Synthesis and Characterization of Poly(ether-block-amide) Membranes

Poly(ether-block-amide) membranes were made via casting a solution on a nonsolvent (water) surface. In this research, effects of different parameters such as ratio of solvent mixture (n-butanol/isopropanol), temperature, composition of coagulation bath (water) and polymer concentration, on quality of the thin film membranes were studied. The mechanism of membrane formation involves solution spreading, solvent–nonsolvent exchange, and partial evaporation of the solvent steps. Solvent- nonsolvent exchange is the main step in membrane formation and determines membrane morphology. However, at higher temperature of polymeric solution greater portion of solvent evaporates. The results showed that type of demixing process (mutual affinity between solvent and nonsolvent) has important role in film formation. Also, addition of solvent to the nonsolvent bath is effective on membrane morphology. The film quality enhances with increasing isopropanol ratio in the solvent mixture. This behavior can be related to increasing of solution surface tension, reduction of interfacial tension between solution and nonsolvent and delayed solvent-nonsolvent demixing. Uniform films were made at a temperature rang of 60–80 °C and a polymer concentration of 4–7 wt%. Morphology of the membranes was investigated with scanning electron micrograph (SEM). Pervaporation of ethyl butyrate/water mixtures was studied using these membranes and high separation performance was achieved. For ethyl butyrate/water mixtures, It was observed that both permeation flux and separation factor increase with increasing ethyl butyrate content in the feed. Increasing temperature in limited range studied resulted in decreasing separation factor and increasing permeation flux.     

Effect of poly(ethylene glycol) 200 on the formation of a polyetherimide asymmetric membrane and its performance in aqueous solvent mixture permeation

To investigate the effect of poly(ethylene glycol) (PEG) 200 on membrane performance, asymmetric polyetherimide (PEI) membranes with a small pore size were prepared by dry/wet-phase inversion from the casting solution containing N-methyl-2-pyrrolidone as a solvent and poly(ethylene glycol) 200 as an additive. Our experiment revealed that the addition of PEG 200 has an influence on the casting solution properties, permeation properties, and resulting membrane structures. Moreover, a drying process also affects the formation of a dense skin layer. Increasing the amount of PEG 200 drastically improved the solute rejection rate. The drying process improved the rejection rate. We also observed the effect of the mixed solvent (water/ethanol) on permeation through the membranes with various pore sizes. In the case of the membrane with a dense skin layer, the solvent permeation showed relationships with solution viscosity, surface tension, and membrane-solvent interaction.     

Characterization of the PPO dense membrane prepared at different temperatures by ESR,atomic force microscope and gas permeation

Dense (homogeneous) membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by using 1,1,2-trichloroethylene as a solvent at different solvent evaporation temperatures (22,4 and −10°C). The effect of temperature used during evaporation of solvent on the characteristics of the membrane was studied by using electron spin resonance, atomic force microscopy and gas permeation rate. The morphology of the surfaces of the membrane, the shape of spin probe in the membrane, and the selectivity of gases depend on the temperature of evaporation of solvent. The permeation rate of CO₂ increased with the decrease in the temperature used for the preparation of the membrane. However methane permeation rate increased in the membrane prepared at −10°C. It is suggested that Langmuir sites could be favorable for the CH₄ permeation.     

Effects of pressurized hot water extraction on the nanoscale structure of birch sawdust

Pressurized hot water extraction with a flow-through system was used to extract hemicelluloses and lignin from birch sawdust. The structure of the extraction residue was studied on various levels. Molecular mass distributions were determined with gel permeation chromatography and the crystal structure of cellulose was characterized using wide-angle X-ray scattering (WAXS). Information on the short-range order of cellulose microfibrils and on the nanoscale pore structure was obtained with small-angle X-ray scattering (SAXS), and the micrometre scale cellular morphology was imaged with X-ray microtomography. The pressurized hot water treatment was observed to increase the lateral width of cellulose crystallites, determined with WAXS, whereas a possible small decrease in the crystallinity of cellulose compared to native wood was detected. The molecular mass of cellulose remained at a relatively high level. According to the SAXS results, a tighter lateral association of cellulose microfibrils was observed in the extracted samples, which possibly led to opening of pores between bundles of microfibrils, as indicated by an increased specific surface area. A reduction in the thickness of the fibre cell walls was evidenced by X-ray microtomography.     

扑热息痛分子印迹聚合物膜选择性结合和渗透性质的研究

采用紫外光引发原位聚合的方法制备了具有支撑膜的扑热息痛分子印迹聚合物膜. 紫外分光光度法证明了模板分子与功能单体之间存在相互作用, 并据此选择了聚合反应时合适的溶剂. 用傅立叶红外光谱和扫描电镜分别测定了膜的结构和表面形貌. 渗透实验结果表明渗透时所用溶剂对渗透结果有重要影响. 合适的渗透溶剂可提高印迹膜对模板分子的渗透选择性.     

Physicochemical Characterization of Transport in Nanosized Membrane Structures

The understanding of polymer–solvent interactions is highly important for the development of tailored membrane manufacturing procedures and for the prediction of membrane performance from transport mechanisms. This study examines the permeation performance of organic solvents through state‐of‐the‐art polyimide membranes (STARMEM, Membrane Extraction Technology Ltd.). Solvents are systematically selected to allow investigation of the effects of key physicochemical transport parameters by keeping constant all other parameters thought to be relevant. The effect of the solubility parameter, polarity (dielectric constant), surface tension, and viscosity are studied in detail. Dead‐end permeation experiments are carried out at 20 bar with STARMEM 122 and STARMEM 240 membranes. Results for the selected solvents show higher permeation rates for ketones over alcohols and aromatics as well as for acids. It is suggested that the viscosity and polarity have a greater influence than the other parameters. The effect of solvent molar volume is also investigated. Transport of solvents with high molar volume, independent of their polarity and compatibility with the membrane material, is slower in all cases than for solvents with smaller molar volume. The solubility parameter does not show any significant effect on transport phenomena.     

Influence of drying method on morphology and properties of asymmetric cellulose hollow fiber membrane

Using a dry/wet spinning process, asymmetric cellulose hollow fiber membranes (CHFM) were prepared from a dope composed of cellulose/N-methylmorpholine-N-oxide/water. The formation mechanism for the finger-like macrovoids at the inner portion of as-spun fibers was explained. Naturally drying and three solvent exchange drying methods were tried to investigate their influence on morphology and properties of CHFM. It was found that the ethanol–hexane exchange drying was an appropriate method to minimize morphology change of the as-spun CHFM, whereas the naturally drying caused the greatest shrinkage of the fibers that made the porous membrane become dense. As a result, CHFM from ethanol–hexane exchange drying performed the highest gas permeation rate but gas permeation of the naturally dried membrane could not be detectable. The resultant CHFM from the ethanol–hexane exchange drying also showed acceptable mechanical properties, thus it was proposed to be an appropriate method for gas separation purpose. The experimental results supported the proposed drying mechanism of CHFM. The free water would evaporate or be replaced by a solvent that subsequently would evaporate but the bonded water would remain in the membrane. What dominated the changes of membrane morphology during drying should be the molecular affinities of cellulose–water, water–solvent and solvent–solvent.     

Gas and liquid permeation properties of modified interfacial composite reverse osmosis membranes

Gas permeation tests using nitrogen, oxygen, hydrogen, helium and carbon dioxide were performed to assess how membrane modification procedures affect the separating layer morphology of thin-film composite reverse osmosis membranes. Gas selectivity data provided evidence for the presence of nanoscale separating layer defects in dry samples of six commercial membrane types. These defects were eliminated when the membrane surface was coated with a polyether–polyamide block copolymer (PEBAX 1657), as indicated by a 25-fold decrease in gas permeance and at least a 2-fold increase in most selectivity values. Treatment with n-butanol followed by drying reduced water flux and gas flux by 30% and 75%, respectively, suggesting that using n-butanol as a solvent for applying coatings negatively affects membrane performance. The results of this study demonstrate that gas permeation measurements can be used to detect morphological features that impact gas and water membrane flux.     

Preparation and thermal treatment of Pd/Ag composite membrane on a porous α-alumina tube by sequential electroless plating technique for H2 separation

Pd/Ag/α-Al2O3 composite membranes were prepared by sequential electroless plating technique. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spec-troscopy, and inductively coupled plasma atomic emission spectroscopy techniques (ICP-AES). Effects of annealing time, Ag content, and air treatment on the hydrogen permeation flux and morphology of the alloys were investigated. The results of the investigation showed that the prepared type of tube had a good potential as substrate for membrane preparation. In addition, a uniform defect-free alloy was prepared by annealing at 550 ℃ in H2 atmosphere. The permeation results showed an increase in H2 permeation flux by increasing the Ag content and the annealing time. In addition, the air treatment of the prepared membranes at 400 ℃ for 1 h changed the morphology of the alloy and substantially enhanced the hydrogen flux.     

Preparation and characterization of PVDF microporous membrane with highly hydrophobic surface

Using the mixture of triethyl phosphate (TEP) and N,N‐dimethylacetamide (DMAc) as solvent, PVDF microporous membranes with highly hydrophobic surface were prepared by a modified NIPS method with a dual coagulation process. The effects of the exposure time on these membranes before being immersed into the coagulation bath and the composition in the coagulation bath on precipitation rate, membrane morphology, membrane hydrophobicity, membrane mechanical property, and membrane performance were studied. The morphologies and hydrophobicities of PVDF microporous membranes were investigated by scanning electron microscopy (SEM) and contact angle (CA) measurement. The precipitation processes were observed by light transmittance measurement. The pore size distribution was determined by liquid permeation technique. PVDF microporous membrane obtained by passing evaporation period of 60 min before being immersed into the water bath showed a high water CA of 122.1°. Using ethanol (EtOH) as coagulation bath, the water CAs of the top surface and bottom surface of the membrane increased to 125.9 and 132.6°, respectively. To further improve PVDF membrane hydrophobicity, a dual coagulation process was used and the mixed solvent (TEP–DMAc) was added into the first coagulation bath for 30 sec. Increase in the TEP–DMAc content led to the change in the morphology type of the membrane, that is, from an asymmetric structure with a dense top surface to a symmetric structure with a skinless top surface, and the pore size distribution widened greatly. By increasing the mass ratio of TEP to DMAc, the denseness of the membrane surface decreased significantly. Adding 60 wt% of TEP–DMAc to the first coagulation bath and the mass ratio of TEP to DMAc was 60:40, the CA reached to a maximum as high as 136.6°, and PVDF microporous membrane showed a high porosity of 80% and an excellent mechanical property of 3.14 MPa tensile strength and 61.79% elongation ratio. Copyright © 2009 John Wiley & Sons, Ltd.     

Dehydration of water-alcohol mixtures by pervaporation and vapor permeation through surface resintering expanded poly(tetrafluoroethylene) membranes

For the purpose of separating aqueous alcohol mixtures by the use of the pervaporation and vapor permeation techniques, a surface resintering expanded poly(tetrafluoroethylene) (e-PTFE), membrane was investigated. The surface properties of the modified e-PTFE membranes were characterized by atomic force microscopy, scanning electron microscopy, and contact angle meter. The X-ray diffraction measurements show that the crystallinity of the e-PTFE membrane decreases with increasing the surface resintering temperature. The surface roughness decreases with the surface resintering temperature increases. The membrane exhibited water selectivity during all process runs. The effects of feed composition, surface resintering temperature, and molar volume of the alcohols on pervaporation and vapor permeation were investigated. Compared with the e-PTFE membrane without surface modified, the e-PTFE membrane with surface resintering treatment effectively improve the separation factor for pervaporation of aqueous alcohol mixtures. The separation performances of e-PTFE membranes in vapor permeation are higher than that in pervaporation.     

Effect of aqueous and organic solutions on the performance of polyamide thin‐film‐composite nanofiltration membranes

Polyamide/polyacrylonitrile thin‐film‐composite (TFC) nanofiltration (NF) membranes for the separation of oleic acid dissolved in organic solvents (methanol and acetone) were interfacially prepared by the reaction of trimesoyl chloride in an organic phase with an aqueous phase containing piperazine and m‐phenylene diamine. The interfacial reaction was confirmed by an investigation of the attenuated total reflection infrared spectrum. The surface morphology of the polyamide TFC membranes was examined with scanning electron microscopy. The hydrophilic properties of the membrane surfaces were conjectured on the basis of the ζ potential and contact angle. The effects of the monomer concentrations of the monomer blends (aliphatic and aromatic diamines) and drying times on various aspects of membrane performance, such as the solvents (water, alcohols, ketones, and hexane), permeation rates, and organic solute [poly(ethylene glycol) 200 and oleic acid] rejection rates, were investigated. All the membranes showed good solvent resistance. The polar solvent flux for water and methanol was higher than that for a nonpolar solvent (hexane). The membranes gave good rejection rates of oleic acid dissolved in methanol and acetone. The NF membranes were compared with various commercial membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2151–2163, 2002     

Preparation of high density polyethylene/polyethylene-block-poly(ethylene glycol) copolymer blend porous membranes via thermally induced phase separation process and their properties

<正>High density polyethylene(HDPE)/polyethylene-block-poly(ethylene glycol)(PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation(TIPS) process using diphenyl ether(DPE) as diluent.The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry(DSC).By varying the content of PE-b-PEG,the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy(SEM) and wide angle X-ray diffraction(WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis,Fourier transform infrared spectroscopy-attenuated total reflection(FTIR-ATR) and X-ray photoelectron spectroscopy(XPS).Water contact angle,static protein adsorption and water flux experiments were used to evaluate the hydrophilicity,antifouling and water permeation properties of the membranes.It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes.In the investigated range of PE-b-PEG content,the PEG blocks could not aggregate into obviously separated domains in membrane matrix.More importantly,PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation,but also enrich at the membrane surface layer.Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity,protein absorption resistance and water permeation properties,which would be substantially beneficial to HDPE membranes for water treatment application.     

PREPARATION OF HIGH DENSITY POLYETHYLENE/POLYETHYLENE-ΒLOCK- POLY(ETHYLENE GLYCOL) COPOLYMER BLEND POROUS MEMBRANES VIA THERMALLY INDUCED PHASE SEPARATION PROCESS AND THEIR PROPERTIES

High density polyethylene (HDPE)/polyethylene-Wock-poly(ethylene glycol) (PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation (TIPS) process using diphenyl ether (DPE) as diluent. The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry (DSC). By varying the content of PE-b-PEG, the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis, Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Water contact angle, static protein adsorption and water flux experiments were used to evaluate the hydrophilicity, antifouling and water permeation properties of the membranes. It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes. In the investigated range of PE-b-PEG content, the PEG blocks could not aggregate into obviously separated domains in membrane matrix. More importantly, PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation, but also enrich at the membrane surface layer. Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity, protein absorption resistance and water permeation properties, which would be substantially beneficial to HDPE membranes for water treatment application.     

Thermodynamic modeling and investigation of the formation of electrospun collagen fibers

Electrospun type I collagen fibers are very promising materials for tissue scaffold applications, but are typically fabricated from toxic solvents. Recently, electrospinning of type I collagen fibers by using environmentally friendly phosphate buffer saline (PBS)/ethanol solution has been explored. PBS/ethanol solvent systems offer better cell compatibility, but the high surface tension and high boiling point of the solvent system make the collagen difficult to electrospin and can cause inferior fiber morphology. In this study, the influence of solvent surface tension on the morphology of electrospun collagen fibers has been experimentally investigated and analyzed from a thermodynamics perspective. The analytical results indicate that solvents with high surface tension drive the formation of beads along the smaller, thinner fibers. In addition, beads with relatively small angular eccentricity were thermodynamically favorable. The experimental results presented herein corroborate the theoretical analysis and conclusions drawn from this study. The surface tension of the solvent has significant influence on the bead formation, especially in an aqueous system. The environmental humidity for the electrospinning process and the collagen concentration were also investigated. These parameters may result in variations of the evaporation-solidification rates, which consequently impact the formation and morphologies of electrospun collagen fibers. According to the thermodynamic analysis, uniform electrospun collagen fibers without beads can be obtained by manipulating solvent surface tension during the electrospinning process.     

Preparation and thermal treatment of Pd/Ag composite membrane on a porous alumina tube by sequential electroless plating technique for H2 separation

Pd/Ag/α-Al2O3 composite membranes were prepared by sequential electroless plating technique. The prepared membranes were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy, and inductively coupled plasma atomic emission spectroscopy techniques （ICP-AES）. Effects of annealing time, Ag content, and air treatment on the hydrogen permeation flux and morphology of the alloys were investigated. The results of the investigation showed that the prepared type of tube had a good potential as substrate for membrane preparation. In addition, a uniform defect-free alloy was prepared by annealing at 550 ℃ in H2 atmosphere. The permeation results showed an increase in H2 permeation flux by increasing the Ag content and the annealing time. In addition, the air treatment of the prepared membranes at 400 ℃ for 1 h changed the morphology of the alloy and substantially enhanced the hydrogen flux.     

聚三甲硅基丙炔超薄复合膜的制备及氧氮透过性

聚三甲硅基丙炔超薄复合膜的制备及氧氮透过性邢晶＊张金兰郑国栋徐纪平（中国科学院长春应用化学研究所长春１３００２２）关键词聚三甲硅基丙炔，超薄复合膜，制备，氧氮透过性１９９６－１０－２３收稿，１９９７－０２－１７修回聚三甲硅基丙炔（ＰＴＭＳＰ）是目前透...     

Enantioselective permeation of racemic alcohol through polymeric membrane

Copolymer of 1,2-bis(2-methyl-1-triethylsiloxy-1-propenyloxy)ethane and dialdehyde have been synthesized by Mukaiyama Aldol polymerization using lipase as the catalyst. The chirality of the polymer was tested by optical rotation and circular dichroism study. The membrane forming ability of this chiral polymer was examined by casting the membrane in three different solvents viz., N-methyl-2-pyrilidone (NMP), dimethyl formamide (DMF) and dimethyl acetamide (DMAc) using the phase inversion method and it was found that chiral polymer–NMP membranes formed more uniform and regular surface morphology as was evident from SEM analysis. The enantioselective membranes prepared in the solvents was tested for resolution of racemic alcohol and it was found that NMP is the best solvent for obtaining highest enantioselectivity value. It was also found that the enantioselectivity for adsorption favoured the (S)-isomer whereas permeation favoured the (R)-isomer which is confirmed from interpretation of the adsorption isotherm by Langmuir model. Accordingly, the enantioselective permeation was caused by suppression of the (S)-isomer permeation. Optical resolution of (±)trans-sobrerol was achieved by pressure driven permeation through the membrane. The highest enantioselectivity, enantiomeric excess and permeation co-efficient was obtained as 98.59%, 20.42 and 13.627 m² h⁻¹, respectively. With an increase in polymer content in the membrane, the permeation rate increases.     

Factors affecting the nodule size of asymmetric PMMA membranes

Several factors that may affect the surface nodule size of a polymeric membrane were under investigation. The increase of polymer concentration and molecular weight were found to increase the surface nodule size. The increase of casting temperature also resulted in an increase in nodule size. These results supported that the radius of gyration and the collision frequency between polymer chains were the key factors affecting the nodule size. However, when the radius of gyration was reduced by the use of a poor solvent or by pre-adding nonsolvent in the casting solution, the surface nodule size increased. It suggested that there existed other factors affecting the nodule size on membrane surface besides the gyration radius and the collision frequency of polymer chains. In this study, we found in most cases that the surface nodule size decreased along with the surface tension difference between the casting solution and the coagulant. To demonstrate the effect of surface tension, we examined the nodule size inside the membranes where the nodule formation was not significantly affected by the interfacial tension. Opposite to what was observed on the surface, the nodule size increased with the solvation power of the solvent. This result suggested that it was the interfacial tension that overpowered the gyration radius in affecting the surface nodule size.     

The influence of the porous support layer of composite membranes on the separation of binary gas mixtures

Thin film composite (TFC) membranes exhibit a high flux for gas and vapor permeation and are viable for a wide range of applications. The high flux may also increase the importance of the resistance of the porous support structure depending on the application and process conditions. A comprehensive modeling approach for TFC membranes is introduced, which considers boundary layer resistances near the membrane surface, solution-diffusion through the coating, and the influence of the porous sublayer. Permeation through the support structure is described by the dusty gas model (DGM) with the support treated as a two-layered structure with a dense but porous skin and a more open substructure.The model accurately describes experimental data on TCE/nitrogen separation using a sweep gas on the permeate side very well. The main resistance towards TCE permeation through two different membranes tested is the porous support. It is shown that changes in the support morphology can greatly enhance the performance of the composite membranes. Model calculations were also performed for vacuum assisted permeation. The pressure drop across the support is considerable depending on the coating thickness. The TCE permeation is again dominated by the resistance of the support layer, which can be reduced by altering the morphological parameters of the structure.The proposed model is able to describe the performance of the composite membrane and to identify optimum process conditions for given performance characteristics. It can be used to aid in the development of membrane structures for enhanced performance.