavior was found to be nearly Fickian at higher water vapor activities, whereas non‐Fickian diffusion was observed at lower water activities. The phenomena could be well described by the mechanism of combined Fickian and time‐dependent diffusion. The diffusion coefficient and water vapor uptake in the polyimides were strongly dependent on the polymer molecular structure. Except for the polyimide prepared from 3,3′,4,4′‐diphenylsulfone tetracarboxylic dianhydride and 1,3‐bis(4‐aminophenoxy) benzene, the permeability of water vapor in the dense polyimide membranes predicted from the sorption measurement at 30°C corresponded well with the water vapor permeability measured at 85°C. Among the polyimides studied, pyromellitic dianhydride–4,4′‐diaminophenylsulfone (50 mol%)/4,4′‐oxydianiline (50 mol%) showed both high water sorption and diffusion and, therefore, high water vapor permeability, which for vapor permeation membranes is necessary for the separation of water vapor from gas streams. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2306–2317, 2003     

Separation of organic vapor from air by aromatic polyimide membranes

An attempt was made to prepare dry asymmetric membranes of aromatic polyimide material for the separation of air–organic vapor mixtures. Membrances with the permeability of organic vapor two orders of magnitude higher than that of air could be obtained. The membrane performance depends strongly on the conditions of membrane preparation. It was found that the permeability of organic vapors exhibits a strong correlation with their cohesive energy data.     

Characterization of waterborne acrylic based paint films and measurement of their water vapor permeabilities

Recently, production of waterborne coatings has increased significantly as a consequence of strict pollution regulations. Waterborne coatings are sensitive to humidity, thus, their barrier properties with respect to permeation of moisture needs to be determined. Among various coating constituents, binder represents the matrix structure and its amount relative to the amounts of pigments and fillers can significantly affect the structure, hence the barrier property of the coating. In this study, waterborne acrylic based paints applied as protective coating on interior and exterior wall of the buildings are studied. The paint samples formulated with four different binder contents by a commercial paint company are used in the experiments. We first determine unknown ingredients of the paint samples using different characterization tools and then investigate the effect of the binder content on the structure of the paint films. In addition, water vapor permeability of the paint films is measured using a permeation cell. Results show that the barrier property of the waterborne acrylic based paint films against humidity decreases with decreased binder content due to uneven distribution of the pigments, consequently, porous structure formation in the films.     

单分散聚酰亚胺微球的形貌分析和表征

研以均苯四甲酸二酐(PMDA)和4,4-二氨基二苯醚(ODA)为单体,采用反相非水乳液法制备聚酰亚胺(PI)微球.在两相比-定时,研究了复配乳化剂的浓度对PI徽球形貌及单体含量对微球粒径的影响.产物通过红外,热重(TG),扫描电镜(SEM),粒度分析手段进行表征.SEM表明:单体浓度20%,复配乳化剂含量7.88%时,...     

Water vapor permeation and compressed air dehydration performances of modified polyimide membrane

In this paper, modification of polyimide hollow fiber membrane was carried out by introduction of tetrabutylammonium naphthalenesulfonate (BAN) into the membrane matrix. Permeation performance of modified hollow fibers was investigated helps to compressed air dehydration ability across the membrane. The experimental results showed that water sorption and water vapor permeability obviously increase with increase on BAN content in modified membranes, and air dehydration performance was improved by increasing BAN in membrane and ratio of sweeping gas. Moreover, operational pressure and feed flux also impose on important effect on compressed air dehydration capability.     

Absorption of water in polyimide resins and composites

The effect of temperature, postcure, and fiber orientation on water absorption were examined for Kerimid® 723 bismaleimide resin. The effect of fiber orientation was also examined for Avimid® N and BASF X-5260. Water absorption in Kerimid® 723 was found to have an Arrhenius temperature dependence, depend on degree of postcure, and be independent of fiber orientation. BASF X-5260 water absorption was also found to be independent of fiber orientation. Avimid® N water absorption exhibited a strong dependence on fiber orientation. © 1995 John Wiley & Sons, Inc.     

Antimicrobial properties of copper plasma-modified polyethylene

Copper plasma immersion ion implantation is utilized to produce an antibacterial surface on polyethylene. XPS analysis of the plasma-treated materials reveals that a relatively large amount of copper, about 11% relative to carbon, is implanted into the near surface region. At the same time, about 3% copper is found to be also deposited on the surface. The implanted copper is observed to have the zero valence state indicating that the implanted Cu does not bind chemically with the atoms in the polymer. On the other hand, the copper atoms close to the surface are found to have the divalent state due to surface oxidation. Formation of CC bonds is also observed due to dehydrogenation following copper plasma implantation. Based on the results of atomic force microscopy and contact angle measurements, the surface hydrophilicity and roughness are not significantly altered. Our antibacterial experiments indicate that the copper implanted polyethylene exhibits excellent antibacterial effects against Escherichia coli and Staphylococcus aureus, and the effectiveness is 96.2% and 86.1%, respectively.     

高压静电纺丝法制备聚酰亚胺超细纤维无纺布膜

采用制备聚合物纳米纤维的一种简易的重要基本方法,即静电纺丝技术,以实验室合成的聚酰胺酸（PAA）溶液为纺丝溶液,采用自制静电纺丝机进行电纺得到PAA纤维无纺布膜。采用傅立叶变换红外光谱分析技术对无纺布膜的化学结构进行了表征分析;由PAA及聚酰亚胺（PI）无纺布膜的谱图吸收峰对比分析得知,纤维热酰亚胺化的程度是比较完全的;但由相应吸收峰对比分析得知,热酰亚胺化的程度并没有达到100％。     

Characterization and application of activated carbon produced by H3PO4 and water vapor activation

Activated carbons have been prepared from woody biomass birch by using various activation procedures: a) treatment with phosphoric acid and pyrolysis at 600 °C in inert atmosphere, b) the same as in (a) followed by steam activation at the same temperature and c) treatment with phosphoric acid and direct pyrolysis in a stream of water vapor at 700 °C. The surface area and the porosity of the activated carbons were strongly dependent on the treatment after impregnation with H₃PO₄ (pyrolysis in inert atmosphere, steam pyrolysis or combination of both).Activated carbon, prepared by impregnation with phosphoric acid followed by steam pyrolysis (steam activation) had highly developed porous structure and the largest surface area among all prepared carbons (iodine number 1280 mg/g and BET surface area 1360 m²/g). The adsorption capacity of this sample for Hg(II) from aqueous solution was studied in varying treatment conditions: contact time, metal ion concentration and pH. The adsorption followed Langmuir isotherms and the adsorption capacity for Hg(II) at 293 K was 160 mg/g.     

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.     

Barrier properties of plasma-modified polypropylene and polyethyleneterephthalate

Plasma treatment changes the solvent absorption and permeation as well as the swelling properties of polymers. Enchanced solvent absorption and swelling are effects of an improved solvent compatibility. The plasma introduces a large number of different groups at the polymer surface depending on the nature of the plasma. Fluorine-containing plasmas can replace hydrogen atoms of the polymer molecule with fluorine atoms. Moreover, fluorine-containing plasma polymer layers can be formed. All these processes reduce the resulting surface free energy, reduce the diffusion length of solvent molecules, and produce a barrier layer. We have studied the formation of solvent barriers by plasma fluorination and by crosslinking by ultraviolet (UV) radiation. Thin foils of polypropylene (PP) and polyethyleneterephthalate (PET) were used as substrates. CF₄, SF₆, and SOF₂ were applied as sources of fluorine atoms. Hexafluoropropene, tetrafluorethylene, and perfluorohexylethylene form plasma polymer layers on the polymer substrates. Test solvents were n-pentane, tetrachloroethylene, dimethylsulfoxide, and mixtures of n-pentane and methanol. The permeation rate of solvents through plasma-modified polymers was measured gravimetrically. Mass spectrometry was applied to analyze the permeating components of the solvent mixtures. Fluorination of surface layers by plasma-chemical (CF₄, SF₆) means considerably reduces the permeation rate of PP (95% barrier effect) and PET (100%). The preferred permeation of one component of the pentane/methanol mixture is influenced by the polarity of plasma-introduced groups at the polymer surface.     

Characterization of the imidization of the aromatic polyimide LARC-160

The polyimide resin LARC-160 was prepared from diethyl-3,3′,4,4′-benzophenone tetracarboxylate (BTDE), ethyl-5-norbornene-2,3-dicarboxylate (NE), and Jeffamine AP-22. The imidization reactions of NE and BTDE were studied by HPLC, ¹³C-NMR, and IR. NE imidizes slowly at 12°C; BTDE imidizes when the resin is heated above 100°C. Both imidization reactions proceed directly to the imide. Neither amic acid is present in significant quantities at any stage of the imidization reactions. The monomer mixture has been stored at 12°C for periods up to 14 months. The effects of resin aging at this temperature on the chemical composition of the resin monomer mixture and the imidized polymer formed on curing were investigated. Aging the resin monomer mixture has the effect of partially advancing the imidization reaction. Aging also results in the formation of slightly higher-molecular-weight polyimide chains after curing of the resin at 140 and 180°C. Bisnadimide (BNI) is observed as a major reaction product, regardless of resin age.     

Cationic grafting from plasma-modified polymer surfaces

Summary Polypropylene (PP) fibers have been surfacechlorinated by RF plasma process and used in conjunction with Et₂AlCl to initiate the cationic grafting of styrene. Although the extent of grafting was only 1.0 wt.%, the amount of grafted polystyrene completely covers the support. Grafting efficiencies were 10 – 35%. Scanning electron micrographs indicate incompatible polystyrene (PSt) sheets covering the PP fiber surfaces.Dedicated to Prof. C.I. Simionescu's 60th birthdayThe first part of this series was presented at the 26th International Symposium on Macromolecules, Mainz, FRG and appeared as Abstract BI-28 in Preprints Makro Mainz, Vol. 1, p. 448 (1979)     

Characterization of polyimide foams after exposure to extreme weathering conditions

The weathering degradation of three closely related polyimide foams was studied by X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FT-IR) spectroscopy, Raman spectroscopy, Thermogravimetric Analysis (TGA) and Thermomechanical Analysis (TMA) after exposure at the NASA Kennedy Space Center's (KSC) Beach Corrosion Site. These foams were developed by NASA Langley Research Center for applications such as cryogenic insulation, flame retardant panels and structural subcomponents. The degradative environmental conditions at the KSC corrosion site include exposure to sunlight, exposure to changes in temperature and humidity, mechanical erosion by wind and rain, and high sodium chloride content due to the close proximity of the ocean. Other possible atmospheric contaminants include hydrogen sulfide and hydrogen chloride (the latter originating with exhausts from the launching of space vehicles). The foams were studied for a total of 17 months exposure, with samples taken at 3, 9 and 17 months. Data analyses of the weathered foams showed that chemical structure and density effects were the key variables in weathering performance. The carbonyl linkage in the dianhydride of the TEEK-L series polyimide foams is the most important factor in degradation. TEEK-H series foams, which contain an ether linkage in the dianhydride, showed much less degradation or more resistance to weathering in comparison to the TEEK-L series. In the same chemical series, the lower density foams were more degraded in comparison to higher density foams.     

Thin water vapor barriers for paper

Low-pressure plasma technique was used in the deposition of thin polymeric coatings upon a filter paper. Sixteen different monomers, including aromatic and aliphatic hydrocarbons, nitriles, chlorine-containing compounds, and a silane, were used in the coatings. Most of the coatings functioned as water vapor barriers in different degrees, and the coated samples possessed wet tensile strengths anywhere from 3 to 34 times that of the untreated samples. Attenuated total reflectance infrared spectroscopy was used to study the chemical structure of the coatings.     

High-temperature vapor deposition polymerization polyimide coating for elimination of surface nano-flaws in high-strength carbon fiber

The effect of polyimide coatings on the filament tensile strength of high-strength polyacrylonitrile-based carbon fiber was studied by using dip and high-temperature vapor deposition polymerization (VDP) coating processes. Unlike a VDP on a cold substrate, high-temperature VDP has the potential to directly synthesize and isotropically deposit a polyimide, from diamine and dihydride monomers without any by-products, on a substrate heated up to 200 °C. The average filament tensile strength of the flaw-sensitive carbon fiber improved with all the polyimide coatings used. Nevertheless, for the same monomers, the high-temperature VDP coating process was advantageous for high-efficiency surface flaw healing compared to the dip-coating process, resulting in a 25% increase in the average tensile strength of the carbon fiber. These results were evident not only for the carbon fibers without artificial nano-notches but also for those with artificial notches less than 30 nm in depth. Thus, we clearly showed the potential for the VDP polyimide coating to heal surface nano-flaws of the carbon fiber. The different infiltrations of the coating into nano-notches and its effect on the filament tensile properties were characterized, as well as discussing the impact of the VDP coating with an interlayer between the coating and the fiber.