Pore morphology control and hydrophilicity of polyacrylonitrile ultrafiltration membranes

The effects of different solvents (dimethyl formamide: DMF and dimethylsulfoxide: DMSO) on the solubility of polyacrylonitrile (PAN) were investigated by the phase diagrams of H₂O/DMF/PAN and H₂O/DMSO/PAN ternary systems through cloud‐point titration method at low polymer concentration. The influences of polymer concentrations and temperatures on the morphologies of PAN ultrafiltration membranes were elucidated. The morphologies of fabricated UF membranes were characterized by scanning electron microscopy (SEM) and atomic force microscope (AFM), and the basic performance of ultrafiltration including pure water flux and rejection of BSA were explored. At 25°C, the pure water flux of ultrafiltration membranes at the lower PAN content (16 wt % PAN in 84 wt % DMSO) reached 213.8 L/m/bar and the rejection of BSA was 100%. Interestingly, the water flux of UF membranes dramatically decreased to 20.6 L/m/bar (20 wt %) and 2.9 L/m/bar (24 wt %) when increasing PAN concentrations in DMSO. On the other hand, the hydrophilicity of membranes can be enhanced by increasing coagulation temperatures and polymer concentrations which were characterized by static contact angle, fitting well with the variation tendency of roughness. Although there are many works concerning on the effects of phase inversion conditions on the performance of PAN UF membranes, to our best knowledge, there is seldom works focusing on investigating the membrane hydrophilicity trend by adjusting phase inversion conditions. To disclose the reason of the enhanced hydrophilicity, the water and glycol contact angles of various membranes were measured and the surface tensions were presented. The results illustrated that the enhanced hydrophilicity of PAN UF membranes fabricated at higher temperatures or higher polymer concentrations was due to the higher polarity on membrane surface. Since the vast majority of ultrafiltration membranes in labs and in industrial scale have been fabricated by immersion phase inversion method, this work can provide a guidance to obtain hydrophilic PAN UF membranes by adjusting the process of phase inversion. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41991.     

Preparation of PVDF/CaCO3 hybrid hollow fiber membranes for direct contact membrane distillation through TIPS method

Poly(vinylidene fluoride) (PVDF)–CaCO₃ hybrid hollow fiber membranes with a cellular structure and prominent permeability were fabricated via the thermally induced phase separation method for membrane distillation. CaCO₃ nanoparticles were introduced to the casting solution to improve the properties of the membranes. The effect of CaCO₃ dosage on the morphology was investigated. The prepared membranes were characterized by differential scanning calorimetry, SEM, and atomic force microscopy. The results showed that liquid–liquid phase separation preceded solid–liquid phase separation during the spinning process. Low dosages of CaCO₃ had a strong influence on the crystallization of PVDF molecules. The contact angle of the membrane increased with the addition of CaCO₃ nanoparticles. The maximum dead end pure water flux was as high as 1295.5 L/(m² h). The direct‐contact membrane distillation flux of the optimized PVDF/CaCO₃ hybrid membrane achieved 63.98 kg/(m² h) at the feed temperature of 90 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43372.     

A design of composite hollow fiber membranes with tunable performance and reinforced mechanical strength

A new design of hollow fiber membranes with high mechanical strength, great surface area per volume ratio and tunable filtration performance is presented. This newly developed hollow fiber membrane was produced by an intensified production process, in which the processes of thermally induced phase separation (TIPS), non‐solvent induced phase separation (NIPS), and interfacial polymerization (IP) were combined. PVDF (polyvinylidene difluoride) hollow fiber membranes (produced by TIPS) were used as support substrates. Afterwards, PES (polyethersulfone) (made by NIPS) and PA (polyamide) layers (manufactured by IP) were coated one by one. The pure water permeability, molecular weight cut off (MWCO), salt rejection, tensile stress together with surface and cross‐sectional morphology indicate that the properties of the hollow fiber membranes can be easily adjusted from microfiltration‐like to nanofiltration‐like membranes only by varying the presence of the IP step and the concentration in the PES layer in the production system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41247.     

Bipolar nanofiltration membranes based on plasma modified microfilters

Track‐etched membranes were used as support for deposition of plasma polymerized layers and formation of bipolar nanofiltration membranes. The 75 KHz plasma reactor was applied for that purpose. Three kinds of monomers were plasma polymerized. They were as follows: n‐butylamine, allylamine, and acrylic acid. For each monomer, the best polymerization parameters were selected. It was determined that acrylic acid deposited at the highest rate, then deposited allyloamine and finally n‐butylamine. Among the electrodes, the grounded one offered more stable layer and can be used for plasma polymer deposition. The obtained membranes showed good rejection properties toward bivalent ions. It was shown that the sequence of deposited layers did not affect the separation properties. For some investigated membranes, rejection reached 50–80% value. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39790.     

Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared using the solvent spinning method. N,N-dimethylacetamide was the solvent and ethylene glycol was employed as non-solvent additive. The effect of the concentration of ethylene glycol in the PVDF spinning solution as well as the effect of ethanol either in the internal or the external coagulant on the morphology of the hollow fibers was investigated. The prepared membranes were characterized in terms of the liquid entry pressure of water measurements, the gas permeation tests, the scanning electron microscopy, the atomic force microscopy, and the solute transport experiments. Ultrafiltration experiments were conducted using polyethylene glycol and polyethylene oxides of different molecular weights cut-off as solutes. A comparative analysis was made between the membrane characteristic parameters obtained from the different characterization techniques.     

Preparation and characterization of a composite nanofiltration membrane from cyclen and trimesoyl chloride prepared by interfacial polymerization

A novel nanofiltration (NF) membrane was prepared with cyclen and trimesoyl chloride by interfacial polymerization on a poly(ether sulfone) ultrafiltration membrane with a molecular weight cutoff of 50,000 Da. The effects of the reaction time, monomer concentration, and heat‐treatment temperature are discussed. The physicochemical properties and morphology of the prepared NF membrane were characterized by Fourier transform infrared spectroscopy–attenuated total reflectance, scanning electron microscopy, energy‐dispersive spectrometry, and atomic force microscopy. The NF performances were evaluated with solutions of Na₂SO₄, MgSO₄, Mg(NO₃)₂, and NaCl. The salt‐rejection order of the prepared NF membrane was as follows: Na₂SO₄ > MgSO₄ > Mg(NO₃)₂ > NaCl. The resulting rejection of Na₂SO₄ and PEG600 (polyethylene glycol with the average molecular weight of 600) were more than 90%, whereas that of NaCl was approximately 10%. After the addition of silica sol in the aqueous phase (silica sol concentration = 0.1% w/v), the salt rejection of the membrane changed slightly. However, the water flux was from 24.2 L·m^?2·h^?1 (25°C, 0.6 MPa) up to 38.9 L·m^?2·h^?1 (25°C, 0.6 MPa), and the resulting membrane exhibited excellent hydrophilicity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42345.     

Preparation and characterization of carboxylated multiwalled carbon nanotube/polyamide composite nanofiltration membranes with improved performance

Polyamide thin‐film composite nanofiltration (NF) membranes were prepared via the interfacial polymerization (IP) process of piperazine and 1,3,5‐trimesoyl chloride on the polysulfone/nonwoven fabric ultrafiltration membrane surface. Carboxylated multiwalled carbon nanotubes (cMWNTs) were incorporated into the aqueous phase during the IP process to improve the membrane performance. The composition and morphology of the membrane surface were examined by means of attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy–energy dispersive spectrometry, and atomic force microscopy. The effects of the cMWNTs content on the membrane hydrophilicity, separation performance, and antifouling properties were characterized through water contact angle and crossflow filtration measurements. The experimental results show that membrane surface hydrophilicity, water permeability, salt rejection (R ), and antifouling properties all improved. In particular, when the cMWNTs content was 50 ppm, the magnesium sulfate R of the composite NF membrane reached a maximum value of 98.5%; meanwhile, the membrane obtained an obviously enhanced water flux (62.1 L m^?2 h^?1 at 0.7 MPa), which was two times larger than that of the original NF membrane. The modified NF membranes showed enhanced antifouling properties; this was mainly attributed to changes in the microstructures and surface features of the polyamide layer after the addition of the cMWNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45268.     

Codeposition of catechol–polyethyleneimine followed by interfacial polymerization for nanofiltration membranes with enhanced stability

Thin‐film composite (TFC) nanofiltration (NF) membranes were fabricated via the codeposition of catechol (CCh) and polyethyleneimine (PEI) followed by subsequent interfacial polymerization with trimesoyl chloride (TMC) on the surface of polysulfone ultrafiltration substrates. The detailed structures and surface properties were characterized by X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, ζ potential analysis, and water contact angle measurement. The surface properties, including the roughness, hydrophilicity, surface potential, and NF performances, were facilely tuned through variation of the codeposition time of CCh–PEI for the prepared TFC membranes. The optimized membrane achieved a high rejection (ca. 93%) of MgCl₂ with a flux of around 31 L m^?2 h^?1 under 0.7 MPa. The results also reveal that the codeposition process endowed the final membranes with much better structural stability in alcohol and improved chlorine resistance compared to commonly interfacial polymerized ones with PEI and TMC. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45422.     

Influence of surface properties on the dip coating behavior of hollow fiber membranes

Coating processes have become an important fabrication step in membrane production, either to form a separation layer on a porous substrate or to tune specific properties. The coating procedure depends to a large extent on the membrane properties which substantially impedes a prediction of the coating thickness. To give an insight into the coating properties of various hollow fiber membranes, a selection of membranes with different pore sizes was coated with aqueous poly(vinyl alcohol) solutions at various coating velocities. It was found that material properties and pore sizes of the membranes have great influence on coating thicknesses. An intrusion of coating material into the membrane structure was determined with increasing pore size. Pure intrusion without formation of a dense surface layer took place when using a membrane with a mean pore size of ca. 500 nm. Coating results were correlated with the theoretical LLD law and for some membranes the coating thickness can be predicted quite well by the LLD law and its enhancements. When a significant amount of coating material penetrated into the membrane structure the LLD law loses its validity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46163.     

Experimental study of the effect of zeolite 4A treated with magnesium hydroxide on the characteristics and gas‐permeation properties of polysulfone‐based mixed‐matrix membranes

Nowadays, new methods for gas‐separation processes are being quickly developed. The separation of CH₄/CO₂ and CH₄/H₂ is usually the subject of most related research studies, especially in the membrane gas‐separation process, because of their important role in industry. In this study, we attempted to improve the separation properties of a polysulfone/zeolite 4A mixed‐matrix membrane by modifying the zeolite particle surface. The method included a simple ion‐exchange reaction of magnesium chloride with ammonium hydroxide that yielded the formation and precipitation of magnesium hydroxide whiskers on the surface of the zeolites. The whiskers could omit most of the nonselective voids by interlocking the polymer chains through them and, consequently, improve the permeability, selectivity, and elastic modulus of the membranes. X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and dynamic mechanical analysis proved all the changes recorded after the particle and membrane treatments. SEM images showed the petal‐like morphology of the whiskers that formed on the surface of the particles after the reaction against the smooth surface of the untreated zeolite. At a 30 wt % loading of particles in the polymeric matrix, the selectivities for H₂/CH₄ and CO₂/CH₄ increased by 69 and 56%, respectively; in contrast, the H₂ and CO₂ permeabilities decreased by 2.5 and 10%, respectively. The modulus of elasticity for the treated membrane also increased by 14 and 30% compared to those of the pure and untreated membranes, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44329.     

Microstructure–performance relationships of hollow-fiber membranes with highly efficient separation of oil-in-water emulsions

The critical breakthrough pressure related to the membrane surface wettability and pore size is a key parameter determining membrane performance in particular applications, such as oil–water mixture separations. A series of hydrophilic polysulfone hollow-fiber membranes with different pore sizes were prepared and characterized to evaluate the separation performance of oil-in-water emulsions and to develop an optimum membrane for such emulsions. For the optimum membrane, the absolute value for the cosine of the surface oil droplet contact angle (0.72) was close to the ratio of the outer surface pore size to the oil droplet size (0.71); it was also similar to the absolute value of the cosine of the underwater oil contact angle on the polysulfone material (0.65). From the point of view of the surface wettability, theoretical calculations were performed to select a suitable membrane with the aim of reaching the maximum efficiency in practical oil–water mixture separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47615.     

Development of antifouling poly(vinyl chloride) blend membranes by atom transfer radical polymerization

In this study, antifouling poly(vinyl chloride) (PVC) blend membranes were prepared by blending the PVC based amphiphilic copolymer PVC‐g‐poly(hydroxyethyl methacrylate) (PVC‐g‐PHEMA), synthesized by atom transfer radical polymerization (ATRP), into the hydrophobic PVC matrix via the nonsolvent‐induced phase separation method. The in situ ATRP reaction solutions were also used as the blend additives to improve membrane performance. Attenuated total reflectance–Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy indicated that the blend membranes based on the two blend routes exhibited similar surface chemical compositions. The membrane morphology and surface wettability were determined by scanning electronic microscopy and water contact angle measurement, respectively. The blend membranes showed improved water permeability, comparable rejections and enhanced antifouling properties compared with the pure PVC membrane. The PVC blend membranes also had excellent long‐term stability in terms of chemical compositions and fouling resistance. The results demonstrated that ATRP was a promising technique to synthesize amphiphilic copolymer and prepare stable blend antifouling membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45832.     

Cellulose acetate and sulfonated polysulfone blend ultrafiltration membranes. I. Preparation and characterization

Modification of polymeric membrane materials by incorporation of hydrophilicity results in membranes with low fouling behavior and high flux. Hence, Polysulfone was functionalized by sulfonation and ultrafiltration membranes were prepared based on sulfonated polysulfone and cellulose acetate in various blend compositions. Polyethyleneglycol 600 was employed as a nonsolvent additive in various concentrations to the casting solution to improve the ultrafiltration performance of the resulting membranes. The total polymer concentration, cellulose acetate, and sulfonated polysulfone polymer blend composition, additive concentration, and its compatibility with polymer blends were optimized. The membranes prepared were characterized in terms of compaction, pure water flux, membrane resistance, and water content. The compaction takes place within 3–4 h for all the membranes. The pure water flux is determined largely by the composition of sulfonated polysulfone and concentration of additive. Membrane resistance is inversely proportional to pure water flux, and water content is proportional to pure water flux for all the membranes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1749–1761, 2002     

Nanomechanical mapping of glass fiber reinforced polymer composites using atomic force acoustic microscopy

In this work, a dual‐frequency resonance tracking (DFRT) method was applied on atomic force acoustic microscopy (AFAM) and high‐resolution, quantitative nanomechanical mapping of a glass fiber–reinforced polymer composites (GFRP) was realized. Results show that even using the single‐frequency AFAM, the fiber, and epoxy can give very good contrast in amplitude images. The modulus mapping result on GFRP by DFRT AFAM was compared with that by dynamic nanoindentation, and it is found that DFRT AFAM can map the elastic modulus with high spatial resolution and more reliable results. The interface of GFRP was especially investigated using a 2 μm × 2 μm scanning area. Finite element analysis was implemented to investigate the effect of tip radius and the applied pressing force on the interface measurement using a sharp “interface”. By setting a linear‐modulus‐varied interface with finite width in finite element analysis (FEA), similar comparison between FEA and AFAM experimental results was also implemented. The average interface width is determined to be 476 nm based on the high‐resolution modulus image, indicating that AFAM is a powerful method for nanoscale interface characterization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39800.     

CuO‐filled aminomethylated polysulfone hybrid membranes for deep desulfurization

CuO‐filled aminomethylated polysulfone hybrid membranes were prepared for sulfur removal from gasoline. The as‐prepared membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The separation performance of the hybrid membranes was evaluated by pervaporation (PV) separation of n‐heptane/thiophene binary mixture. CuO‐filling leads to a decrease in permeation flux. The sulfur‐enrichment factor increased first and then decreased with increasing CuO loading, and it is worth noting that there is a rebound in enrichment factor above 8 wt % CuO loading. Influencing factors such as nitrogen content, feed temperature, sulfur content, and various hydrocarbons on membrane PV performance were also evaluated. Permeation flux of 23.9 kg·μm·m^?2·h^?1 and sulfur‐enrichment factor of 3.9 can be achieved at 4 wt % CuO loading in PV of n‐heptane/thiophene binary mixture with 1500 μg·g^?1 sulfur content. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3718–3725, 2013     

Preparation and characterization of the modulus intermediate layer in carbon fiber/epoxy composites by depositing sepiolites

An important aspect in development of multi‐scale reinforced composites is their mass production which can be easily realized. In this article, the sepiolites (Si12O30Mg8(OH)4(OH2)4·8H2O) are directly deposited onto the surface of JH‐T800 carbon fibers for the first time with no need for removal of the commercial sizing agent. The sepiolites adhering to the carbon fibers are uniformly distributed with random orientation, and participated in the formation of high modulus intermediate layer encompassing the carbon fiber. After the deposition of sepiolites, the interfacial shear strengths (IFSS) of the carbon fiber/epoxy composites are significantly improved as shown in single‐fiber composite fragmentation tests. Compared to the commercial carbon fiber composites, the sepiolite‐deposited fiber composites also exhibit obvious improvement in the interlaminar shear strength and flexural strength. As a new kind of multi‐scale reinforcement with industrial application value, the sepiolite‐deposited carbon fibers can further raise the level of mechanical properties of the existing carbon fiber reinforced composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43955.     

Preparation and characterization of hydrophilic and antifouling poly(ether sulfone) ultrafiltration membranes modified with Zn–Al layered double hydroxides

Zn–Al layered double hydroxide (LDH)‐entrapped poly(ether sulfone) (PES) ultrafiltration membranes with four different weight percentages, 0.5, 1.0, 2.0, and 3.0%, were prepared by a phase‐inversion method. Characterization by scanning electron microscopy, atomic force microscopy and contact angle (CA), equilibrium water content, porosity, average pore size, mechanical strength, and ζ potential measurement were used to evaluate the morphological structure and physical and chemical properties of membranes. Static protein adsorption, filtration, and rejection experiments were conducted to study the antifouling properties, water permeability, and removal ability of the modified membranes. The results show that significant change occurred in the membrane morphology and that better hydrophilicity, water permeability, and antifouling ability were also achieved for the PES/LDH membranes when a proper amount of LDH was used. For example, the CA value decreased from 66.60 to 50.21°, and the pure water flux increased from 80.21 to 119.10 L m^?2 h^?1 bar^?1 when the LDH loading was increased from 0 to 2.0 wt %. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43988.     

Asymmetric polysulfone gas separation membranes treated by low pressure DC glow discharge plasmas

Asymmetric polysulfone (PSF) gas separation membranes were prepared at different conditions such as non‐solvent concentration, evaporation time (ET) and coagulation bath temperature (CBT). In addition, effects of low‐pressure DC glow discharge plasma on the characteristics of PSF membranes were investigated. PSF membranes both before and after plasma treatment were characterized by several techniques, including contact angle measurement, scanning electron microscope (SEM), dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM). Furthermore, the performance of membranes was evaluated in terms of permeability of CO₂, CH₄, O_2, and N₂ gases. The ideal selectivity of CO₂/CH₄ and O₂/N₂ and surface free energy was calculated. Results showed that the EtOH concentration, ET and CBT affect the morphology of PSF membranes. For membranes prepared from a casting solution consisting of PSF 26.0, NMP 28.0, THF 28.0, and EtOH 18.0 wt % and ET for 3 min, the maximum selectivity of untreated membrane is about 69.76 and 12.59 for CO₂/CH₄ and O₂/N₂, respectively. After plasma treatment, the ideal selectivity is receded; however, the CO₂/CH₄ is still higher than 40.41 at pressure of 5 bars. Finally, preparation conditions and DC glow discharge plasmas have significant effects on the characteristics of the PSF membranes and result in an increase of the gas permeation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42116.     

Surface modification of hollow glass microsphere with different coupling agents for potential applications in phenolic syntactic foams

Modified hollow glass microsphere (HGM) particles have been prepared by surface treatment. Coupling agents such as γ‐aminopropyltriethoxysilane (APTES), di(dioctylpyrophosphato) ethylene titanate (NDZ‐311), and glutaraldehyde (GA) were used as modifiers to improve the hydrophobicity of HGM. Compared with pristine HGM, the modified HGM, especially the particles coupled with APTES‐GA, show better properties on flexural strength, fracture toughness, and dynamic mechanical properties of phenolic syntactic foams. It is revealed that the coupling agent coating layer grafted onto the surface of HGM reduces the polarity of particles, avoiding agglomeration of HGM in phenolic matrix and exhibiting good interfacial interaction between HGM and phenolic matrix. The remarkable improvement of interfacial adhesion between APTES‐GA modified HGM and phenolic matrix is mainly due to the covalent linkage with phenolic resin while the physical entanglement of molecular chains dominates the linkage between other modified HGM and phenolic matrix. APTES‐GA treatment is a more appropriate surface modification method for inorganic particle reinforced phenolic matrix composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44415.     

Preparation,characterization, and performance evaluation of coated PES polymer materials fabricated via dry/wet phase inversion technique

Sulfur dioxide (SO₂) is the major air pollutant which is emitted from the power plant. In this study, hollow fiber membrane (HFM) separation process is applied for the improvement of SO₂ removal efficiency in the post‐combustion gas. HFM was produced by dry/wet phase inversion method and then coated with Polydimethylsiloxane (PDMS). The membrane morphology and characterization were examined with help of scanning electron microscope (SEM), energy dispersion of X‐ray spectroscopy (EDX), Fourier transform infrared (FT‐IR) and atomic force microscopy (AFM). Polyethersulfone (PES) hollow fiber membranes were tested for the SO₂/N₂ binary mixed gas separation. Single gas permeance of SO₂, N₂, and binary mixture gas (200 ppm of SO₂) separation experiment was initiated to observe membrane behavior according to temperature and pressure difference and retentate flow rate. As a result, permeance of SO₂ was 24.9–47.4 GPU and selectivity of SO₂/N₂ was 1.6–4.2. From the mixture gas separation experiment, SO₂ removal efficiency increased according to stage cut and operating pressure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39711.