Effects of THF as cosolvent in the preparation of polydimethylsiloxane/polyethersulfone membrane for gas separation

Polydimethylsiloxane/polyethersulfone (PDMS/PES) asymmetric membranes are widely applied in gas separation. However, the effects of common cosolvent on these membranes remain unknown. In order to study the changes in membrane morphology and gas separation properties, asymmetric PDMS/PES membranes were prepared. The studied parameters were types of cosolvents, tetrahydrofuran (THF) concentration, evaporation time, and PDMS concentration. Membrane morphology was examined using scanning electron microscopy and gas separation was conducted using pure CO₂, N₂, CH₄, and Hat 25°C. The addition of cosolvent into the polymer solution decreased the dope viscosity and delayed liquid–liquid demixing during phase inversion. Macrovoids formation was observed in substructure layer after adding THF and these macrovoids elongated with the reduction in THF content. There were microvoids formed on top of macrovoids and microvoids layer became thicker due to the increasing evaporation time of solvents before coagulation in nonsolvent. The PDMS coating on the PES membrane formed a dense skin layer and exhibited higher selectivity compared to the uncoated membrane. Membrane contained THF cosolvent with 60 s evaporation time and 3 wt% coated PDMS is the optimum membrane among other membranes in this work. The CO₂/N₂ selectivity was enhanced by 73.3% with CO₂ permeance of 44.86 GPU. POLYM. ENG. SCI., 54:2177–2186, 2014. © 2013 Society of Plastics Engineers     

Diffusion coefficient of DMF in acrylic fiber formation

A H₂O/dimethyl formamide (DMF) mixture was used as the coagulation bath of wet‐spun process for acrylic fibers. Diffusion coefficient of DMF in the protofibers prepared by acrylonitrile/acrylamide copolymers was determined. It has been found that diffusion coefficient of DMF outflow of the protofibers prepared by acrylonitrile/acrylamide copolymers synthesized by solution polymerization is highest compared with those of acrylonitrile/acrylamide copolymers synthesized by H₂O/DMF mixture suspension polymerization and aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMF decreases continuously. Diffusion coefficient of DMF increases along with the bath temperature, but the changes in diffusion coefficient values are less prominent as temperature goes beyond 55°C. When DMF concentration in the coagulation bath was 50%, the value of the diffusion coefficient of DMF was minimal. Diffusion coefficient of DMF increases along with jet stretch minus ratio increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3616–3619, 2006     

湿纺工艺纺制PAN中空纤维成形机理研究

利用C型喷丝板进行挤出凝固,采用湿法纺丝工艺制备聚丙烯腈(PAN)中空纤维,从PAN/二甲基亚砜(DMSO)纺丝原液的流变性能和凝固过程的相分离两个方面探讨了PAN中空纤维的成形机理。结果表明:纺丝液随剪切速率(γ)的增加逐渐发生由粘性向弹性的转变是挤出胀大的主要原因,其粘弹转变点随着温度的升高而向高γ移动,在60℃下的纺丝液弧片接触成孔的理论临界γ为212 s~(-1);纺丝液在凝固浴中表层成膜是PAN-DMSO-H_2O三元体系相分离的结果,纺丝液细流表面成膜速度是影响孔结构闭合的重要因素,可以通过凝固浴浓度和凝固浴调节剂来控制。     

Diffusion coefficient of DMSO in polyacrylonitrile fiber formation

A H₂O/dimethyl sulfoxide(DMSO) mixture was used as the coagulation bath for the wet‐spun process of acrylonitrile/ammonium itaconate copolymers fibers. Diffusion coefficient of DMSO in the protofibers prepared by acrylonitrile/ammonium itaconate copolymers was determined. It has been found that diffusion coefficient of DMSO outflow of the protofibers prepared by acrylonitrile/ammonium itaconate copolymers synthesized by the solution polymerization is highest compared with those of acrylonitrile/ammonium itaconate copolymers synthesized by H₂O/DMSO mixture suspension polymerization and the aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMSO decreases continuously. Diffusion coefficient of DMSO increases along with the bath temperature, but the changes of diffusion coefficient values are less prominent as temperature goes beyond 60°C. When DMSO concentration in the coagulation bath was 55 wt %, the value of the diffusion coefficient of DMSO was minimal. Diffusion coefficient of H₂O increases with the jet stretch minus ratio increasing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4447–4451, 2006     

Diffusion dynamics of ionic liquids during the coagulation of solution spinning for acrylic fibers

The coagulation dynamics of acrylic polymer (PAN) with 1‐butyl‐3‐methylimidazolium chloride [BMIM]Cl as solvent for PAN and H₂O as nonsolvent was investigated in detail. On the basis of Fick's second law of diffusion, a mass‐transfer model of [BMIM]Cl from concentrated PAN/[BMIM]Cl solution was established as verified with the experimental data. The established model has a good fit with the experimental data and the diffusion coefficient D of [BMIM]Cl was calculated according to the model. The diffusion coefficient D decreased a little when the concentration of solution increased. As increasing the coagulation bath concentration, the diffusion coefficient D initially increased and then decreased, reaching a maximum of 5 wt% in the coagulation bath. The diffusion coefficient D decreased with the coagulation bath temperature. From the diffusion coefficient and the structure of the coagulated filament, it can be concluded that the diffusion rate of [BMIM]Cl from PAN concentrate solutions is relatively slow, which is prospective to prepare uniform‐structure fibers. POLYM. ENG. SCI., 48:184–190, 2008. © 2007 Society of Plastics Engineers     

The influence of membrane formation parameters on structural morphology and performance of PES/PDMS composite membrane for gas separation

In this study, influence of membrane preparation parameters on structural morphology and performance of polyethersulfone/polydimethylsiloxane (PES/PDMS) composite membrane was investigated for gas separation. Asymmetric PES flat sheet membranes were composed by phase inversion method and used as supports. PES composite membranes were fabricated by coating silicone rubber as selective layer on the top surface of support. Effects of different concentrations of PES and PDMS, solvent type, and support thickness on membrane performance were investigated for separation of oxygen from nitrogen. The optimized superior membrane was further modified using polyvinylidenfluoride, methanol and ethanol as additives in PES solutions and/or in water coagulation bath to promote the membrane capability. The results showed that addition of ethanol and methanol in cast solution and coagulation bath can greatly affect the morphology and hence the performance of the prepared membranes. The permeance changes have the contrary trend with solubility parameter difference between solvent and nonsolvent mixture, for instance when this parameter difference was lowest, higher permeance was obtained. Support and coating polymer concentration can control the permeance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Pervaporation of Acetaldehyde Aqueous Solution through Zeolite 3A-Polyurethane (PU) Composite Membrane

3A-filled hydrophilic polyurethane (PU) membranes were prepared by incorporating zeolite 3A into PU for pervaporation separation of acetaldehyde and water mixtures (acetaldehyde concentration 2 wt%–20 wt%). The composite membranes were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The morphology and thermal stability of these membranes were also investigated. The effects of zeolite 3A on the sorption, diffusion, and pervaporation performance were evaluated. The swelling study showed that 3A-PU membrane had higher swelling degree in acetaldehyde aqueous solution than in pure water. And the swelling degree of the composite membrane in acetaldehyde solution increased with the 3A content. The permeation flux and water/acetaldehyde separation factor first increased and then decreased with increasing 3A content. The reason may be that a proper quantity of 3A will enlarge the free volume fraction of PU while excessive 3A lead to its poor dispersion. The highest permeation flux of the composite membrane could reach 223 g · m^?2 · h^?1 and the maximum water/acetaldehyde selectivity achieved 7.5. The calculation of sorption selectivity and diffusion selectivity showed that diffusion played a more important role in this process.     

Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 μm have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent. © 1994 John Wiley & Sons, Inc.     

Preparation of porous PVC membrane via a phase inversion method from PVC/DMAc/water/additives

Poly(vinyl chloride) membranes were prepared via a phase inversion method, using N,N‐dimethylacetamide (DMAc) as solvent, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and sucrose as three typical additives and water as the coagulation medium. The phase diagrams of the PVC/DMAc/additives/water quaternary systems were constructed using cloud‐point experimental data. With the addition of the different additives, the effect of dope solution temperature on the dope solution viscosity and the structure of membranes were investigated. It indicates that the viscosity of the PVC/DMAc dope solution with the additive increase compared with the dope solution without any additive and the addition of the additives into the dope solution alter the morphology and structure of the resultant membranes during the phase‐inversion process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of coagulation bath temperature and polyvinylpyrrolidone content on flat sheet asymmetric polyethersulfone membranes

In this study, effects of coagulation bath temperature (CBT) and polyvinylpyrrolidone (PVP K15) concentration as a pore former hydrophilic additive on morphology and performance of asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from a PES/ethanol/NMP system via phase inversion induced by immersion precipitation in a water coagulation bath. The morphology of prepared membranes was studied by scanning electron microscopy (SEM), contact angle measurements, and mechanical property measurements. Permeation performance of the prepared membranes was studied by separation experiments using pure water and bovine serum albumin (BSA) solution as feed. The obtained results indicate that addition of PVP in the casting solution enhances pure water permeation flux and BSA solution permeation flux while reducing protein rejection. Increasing CBT results in macrovoid formation in the membrane structure and increases the membrane permeability and decreases the protein rejection. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Formation of polyurethane membranes by immersion precipitation. II. Morphology formation

Polyurethane membranes were prepared by an immersion precipitation process. The effects of dope concentration, coagulation bath composition, and the chemical structure of the polyurethane on the morphology of the membranes were studied. The degree of contraction was measured by quenching freshly formed polyurethane membranes in liquid nitrogen. A mechanism for the formation of membrane morphology during immersion precipitation is proposed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2124–2132, 1999     

Hollow Fiber Ultrafiltration Membranes from Poly(Vinyl Chloride): Preparation,Morphologies, and Properties

Hollow fiber poly(vinyl chloride) membranes were prepared by using the dry/wet spinning method. Cross-section, internal, and external surfaces of the hollow fibers structure were studied by SEM. The pore size and pore size distribution of the hollow fibers were measured by a PMI capillary flow porometer. UF experiments of pure water and aqueous solution of PVP K-90 were carried out. The effect of the PVC concentration on the hollow fibers mechanical properties was also investigated. It was found that the PVC fibers cross-sectional structure was affected by the polymer concentration in the dope solution. In particular, reduction of macrovoids size was observed when increasing PVC concentration from 15 to 19 wt%. The pore size distribution of the PVC hollow fibers was controlled by adjusting the PVC concentration. Indeed, an increase of PVC concentration up to 19 wt% leads to fibers with sharp pore size distribution (the 99% of pores is about 0.15 µm).The pure water permeation flux decreased from 162 to 128 (l/m² · h · bar), while the solute separation performance increased from 82 to 97.5%, when increasing the PVC concentration. The elongation at break, the tensile strength, and the Young's modulus of the PVC hollow fibers were improved with PVC concentration in dope solution.     

Characterization of poly(vinylidene fluoride) flat sheet membranes prepared in various ratios of water/ethanol for separator of li‐ion batteries: Morphology and other properties

PVDF, poly(vinylidene fluoride), membranes were prepared and investigated by a scanning electron microscope, a universal testing machine, and capillary porometer for its potential use as a separator in lithium ion batteries. The membranes were prepared by phase inversion with different polymer types, concentrations of solution, amounts of additive, and nonsolvent ratios of water/ethanol. The morphology of membranes is affected by the ratio of both the coagulation bath (water/ethanol) and a low molecular weight additive (polymer/solvent/additive). The results showed that significant variations in the membrane were detected when adding an additive to the casting solution or ethanol to the coagulation bath. With an increased concentration of ethanol, the upper structure was found to be transformed into a sponge‐like arrangement. In the case of Solef®1015 of the same polymer concentration, despite the higher molecular weight of 1015, a relatively small sized nucleus is formed, resulting in a denser network and relatively uniform membrane structure being formed. Mechanical testing showed that the tensile strength of the PVDF membranes increased when added to a 25 wt % ethanol coagulation bath, whereas it is decreased when added to higher concentrations of ethanol in the bath or additives in the casting solution. In a bath condition of water/ethanol = 75/25 wt % (Bath no. 2), the value of tensile strength is 7.11 and 7.52 MPa, for Solef®6010 20 wt % and Solef®1015 17 wt %, respectively. The thickness of the prepared membrane is 21–34 μm and the porosity is up to 50%. The electrolyte absorption changes of the fabricated membranes at different conditions are measured from 151 to 223 ± 15%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study on Streptomycin Sulfate Recovery by Batch Foam Separation

The feasibility of foam separation as a technique was assessed for the recovery of streptomycin sulfate from the waste solution by using an anionic surfactant sodium dodecyl sulfate (SDS). The experimental parameters examined were SDS concentration, superficial gas velocity, initial pH, and liquid loading volume. The results showed that sodium dodecyl sulfate as the surfactant for foam separation had good foaming quality and could effectively concentrate streptomycin sulfate of the aqueous solution by technology of foam separation. The enrichment ratio and the recovery rate of streptomycin sulfate were 4.0 and 85%, respectively under the best operating conditions of sodium dodecyl sulfate concentration 0.4 g/L, superficial gas velocity 300 mL/min, liquid loading volume 300 mL and initial pH 6.0 when streptomycin sulfate concentration was 0.5 g/L.     

Improvement of H2/CH4 Separation Performance of PES Hollow Fiber Membranes by Addition of MWCNTs into Polymeric Matrix

Carboxylated multiwalled carbon nanotubes (MWCNTs) were added to polyethersulfone hollow fiber membranes to improve their H₂/CH₄ separation properties. The addition of MWCNTs up to 1 wt% increased macrovoids formation in cross-section, while in 2 wt% loading, decreased due to increase in dope viscosity. The best gas separation performance for the mixed-matrix hollow fiber membranes was achieved at 1 wt% MWCNTs loading with hydrogen permeance of 69 GPU and H₂/CH₄ selectivity of 44.1 at 5 bar(g). Tensile test results showed that incorporation of MWCNTs into the polymeric matrix affected the mechanical properties of the fabricated membranes.     

Morphology and performance of polysulfone hollow fiber membrane

Polysulfone hollow fiber membranes were prepared via the dry-wet spinning process from dope solutions comprised of polysulfone, n-methyl-2-pyrrolidone, polyvinyl-2-pyrrolidone, and dodecylbenzene sulfonic acid, sodium salt. Morphology and performance of the membranes were affected by the compositions of coagulant and dope solution. Pore size and the water flux of the membrane increased by the addition of dodecylbenzene sulfonic acid, sodium salt to water in the coagulation bath, due to the changes of physicochemical properties of the outer coagulant. Addition of dodecylbenzene sulfonic acid, sodium salt to the dope solution also increased the pore size. The absence of polyvinyl-2-pyrrolidone, the pore forming agent, in the dope solution resulted in a remarkable decrease of pore size of the membrane. The distance between the spinneret and coagulation bath affected the membrane structure and performance. The membranes prepared in this study were suitable for hemofiltration in terms of molecular weight cut-off characteristics. © 1993 John Wiley & Sons, Inc.     

Preparation and gas separation properties of asymmetric polysulfone membranes by a dual bath method

Defect-free skinned asymmetric gas separation membranes were prepared by a dual bath coagulation method that is a wet/wet phase inversion technique. The membranes were cast from a polysulfone/N,N-dimethylacetamide solution. In two sequent nonsolvent baths, the first bath using iso-propanol (IPA) leads to the formation of a dense skin top layer and the second bath using water makes the actual polymer precipitation. The top skin layer thickness was governed by changing the immersion time of the first IPA bath. We suggest that the growth rate of the skin layer is to be determined by a diffusion process.     

强疏水性PDMS/PVDF微孔膜的制备及其性能研究

利用非溶剂相转化法（NIPS）,通过在聚偏氟乙烯(PVDF)铸膜液中加入聚二甲基硅氧烷(PDMS),制备了PDMS/PVDF共混疏水微孔膜,并研究了凝胶浴组成（水/乙醇）对铸膜液凝胶动力学、膜形貌、疏水性及力学性能的影响。结果表明,随着凝胶浴中乙醇百分含量由零增加至100 %时,PDMS/PVDF共混膜的断面上指状孔基本消失,海绵状孔结构贯穿断面;当凝胶浴中乙醇含量为100 %时,PDMS与PVDF发生分相;膜表面疏水性能增加,水接触角达到139.68 °;弹性模量、拉伸强度、断裂伸长率分别由（48.06±4.20）、（2.82±0.15） MPa、（92.90±2.53） %下降至（15.70±2.83）、（0.72±0.13） MPa、（15.47±1.63） %。     

Effect of Raw Multi-Wall Carbon Nanotubes on Morphology and Separation Properties of Polyimide Membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO₂ and CH₄ showed that the addition of r-MWCNTs into the dope solution increased the CO₂/CH₄ separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO₂ in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO₂/CH₄ separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO₂/CH₄ separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r–MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs.