Preparation of poly(4‐methyl‐1‐pentene) asymmetric or microporous hollow‐fiber membranes by melt‐spun and cold‐stretch method

Poly(4‐methyl‐1‐pentene) (PMP) hollow fibers were prepared and fabricated into gas separation or microporous membranes by the melt‐spun and cold‐stretched method. PMP resin was melt‐extruded into hollow fibers with cold air as the cooling medium. The effects of take‐up speed and thermotreatment on the mechanical behavior and morphology of the fibers were investigated. Scanning electronic microscope (SEM) photos were used to reveal the geometric structure of the section and surface of the hollow fibers. It was found that the original fiber had an asymmetric structure. A “sandwich” mode was used to describe the formation of this special fine structure. And a series of PMP hollow‐fiber membranes were prepared by subsequent drawing, and it was found that there was a “skin–core” structure on the cross section of these hollow‐fiber membranes. Asymmetric or microporous PMP hollow‐fiber membranes could be obtained by controlling posttreatment conditions. The morphology of these membranes were characterized by SEM, and the gas (oxygen, nitrogen, and carbon dioxide) permeation properties of the membranes was measured. The results indicate that the annealing time of the original fiber and the stretching ratio were the key factors influencing the structure of the resulting membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2131–2141, 2006     

Activated carbon‐filled cellulose acetate hollow‐fiber membrane for cell immobilization and phenol degradation

The activated carbon‐filled cellulose acetate (CA) hollow‐fiber membranes were prepared by using phase‐inverse technique and subsequently characterized by scanning electronic microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), and tensile analysis. The SEM observation demonstrated that the activated carbon‐filled CA hollow‐fiber membranes possess four‐layer structure, which consists of an external skin dense layer, an external void layer, a central sponge layer, and an internal skin dense layer, whereas the pure CA hollow‐fiber membranes lack the macrovoid layer. As the measurement of AFM, the roughness of both internal and external surface of activated carbon‐filled fibers is much higher than that of pure CA fiber, respectively. Higher Young's modulus and storage modulus of filled membranes indicate that the activated carbon particles were homogeneously dispersed in the polymeric matrix. To investigate the feasibility of the newly developed hollow‐fiber membranes for cell immobilization cells and to evaluate the inhibitory effect of phenol on immobilized cells, Pseudomonas putida ATCC 17484 was chosen to be immobilized on both pure CA and activated carbon‐filled hollow‐fiber membranes. Batch experiments for phenol biodegradation were carried out for both free suspension and immobilized cells at the initial concentration of 1500 mg/L phenol. In the case of free suspension, neither cell growth nor phenol degradation occurred to any measurable extent up to 35 h. We found that both pure CA fiber and activated carbon‐filled fiber immobilization systems can completely degrade the phenol. However, the biodegradation rate of activated carbon‐filled fiber system was higher than that of pure CA fiber system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 695–707, 2000     

Hydrophilic modification of high‐strength polyvinylidene fluoride hollow fiber membrane

The polyvinylidene fluoride (PVDF)/polyvinyl alcohol (PVA) polymer solutions were coated on the outer surface of PVDF matrix hollow fiber membrane. On the principle of the homogeneous‐reinforced (HR) membrane technology, the reinforced PVDF/PVA (RFA) hollow fiber membranes prepared through the dry‐wet spinning method. The performance of the RFA membranes varies with the PVA concentration in the polymer solution and is characterized in terms of pure water flux (PWF), porosity, a mechanical strength test, and morphology observations by a scanning electron microscopy (SEM). The results of this study indicate that PVA can apparently improve the hydrophilicity of the PVDF hollow fiber membranes. The growing enrichment of the hydrophilic components PVA on the membrane surface is determined by X‐ray photoelectron spectroscopy. The RFA membranes have a favorable interfacial bonding between the coating layer (PVDF/PVA) and the matrix membrane (PVDF hollow fiber membrane), as shown by SEM. The elongation at break of the RFA membranes increases much more than that of the matrix membrane that is endowed with the better flexibility of the membrane performance. PWF decreases much more compared with that of the matrix membrane. The RFA membranes have a lower flux decline degree during the process of protein solution and ink solution filtration compared with that of the matrix membrane. POLYM. ENG. SCI., 54:276–287, 2014. © 2013 Society of Plastics Engineers     

Dynamic layer‐by‐layer self‐assembly of organic–inorganic composite hollow fiber membranes

Multilayer membranes constructed layer‐by‐layer (LbL) is finding increasing importance in many separation applications. The efficient construction of LbL multilayer on to hollow fiber substrates may offer many new opportunities for industrial applications. An organic–inorganic composite hollow fiber membrane has been developed using a dynamic LbL self‐assembly. This poly(acrylic acid)/poly(ethyleneimine) multilayer was dynamically assembled onto the inner surfaces of ceramic hollow fiber porous substrates pretreated by Dynasylan Ameo silane coupling agents. The hollow fibers were subsequently heat crosslinked to obtain stable permselective membranes. The formation of multilayers on the hollow fibers was characterized with a SEM, EDX, an electrokinetic analyzer and IR spectra. The effects of layer number, feed temperature and water content in the feed on the pervaporation performance have been investigated. To the best of our knowledge, this is the first report of LbL assembly of polymer building blocks onto ceramic hollow fiber porous substrates. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3176–3182, 2012     

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

Composite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N₂ adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO₂ permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO₂/N₂ and CO₂/CH₄ also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO₂ preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO₂ solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44999.     

Effects of the oxidation temperature on the structure and properties of polyacrylonitrile‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of the oxidation temperature of the PAN hollow fiber precursor on the microstructure, specific surface, pore size distribution, and adsorption properties of PAN‐based activated carbon hollow fiber (PAN‐ACHF) were studied. When PAN hollow fibers were oxidized at 270°C, because of drastic oxidation, chain scission occurred, and the number of pores within and on the surface of the resultant PAN‐ACHF increased, but the pores were just in the thinner region of the skin of PAN‐ACHF. The surface area of PAN‐ACHF reached a maximum when the oxidation temperature was 270°C. The adsorption ratios to creatinine were all higher than 90% at all oxidation temperatures, and the adsorption ratio to VB₁₂ reached a maximum (97%) at 230°C. The dominant pore sizes of the mesopores in PAN‐ACHF ranged from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 203–207, 2005     

Pervaporation of water/alcohol mixtures through chitosan/cellulose acetate composite hollow‐fiber membranes

For the purpose of separating aqueous alcohol by the use of pervaporation technique, a composite membrane of chitosan (CT) dip‐coated cellulose acetate (CA) hollow‐fiber membranes, CT‐d‐CA, was investigated. The effects of air‐gap distance in the spinning of CA hollow‐fiber membranes, chitosan concentration, and sorts of aqueous alcohol solutions on the pervaporation performances were studied. Compared with unmodified CA hollow‐fiber membrane, the CT‐d‐CA composite hollow‐fiber membrane effectively increases the permselectivity of water. The thickness of coating layer increases with an increase in chitosan concentration. As the concentration of chitosan solution increased, the permeation rate decreased and the concentration of water in the permeate increased. In addition, the effects of feed composition and feed solution temperature on the pervaporation performances were also investigated. The permeation rate and water content in permeate at 25°C for a 90 wt % aqueous isopropanol solution through the CT‐d‐CA composite hollow‐fiber membrane with a 5‐cm air‐gap distance spun, 2 wt % chitosan dip‐coated system were 169.5 g/m² h and 98.9 wt %, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1562–1568, 2004     

Development of thin‐film composite hollow‐fiber membranes from modified polyphenylene oxide for gas separation applications

The effect of sulfonation and bromination‐sulfonation on the gas transport properties of polyphenylene oxide has been investigated. These high‐performance modified polymers have been studied in the form of TFC membranes by solution coating on the skin side of polyetherimide hollow fibers. TFC membrane modules prepared from sulfonated‐brominated polyphenylene oxide as the active layer coated on polyetherimide hollow fibers. Stability of the TFC membranes was greatly improved when a wet feed stream was used instead of a dry one. Water vapor in the feed stream most likely prevented the active layer from stress cracking on drying. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 275–282, 2001     

Modified silicone–PVDF composite hollow‐fiber membrane preparation and its application in VOC separation

Polydimethylsiloxane^vi–poly(vinylidene fluoride) (PDMS^vi–PVDF) composite membranes were prepared using asymmetric PVDF hollow‐fiber membranes as the substrate where a very thin layer of silicone‐based coating material was deposited via a developed dip coating method. The preparation of the composite membranes under various conditions were investigated. In the optimal coating procedure, homogenous and stable oligo‐PDMS^vi coating layers as thin as 1–2 μm were successfully deposited on the surface of PVDF membranes. The developed PDMS^vi–PVDF composite membranes were applied for separation of a wide variety of volatile organic compounds (benzene, chloroform, acetone, ethyl acetate, and toluene). The results showed that the PDMS^vi–PVDF hollow‐fiber composite membranes that had been developed exhibited very high removal efficiency (>96%) for all the VOCs examined under favorable operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Poly(vinyl alcohol) coating on copper filament via electrospinning

Nanofiber‐coated conductive filaments, made by electrospinning, can be used extensively in various electronic applications, such as membranes for manufacturing fiber‐shaped batteries and supercapacitors. However, research on the fiber coating mechanism is necessary in order to be able to control the surface morphology and thickness of coated layers. In this study, fiber‐shape coated layers of poly(vinyl alcohol) were electrospun onto conductive filaments. The jet behaviors at various nozzle‐to‐collector distances were observed using charge‐coupled devices and high‐speed cameras. The mechanism of the coating process was determined from visible evidence and an appropriate coating model is suggested. Differences in jet behavior induce differences in the coating location on the filament surface. Consequently, the surface morphology and the thickness uniformity of the coated layer are changed. © 2017 Society of Chemical Industry     

Effect of precoated carbon layer on microstructure and anti‐erosion properties of SiC coating for 2D‐C/C composites

To improve the erosion resistant of carbon‐carbon composites, an SiC coating was synthesized on carbon‐carbon composites by the in situ reaction method. They are firstly coated with carbon layer by slurry, and then SiC coatings are obtained by chemical vapor reaction. The effects of precoated carbon layer on the microstructure and anti‐erosion properties of SiC‐coated C‐C composites were studied and characterized. The thickness of the SiC coating increased with the increase in the precoated carbon layer thickness. The different thickness of carbon layer affects hardness of the SiC coatings, resulting in diverse erosion resistance of the coatings. The SiC coating prepared with moderate thickness of precoated carbon layer exhibits the best erosion resistance, and show better resistance at an impact angle of 30° than 90°. The eroded surface revealed that coating cracking and brittle fracture, fiber‐matrix debonding, fiber breakage, and material removal, and the additional microcutting and microploughing at oblique impact angle are the major erosion mechanism of SiC coating for C/C composites.     

Preparation and membrane performance of poly(ethylene-co-vinyl alcohol) hollow fiber membrane via thermally induced phase separation

Poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes with ultrafiltration performance were prepared from EVOH/glycerol systems via thermally induced phase separation (TIPS). The diluent glycerol was used as bore liquid to make a lumen of the hollow fiber for the purpose of prevention of the diluent evaporation and the larger pores formation at the inner surface of the hollow fiber. The obtained hollow fiber membranes showed asymmetric structures with skin layer near the outer surface, the larger pores just below the skin layer and the smaller pores near the inner surface. The formation of the larger pores near the outer surface was due to the enhanced pore growth by the water penetration. Some primary factors affecting the structure and performance of the membranes such as ethylene content (EC) in EVOH, cooling water bath temperature and take-up speed were studied extensively. The water permeability can be improved by increasing the water bath temperature and the take-up speed and by decreasing the EC. Both the pore size at the outer surface and the connectivity between the pores have to be considered together to understand the experimental result of the water permeability and the solute rejection.     

Recognition properties of poly(vinylidene fluoride) hollow‐fiber membranes modified by levofloxacin‐imprinted polymers

Through the use of thermal polymerization, poly(vinylidene fluoride) (PVDF) hollow‐fiber membranes modified by a thin layer of molecularly imprinted polymers (MIPs) were developed for the selective separation of levofloxacin. To demonstrate the changes induced by thermal polymerization, PVDF hollow‐fiber membranes with different modification degrees by repeated polymerization were weighed. The total weight of the imprinted membranes increased by 14 μg/cm² after a five‐cycle polymerization. An increase in the membrane weight indicated the deposition of an MIP layer on the external surface of PVDF hollow‐fiber membranes during each polymerization cycle, which was also characterized by scanning electron microscopy. MIP membranes with different degrees of surface modification provided highly selective binding of levofloxacin. Both hollow‐fiber MIP membranes and nonimprinted membranes showed enhanced adsorption of levofloxacin and ofloxacin gradually with an increase in the modification degrees of PVDF hollow‐fiber membranes to a maximum value followed by a decrease. These results indicate that thermal polymerization indeed produces an MIP layer on the external surface of PVDF hollow‐fiber membranes and that it is feasible to control the permeability by repeated polymerization cycles. Different solvent systems in the permeation experiments were used to understand the hydrophobic interaction as one of the results of the binding specificity of MIP membranes. Selective separation was obtained by multisite binding to the template via ionic, hydrogen‐bond, and hydrophobic interactions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and Properties Study of Core‐Shell CL‐20/TATB Composites

The insensitive high explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) was selected for coating and desensitization of hexanitrohexaazaisowurtzitane (CL‐20), another high explosive, after surface modification. About 2 wt‐% polymer binder was adopted in the preparation process to further maintain the coating strength and fill the voids among energetic particles. The structure, sensitivity, polymorph properties, and thermal behavior of CL‐20/TATB by coating and physical mixing were studied. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) results indicate that submicrometer‐sized TATB was compactly coated onto the CL‐20 surface with coverage close to 100 %. The core‐shell structure of CL‐20/TATB was confirmed by observation of hollow TATB shell from the CL‐20 core dissolved sample. X‐ray diffraction (XRD) analysis revealed that the polymorph of CL‐20 maintained ε form during the whole preparing process. Thermal properties were studied by thermogravimetry (TG) and differential scanning calorimeter (DSC), showing effects of TATB coating on the polymorph thermal stability and exothermic decomposition of CL‐20. Both the impact and friction sensitivities were markedly reduced due to the cushioning and lubricating effects of TATB shell. The preparation of explosive composites with core‐shell structure provides an efficient route for the desensitization of high explosives, such as CL‐20 in this study.     

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes prepared from PVDF‐co‐HFP/PEG‐600Mw/DMAC solution for membrane distillation

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes were prepared by using the phase inversion method. The effect of polyethylene glycol (PEG‐600Mw) with different concentrations (i.e., 0, 5, 7, 10, 12, 15, 18, and 20 wt %) as a pore former on the preparation and characterization of PVDF‐co‐HFP hollow fibers was investigated. The hollow fiber membranes were characterized using scanning electron microscopy, atomic force microscopy, and porosity measurement. It was found that there is no significant effect of the PEG concentration on the dimensions of the hollow fibers, whereas the porosity of the hollow fibers increases with increase of PEG concentration. The cross‐sectional structure changed from a sponge‐like structure of the hollow fiber prepared from pure PVDF‐co‐HFP to a finger‐like structure with small sponge‐like layer in the middle of the cross section with increase of PEG concentration. A remarkable undescribed shape of the nodules with different sizes in the outer surfaces, which are denoted as “twisted rope nodules,” was observed. The mean surface roughness of the hollow fiber membranes decreased with an increase of PEG concentration in the polymer solution. The mean pore size of the hollow fibers gradually increased from 99.12 to 368.91 nm with increase of PEG concentration in polymer solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Positively charged hollow‐fiber composite nanofiltration membrane prepared by quaternization crosslinking

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by interfacial polymerization to develop a positively charged dense network structure. According to this mechanism, a positively charged hollow‐fiber composite nanofiltration (NF) membrane was prepared by quaternization to achieve a crosslinked PDMAEMA gel layer on the outer surface of polysulfone hollow‐fiber ultrafiltration (UF) membranes with a PDMAEMA aqueous solution as a coating solution and p‐xylylene dichloride as an agent. The preparation conditions, including the PDMAEMA concentration, content of additive in the coating solution, catalyzer, alkali, crosslinking temperature, and hollow‐fiber substrate membrane, were studied. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the structure of the membranes. This membrane had a rejection to inorganic salts in aqueous solution. The rejection of MgSO₄ (2 g/L aqueous solution at 0.7 MPa and 25°C) was above 98%, and the flux was about 19.5 L m^?2 h^?1. Moreover, the composite NF membranes showed good stability in the water‐phase filtration process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of braided tube reinforced polyacrylonitrile hollow fiber membranes

Polyacrylonitrile (PAN) and polyester (PET) braided hollow tube that used as a special reinforcement are braided from their filaments via two‐dimensional weaving techniques. PAN braided tube reinforced homogeneous PAN hollow fiber membranes and PET braided tube reinforced heterogeneous PAN hollow fiber membranes are prepared by concentric circles squeezed‐coated spinning method. As for PAN hollow fiber membrane, the effects of PAN concentration on the performance of the prepared hollow fiber membranes are investigated in terms of pure water flux, protein rejection, mechanical strength, and morphology observations by a scanning electron microscope (SEM). The interfacial bonding state of the braided tube reinforced PAN hollow fiber membranes is studied by constant speed stretching method. Results show that the breaking strength of two‐dimensional braided tube reinforced PAN hollow fiber membranes is higher than 80 MPa. The structure of separation surface is similar to the structure of an asymmetric membrane. With the increase of polymer concentration, the membrane flux decreases while the retention rate of BSA increase. The membrane porosity and maximum pore size have the same decreasing tendency as the increase of PAN concentration. The results also show that the interfacial bonding state of the PAN two‐dimensional braided tube reinforced homogeneous PAN hollow fiber membranes is better than that of the PET two‐dimensional braided tube reinforced heterogeneous PAN hollow fiber membranes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41795.     

Highly scalable ZIF‐based mixed‐matrix hollow fiber membranes for advanced hydrocarbon separations

ZIF‐8/6FDA‐DAM, a proven mixed‐matrix material that demonstrated remarkably enhanced C₃H₆/C₃H₈ selectivity in dense film geometry, was extended to scalable hollow fiber geometry in the current work. We successfully formed dual‐layer ZIF‐8/6FDA‐DAM mixed‐matrix hollow fiber membranes with ZIF‐8 nanoparticle loading up to 30 wt % using the conventional dry‐jet/wet‐quench fiber spinning technique. The mixed‐matrix hollow fibers showed significantly enhanced C₃H₆/C₃H₈ selectivity that was consistent with mixed‐matrix dense films. Critical variables controlling successful formation of mixed‐matrix hollow fiber membranes with desirable morphology and attractive transport properties were discussed. Furthermore, the effects of coating materials on selectivity recovery of partially defective fibers were investigated. To our best knowledge, this is the first article reporting successful formation of high‐loading mixed‐matrix hollow fiber membranes with significantly enhanced selectivity for separation of condensable olefin/paraffin mixtures. Therefore, it represents a major step in the research area of advanced mixed‐matrix membranes. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2625–2635, 2014     

Research of polylactide porous hollow nanofiber membrane with high selective absorption characteristics

A porous hollow fiber membrane using polylactide (PLA), a representative bio-derived polymer, was successfully fabricated. The use of high surface area fabrics can effectively absorb liquids, making it possible to impart selective absorbency to fabrics made of hydrophobic PLA. In this study, a porous PLA fabric was developed by applying the porosity of the fiber surface depending on the solvent, and the change was confirmed by morphological image analysis. To increase the total surface area effectively, hollow fibers were fabricated with coaxial electrospinning to maintain the pores of the surface while having a hollow space, and the changed oil absorption based on the fiber structure was measured. To enhance the selective absorption of the fabric to the oil, a coating process using nanoparticle was added. Dodecyltrichlorosilane-treated silica became superhydrophobic by attaching special functional groups to the surface of the particles. The treated silica was coated on the surface of the fabric to provide the functionality. To confirm the selective absorbency of the coated fabric, changes in oil and water absorption were analyzed, and the performance of the fabric was demonstrated. The fabricated PLA porous hollow fiber membranes are expected to replace existing products in the fields of tissue engineering, biofilters, and environment-friendly fabrics.     

Morphology,order, light transmittance,and water vapor permeability of aluminum‐coated polypropylene zeolite composite films

In this study, the polypropylene–zeolite composite films having 2–6 wt % natural zeolite were coated with a thin film of aluminum (Al) by magnetron sputtering, and the contribution of the Al coating on film properties was investigated. The samples were characterized by EDX, X‐ray diffraction, SEM, AFM, UV–visible spectroscopy, and water vapor permeation analyses. The surface of the films coated with a smooth Al film having 98–131 nm thickness. EDX revealed that Al percentage on the surface appeared to be as 8–10 wt % indicating contribution of polymer surface under Al film to analysis. XRD analysis showed that the grain size of Al at the surface was 22–29 nm. The surface roughness increased after Al‐coating process. The transmission of coated films was very low for both UV and visible regions of the light spectrum. Permeation analysis indicated that water vapor permeation was lower for Al‐coated material. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011