Poly(vinyl chloride) hollow‐fiber membranes for ultrafiltration applications: Effects of the internal coagulant composition

Poly(vinyl chloride) (PVC) hollow‐fiber membranes were spun by a dry/wet phase‐inversion technique from dopes containing 15 wt % PVC to achieve membranes with different pore sizes for ultrafiltration (UF) applications. The effects of the N,N‐dimethylacetamide (DMAc) concentration in the internal coagulant on the structural morphology, separation performance, and mechanical properties of the produced PVC hollow fibers were investigated. The PVC membranes were characterized by scanning electron microscopy, average pore size, pore size distribution, void volume fraction measurements, and solubility parameter difference. Moreover, the UF experiments were conducted with pure water and aqueous solutions of poly(vinyl pyrrolidone) as feeds. The mechanical properties of the PVC hollow‐fiber membranes were discussed in terms of the tensile strength and Young's modulus. It was found that the PVC membrane morphology changed from thin, fingerlike macrovoids at the inner edge to fully spongelike structure with DMAc concentration in the internal coagulant. The effective pores showed a wide distribution, between 0.2 and 1.1 μm, for the membranes prepared with H₂O as the internal coagulant and a narrow distribution, between 0.114 and 0.135 μm, with 50 wt % DMAc. The results illustrate that the difference in the membrane performances was dependent on the DMAc concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt electrospinning from poly(L‐lactide) rods coated with poly(ethylene‐co‐vinyl alcohol)

Rodlike poly(L ‐lactide) (PLLA) samples coated with poly(ethylene‐co‐vinyl alcohol) (EVOH) were made. Fibers were produced from these rodlike samples by using a melt electrospinning system equipped with a laser irradiating device, and the effects of EVOH content and the processing parameters of the melt electrospinning on fiber diameters were investigated. We also studied the fiber formation mechanism from the rods during the laser melt electrospinning process. The following conclusions were reached: (i) coating of EVOH on PLLA rods has a remarkable effect on decreasing fiber diameter from 3 μm to around 1 μm; (ii) increases in the electric field strength and temperature of spinning space decrease the average diameter of fibers produced from pure PLLA rods, and longer collector distance leads to lager PLLA fiber diameter; and (iii) the migration of PLLA component from the core to the surface of electrospun fibers takes place during the fiber formation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Ion transport properties of porous polybenzimidazole membranes for vanadium redox flow batteries obtained via supercritical drying of swollen polymer films

A novel method of membrane preparation for use in vanadium redox flow batteries by preswelling of poly(2,5‐benzimidazole) films in organic solvent followed by supercritical CO₂ assisted solvent removal is proposed. Influence of the organic solvent type on the morphology, proton, and vanadyl ion transport properties is studied. The performance of the obtained membranes inside single cells of vanadium redox flow batteries is compared to pristine dense poly(2,5‐benzimidazole) and Nafion 115 membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46262.     

Stereocomplex formation between enantiomeric poly(lactic acid). VIII. Complex fibers spun from mixed solution of poly(D-lactic acid) and poly(L-lactic acid)

To obtain poly(lactic acid) (PLA) complex fibers, spinning was performed by wet and dry methods from 5–10 g/dL chloroform solutions of poly(D-lactic acid) (PDLA) and poly(L-lactic), both with a viscosity-average molecular weight of 3 × 10⁵. The dope was extruded from a monohole nozzle into coagulation baths from ethanol and chloroform for wet spinning and into a drying column kept at 60°C for dry spinning. Scanning electron microscopic observation of the as-spun fibers showed that the surface of the wet-spun fiber had large basins with diameters of 50–100 μm and many pores with diameters from sub μm to 10 μm, whereas the surface of dry-spun fiber had a microporous structure with the pore diameter of 1–3 μm. The tensile strength of the wet-spun complex fiber was very low and could not be drawn at high temperatures, in contrast to the dry-spun fiber. The tensile strength of dry-spun complex fiber increased upon hot drawing and showed the tensile strength of 94 kg/mm² by drawing at 160°C to the draw ratio of 13. Differential scanning calorimetry revealed that the complex fibers contained both the stereocomplex crystallites (racemic crystallites) and the crystallites of the single polymers, PDLA and PLLA, regardless of the spinning methods. The ratio of the racemic crystallites to the single-polymer crystallites increased with the draw ratio of the complex fiber. © 1994 John Wiley & Sons, Inc.     

Structure and performance of temperature‐sensitive poly(vinylidene fluoride) hollow fiber membrane fabricated at different take‐up speeds

Graft copolymer (PVDF‐g‐PNIPAAm) having poly(vinylidene fluoride) (PVDF) backbones and poly(N‐isopropylacrylamide) (PNIPAAm) side chains was synthesized via radical copolymerization and its hollow fiber membrane was fabricated from dry–wet spinning technique with N, N‐dimethylformamide as the solvent and poly(ethylene glycol) (10,000) as the additive. The effects of spinning condition (take‐up speeds) on the structures and performances of resulting fiber membranes were systematically considered. The structures and performances of fiber membranes were characterized by element analysis, X‐ray photoelectron spectroscopy, water contact angle measurement, scanning electron microscope, atom force microscope, and filtration experiments. The results indicate that PNIPAAm side chains tended to enrich on the membrane surface and pore surface and especially tended to aggregate on the inner surface due to the effect of bore fluid. The hollow fiber membrane exhibits an obvious temperature‐sensitive property. The pure water flux increases remarkably around 32°C, while the retention of albumin egg decreases accordingly, when the permeation temperature rises from 20 to 45°C. As the take‐up speed increases, both the inner and outer diameters of fiber membranes decrease. A higher take‐up speed favors higher pure water permeation flux, which allows larger molecules to permeate through the fiber membrane. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Polymeric piezoelectric fiber with metal core produced by electrowetting‐aided dry spinning method

An electrowetting‐aided dry spinning method is developed to produce morphologically stable polymeric piezoelectric fibers with a metal core covered by a beta‐phase poly(vinylidene fluoride) [or poly(vinylidene‐trifluoroethylene)] layer. Each fiber consists of a 100 μm copper core (enameled with 6 μm polyester‐imide), a 3–10 μm piezoelectric layer, and a sputtered 100 nm gold electrode. The morphological properties of the fibers are analyzed with scanning electron microscopy, X‐ray diffraction, and a step profiler. The piezoelectric properties are tested in a vibration‐detecting application. Both morphological observation and piezoelectric testing demonstrate that the electrowetting‐aided dry spinning helps in forming high‐quality polymeric piezoelectric fibers. Moreover, this method can also be applied in different fabrications, where adhesion between a liquid and solid surface needs to be enhanced. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43968.     

Effect of ionic liquid on the structure and desalination performance of PVDF-PTFE electrospun membrane

The relatively large pore size of electrospun membranes might limit their application for direct contact membrane distillation (DCMD). Incorporation of ionic liquid is a potential approach to decrease the pore size of electrospun membranes, which was attributed to the increased conductivity of electrospinning solution. In this study, a novel nanofibrous membrane based on the blends of poly(vinylidene fluoride) (PVDF), polytetrafluoroethylene (PTFE) and ionic liquid (BMIMPF₆) was fabricated and applied for the DCMD. The effects of the BMIMPF₆ on the morphology, pore size and DCMD performance of the PVDF-PTFE nanofibrous membrane were investigated. Compared with neat (PVDF-PTFE) membranes (average pore size: 0.93 μm), the incorporation of BMIMPF₆ resulted in a smaller mean pore diameter (0.58 μm). The liquid entry pressure value of the modified composite membrane also increased from 62.75 kPa (neat) to 83 kPa, due to the decreased pore size. The composite membrane exhibited a longer lifespan (about 26 h) than neat membrane during long-term DCMD process, which makes this composite membrane a promising candidate for DCMD application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48467.     

Anisotropic mechanical properties of hot‐pressed PVDF membranes with higher fiber alignments via electrospinning

By the use of a high‐speed collection drum, poly(vinylidene fluoride) (PVDF) was electrospun into aligned ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v), and a continuous hot‐press post‐treatment was performed on the membranes to improve their mechanical properties. Anisotropic tensile results and rupture behaviors of the hot‐pressed PVDF membranes with higher fiber alignments in both revolving direction (RD) and cross direction were obtained. It was found that, due to the true fracture of electrospun fibers and improvement of the interfiber compaction by hot‐press, the tensile strength and modulus of the hot‐pressed membranes in RD reached the highest values at 58.12 ± 4.46 MPa and 519.9 ± 34.1 MPa, respectively when the collection speed was 10.42 m/s. The decrease of porosity and liquid absorption also represented the compaction improvement of the electrospun fibrous membranes. The combination of fiber alignments and hot‐press could provide a novel method to fabricate high strength of electrospun membranes which have highly potential applications in filtration or battery separators. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Morphologies and electrical properties of electrospun poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyvalerate]/ multiwalled carbon nanotubes fibers

Electrospinning process was used to fabricate fine fibers from poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyvalerate] embedded with multiwalled carbon nanotubes (MWCNTs). Rotating disc collector was used to provide additional drawing force to stretch and align both the embedded MWCNTs and electrospun fibers themselves. Morphological observation revealed MWCNTs aligned to the fiber axis and protruding from the surface. To understand the electrical properties of the fiber, a single‐composite fiber has been deposited on a substrate, across multiple electrodes. Electrical conductivity of the single‐electrospun fiber with low MWCNT content of 0.2 wt % was calculated to be in a remarkable magnitude of about 2.07 Sm^?1. Electrical current flow spanning the fiber length of 1400 μm indicates that the presence of an interconnected network of MWCNTs exists within the fiber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

熔体微分静电纺PBAT纤维膜的制备工艺研究

探究了聚己二酸对苯二甲酸丁二醇酯（PBAT）熔体静电纺性能,并研究了熔体微分静电纺工艺参数与PBAT纤维性能之间的关系。结果表明,随着纺丝温度的升高,纤维直径减小,纤维直径分布呈先减小后增大的趋势;随着纺丝电压的升高,纤维直径减小且分布均匀,纤维膜力学性能逐渐提高;当纺丝距离为9 cm,纺丝温度为260 ℃,纺丝电压为45 kV时,制备的纤维细度及均匀度最佳,其直径为4.31 μm,直径分布标准差为0.76,纤维膜拉伸强度为9.9 MPa、断裂伸长率为111.2 %。     

Water filtration properties of novel composite membranes combining solution electrospinning and needleless melt electrospinning methods

New composite polyvinyl alcohol (PVA)/polypropylene (PP) membranes were prepared by combining both solution electrospinning and melt electrospinning methods. Self‐designed and made needleless melt electrospinning device was used to fabricate PP membranes which acted as the support layer. PVA membrane on the surface was fabricated via solution electrospinning. The electrospun PVA/PP composite membranes were characterized by the pore size distribution, pure water flux, and rejection ratio, then compared with general composite membranes. Characterizations revealed that the fiber diameter of solution electrospun PVA membrane and melt electrospun PP membrane were 0.171 ± 0.027 and 2.24 ± 0.33 μm, respectively, and the average pore size was 0.832 μm and 27.29 μm, which was much smaller than the nonwoven membrane. The rejection ratio to the 500 nm particles of the PVA/PP composite membrane could reach more than 96%, which was much larger than that of the PVA/non‐woven substrate of 90%, and the melt electrospun PP membrane of 80%, and still maintained high permeate flux of 32,346 L/m²h under the pressure of 0.24 bar. This approach of compositing the solution electrospun membranes and melt electrospun membranes could be useful in designing novel microfiltration membrane owning both higher flux and higher rejection ratio. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41601.     

Green synthesis of porous polyvinyl alcohol membranes functionalized with l-arginine and their application in the removal of 4-nitrophenol from aqueous solution

Green and single-step synthesis of porous poly(vinyl alcohol) membrane functionalized with l -arginine (PVA-g-Arg) is presented. Crosslinking, l -arginine functionalization and pore forming occurred simultaneously by a thermally induced process without using a crosslinker or an initiator. As-synthesized PVA-g-Arg membranes possessed a porous structure with an average pore size of 32–56 μm depending on the amount of l -arginine. The PVA-g-Arg were utilized as adsorbent membranes for the removal of 4-nitrophenol (4-NP) from aqueous solutions and demonstrated higher adsorption capacity than that of the unmodified PVA porous membrane. The pseudo-second-order described satisfactorily the kinetic adsorption of 4-NP by the membranes while the isotherms followed both the Langmuir and Freundlich models. The negative values of ΔG° and thermodynamic parameters confirmed that the adsorption of 4-NP by the PVA-g-Arg membranes was spontaneous and exothermic. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47835.     

One-step fabrication of superhydrophobic P(VDF-co-HFP) nanofibre membranes using electrospinning technique

In this study, superhydrophobic electrospun P(VDF-co-HFP) membranes were fabricated in a one-step electrospinning process. The effects of the key parameters of electrospinning (solution concentration, electrical potential, flow rate, and solvent) on the surface roughness, fiber formation, and hydrophobicity of the membranes were evaluated using Taguchi method. A 4 × 3 orthogonal array was utilized, and the results indicated that the solvent played the critical role in producing the superhydrophobic nanofibre membranes. It was demonstrated that it is possible to produce superhydrophobic membranes with P(VDF-co-HFP) without additional functionalisation and fillers. The highest water contact angle and the lowest contact angle hysteresis obtained were 156° and 5°, respectively, and the roughness values varied from 0.15 to 5.74 μm for the produced P(VDF-co-HFP) nanofibre membranes. The surface superhydrophobicity of the membranes was attributed to the specific structures consisting of a combination of beads and nanofibres. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48817.     

A super thin polytetrafluoroethylene/sulfonated poly(ether ether ketone) membrane with 91% energy efficiency and high stability for vanadium redox flow battery

In order to further decrease the cost and enhance the durability of sulfonated poly(ether ether ketone) membrane for vanadium redox flow battery, a super thin (40 μm) polytetrafluoroethylene (PTFE)/SPEEK (PS) membrane is prepared. The physico‐chemical properties and single cell performance of PS membranes prepared with different casting solvents including NMP (N‐methyl‐2‐pyrrolidone), DMF (N,N′‐dimethylformamide), and DMAc (N,N′‐dimethylacetamide) have been investigated. Results show that the energy efficiency of VRB with PS/DMF can reach up to 91.2% at the current density of 40 mA cm^?2, which is 11.1% and 6.4% higher than that of the commercial Nafion 212 and pristine SPEEK membrane, respectively. In addition, charge–discharge test over 150 times proves that the PS/DMF membrane possesses high stability and thus it is suitable for VRB application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43593.     

Organic–inorganic hybrid copolymer fibers and their use in silicone laminate composites

Nonwoven organic–inorganic fiber mats of poly(methyl methacrylate)‐graft‐poly(dimethyl siloxane) copolymers with various PDMS contents were produced by the electrospinning process. The average fiber diameter increased from 0.7 to 3 μm with increasing PDMS content. The fiber mats were used in the preparation of silicone‐laminated composite materials by distributing them (single, double and triple layer mats) in a silicone matrix prior to thermal curing. The composites showed a remarkably good fiber distribution in the silicone matrix. In general the stiffness and strength increased in the presence of fiber, and surprisingly, so did the toughness/extensibility. An interesting feature was that the most silicon‐rich fibers showed clear signs of yielding after tensile testing and failure. This, together with the greater compatibility of the fibers with the matrix because of the higher PDMS content, most probably favored composite toughness. All composite fracture surfaces were characterized by clear signs of fiber pull‐out. Fracture initiation areas were difficult to locate, and this is accredited to an even distribution of the individual fibers in the matrix. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

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     

Temperature‐sensitive PVDF hollow fiber membrane fabricated at different air gap lengths

This article describes preparation of temperature‐sensitive poly(vinylidene fluoride) hollow fiber membranes using the dry‐wet spinning technique and investigates effects of air gap length on the structures and performances. In spinning these hollow fibers, N,N‐dimethyl formamide and poly(ethylene glycol) (10,000) were used as the solvent and pore‐forming agent, respectively. The prepared fiber membranes were characterized by scanning electron microscopy, pore size measurement, filtration experiments of pure water flux, and solutes with different molecular weights. The fiber membranes exhibit a quite asymmetric structures consisting of double skin layers situated on the fiber walls, two finger‐like layers near skin layers as well as macrovoids and sponge‐like structures at the center of the fiber cross‐sections. Remarkable changes of pure water flux and retention of solute are observed around 32°C, indicating an excellent temperature‐sensitive permeability. As the air gap length increases, the pore size of fiber membrane decreases, which results in decrease of pure water flux and allows small molecules to permeate through the fiber membrane. POLYM. ENG. SCI., 53:2519–2526, 2013. © 2013 Society of Plastics Engineers     

Melt‐electrospinning of poly(ethylene terephthalate) and polyalirate

Rodlike polymer samples were made from three kinds of poly(ethylene terephthalate) (PET) pellets with different intrinsic viscosities (IV), and from polyalirate (Vectra) pellets. PET and Vectra fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device from these rodlike samples. The effects of IV value and laser output power on the fiber diameter of PET were investigated. Furthermore, the effect of the laser output power on the fiber diameter of Vectra was investigated. The crystal orientation of these produced fibers was also investigated by X‐ray photographs. The following conclusions were reached: (i) the diameter of PET fiber decreases with increasing laser output power; (ii) the minimum average diameter of PET fibers is scarcely influenced by the value of IV; (iii) the electrospun PET fibers show isotropic crystal orientation; (iv) fibers having an average fiber diameter smaller than 1 μm cannot be obtained from PET and Vectra using the system developed; and (v) preferred liquid crystal orientation can be seen in electrospun Vectra fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Surface modification of PVDF membranes with sulfobetaine polymers for a stably anti-protein-fouling performance

Two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA) were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane outside surface via chemical activation and atom transfer radical polymerization (ATRP). The ATRP time at 2 h under the 2 mol/L of zwitterionic monomers was the minimum period for the complete coverage of grafted sulfobetaine polymers on the PVDF membrane surface. The surface hydrophilicity of the sulfobetaine-modified PVDF membranes was significantly enhanced. The poly-MPDSAH-g-PVDF (GA: 247 μg/cm²) and poly-MEDSA-g-PVDF membranes (GA: 338 μg/cm²) efficiently resisted to the adsorption of both negative and positive charged proteins, and showed excellent anti-protein-fouling performance with flux recovery ratio (RFR) higher than 90% and total fouling (RT) less than 25% during the cyclic filtration of bovine serum albumin solution. After cleaned in membrane cleaning solution for 12 days, the grafted MPDSAH layer on PVDF membrane could maintain without change, however, the poly-MEDSA-g-PVDF membrane lost the grafted MEDSA layer. Therefore, the amide group of sulfobetaine, which made a great contribution to the higher hydrophilicity and stability, was significant in modifying the PVDF membrane for a stably anti-protein-fouling performance. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012