聚偏氟乙烯微孔膜制备方法研究进展

介绍了浸没沉淀法、热致相分离法以及蒸发助热致相分离法制备聚偏氟乙烯(PVDF)微孔膜的研究进展.重点介绍了溶剂、凝固浴组成、凝固浴温度、添加剂和蒸发时间等因素对浸没沉淀法制备PVDF膜的影响,并对制备PVDF膜的发展提出建议和展望.同时简单介绍了PVDF微孔膜的亲水性改性.     

Innovative hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride (PVDF) composite membrane for vacuum membrane distillation

Though membrane distillation (MD) has gained more and more attention in the field of desalination, the wetting phenomenon was still a non-negligible problem. In this work, a method combined dip-coating and UV in situ polymerization for preparing hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride composite membranes. This composite membrane consisted of a top thin hydrophobic coating layer and hydrophilic substrate membrane. In terms of anti-wetting properties, contact angle and liquid entry pressure of all composite membranes (except for those based on 0.45 μm) exceeded 160° and 0.3 MPa, respectively. In particular, the desalination performance was tested in vacuum membrane distillation tests by feeding 3.5% (mass) saline solution (NaCl) at 60 ℃. The composite membranes with larger support pore size and lower PFPE content had higher membrane distillation flux. And for stability tests (testing the 0.22 μm membrane coated by 5% (mass) PFPE), the highest MD flux 29.08 kg·m^-2·h^-1 and stable salt rejection (over 99.99%) during the period. Except that, the effects of coating material concentration and pore sizes of substrate membrane were also investigated for surface morphology and topography, porosity, mechanical strength and pore size characteristics. This work provided a simple and effective alternative to prepare excellent hydrophobic composite membranes for MD applications.     

Morphological study of poly(vinylidene fluoride) asymmetric membranes: Effects of the solvent,additive, and dope temperature

Asymmetric poly(vinylidene fluoride) (PVDF) membranes were cast with commercial‐grade Kynar K760 polymer pellets and four different solvent systems: N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide, 1‐methyl‐2‐pyrrolidone, and triethyl phosphate. With a focus on the PVDF/DMAc system, the effects of various additives (i.e., ethanol, glycerol, lithium chloride, lithium perchlorate, and water) on the resulting membrane morphology were investigated. The membrane morphology was examined with scanning electron microscopy. The effect of the dope solution temperature on the membrane morphology was also studied for the various additives used. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1782–1789, 2004     

Preparation of antibacterial polyvinylidene fluoride (PVDF) ultrafiltration membranes with direct addition of N-halamine polymers

In this study, novel antibacterial ultrafiltration polyvinylidene fluoride (PVDF) flat sheet membranes were produced with addition of synthesized N-halamine polymers. The ternary phase diagrams of PVDF and the synthesized polymers with N-methyl-2-pyrrolidone and water systems were prepared. The water flux and BSA rejection performances of the produced membranes were assessed both with and without PVP addition, and compared with a commercial membrane. The produced membranes were characterized with FTIR, XPS, DSC, and SEM analysis. Addition of N-halamine polymers to the membrane structure significantly improved the biocidal performance of the produced membranes against Staphylococcus aureus and Escherichia coli (10⁵ CFU).     

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.     

Effect of solvents on morphology and polymorphism of polyvinylidene fluoride membrane via supercritical CO2 induced phase separation

Poly vinylidene fluoride (PVDF) membranes were prepared via supercritical CO₂ induced phase separation. The effects of solvent power on PVDF membrane morphology and polymorphism were investigated using N‐N‐dimethylformamide (DMF), triethyl phosphate (TEP), and their mixture respectively. The morphology evolution including cross‐section and surfaces were thoroughly studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). The differences of solubility parameters between the solvent and PVDF affected the phase separation and the resultant morphology. The various crystalline phases of the membranes were mainly investigated by Fourier transform infrared spectroscopy (FTIR) and X‐ray diffractometer (XRD). Solvent with larger dipole moment tended to form polar β phase. Decreasing the difference of solubility parameters favored the formation of α phase. Furthermore, the effects of salt additive on PVDF membrane morphology and crystalline form were studied as well. Results turned out that lithium chloride (LiCl) induced a porous top surface and boosted the formation of β phase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41065.     

Nano SiO2 and TiO2 embedded polyacrylonitrile/polyvinylidene fluoride ultrafiltration membranes: Improvement in flux and antifouling properties

Polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) ultrafiltration (UF) membranes are widely used in drinking water and wastewater applications. These membranes are prone to fouling and membrane efficiency decreases with time under constant operation. Significant improvements/modifications are necessary to apply these polymers as sustainable membrane materials. In this study, PVDF and PAN UF membranes were modified through incorporation of nanoparticles (NPs) namely SiO₂ and TiO₂. PVDF and PAN UF membranes were prepared by phase inversion method from polymer solutions having dispersed SiO₂ and TiO₂ NPs in it. Membrane surface hydrophilicity, charge, roughness, and morphology were studied. Equilibrium water content and molecular weight cut-off of the membranes were also measured. Addition of NPs increased membrane surface hydrophilicity, equilibrium water content, and surface potential. NPs modified membranes exhibited better membrane flux (35–79% higher) and antifouling properties (flux recovery ratio values 28–41% higher) than the virgin membranes.     

聚偏氟乙烯膜亲水改性研究进展

聚偏氟乙烯以其优异的力学性能和化学性能被广泛用于制备微滤膜、超滤膜、纳滤膜和反渗透膜等水处理膜材料,然而由于其极强的疏水性,使其在用于水处理过程中存在通量低和容易被污染等缺陷,这极大地降低了水处理效率和薄膜的使用寿命,因此对其亲水改性具有重要的实际意义。本文根据改性方法的异同,将近几年来国内外对聚偏氟乙烯膜的亲水化改性研究工作按共混改性、共聚改性、表面接枝改性和表面涂覆改性等方法进行了综述,通过不同改性方法对聚偏氟乙烯水处理膜的亲水效果、渗透能力和防污染性等方面的影响,着重比较讨论了各种改性方法的改性效果及优缺点。最后对未来聚偏氟乙烯膜的亲水改性研究及工业化应用的发展趋势进行了展望。     

Highly porous electrospun polyvinylidene fluoride (PVDF)-based carbon fiber

Porous poly(vinylidene fluoride) fibers were prepared by electrospinning from solutions in dimethylformamide, poly(ethylene oxide) (PEO) and water. The PVDF fiber mats were then converted into electrospun carbon fiber paper using a low temperature chemical stabilization treatment (“dehydrofluorination”) followed by carbonization at 1000 °C. The resulting self-supporting carbon fiber paper exhibits unusually high surface area, in excess of 380 m²/g as measured by the nitrogen adsorption method, and a hierarchical pore structure. The largest pores are formed by the interstices between fibers; intermediate-sized pores arise from liquid–liquid phase separation during electrospinning to form polymer-rich and solvent-rich domains within the fibers; the smallest pores form upon decomposition of the PEO during carbonization. The electrospun carbon paper performs well as an electrode for driving the redox chemistry of ferrocene/ferrocenium. This is attributed to the high surface area of the electrode and the ease of diffusion of the redox-active species within the porous structure. The ratio of the dehydrofluorination agent (1,8-diazabicyclo[5.4.0]undec-7-ene) to vinylidene fluoride during dehydrofluorination was found to be the key to retaining the as-spun pore morphology during carbonization. The structure and morphology were further characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray diffraction, and Raman spectroscopy.     

Synthesis and characterization of polymeric nitrocellulose membranes: Influence of additives and pore formers on the membrane morphology

The control of the membrane surface and cross‐section morphology is extremely important in the enhancement of the wicking and binding ability of the lateral flow membrane, which is one of the processing materials in medicine and health care analysis devices. The lateral flow rate and protein‐binding performance is based on the thin layers of the membrane. The challenge of this study was to combine the influences of additives and pore‐former materials to obtain a thin lateral flow nitrocellulose membrane with controlled membrane morphologies. Water was found to be an effective pore former for enhancing the porosity and pore size of the membrane. However, too high of a water content increased the surface roughness and decreased the membrane protein‐binding ability. Different properties of the individual plasticizers/additives contributed to the disparity of membrane performance in binding and solute lateral wicking time. The correlations between the effects of additives and pore former toward the final membrane structure and performance of the membrane‐forming system are discussed extensively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly(vinylidene fluoride) (PVDF) membranes for fluid separation

The importance of poly(vinylidene fluoride) (PVDF) as a membrane material has long been recognised in many membrane processes. Compared to other types of polymeric membranes, the PVDF membranes have received great attention because of its outstanding properties including high hydrophobicity, thermal stability, chemical resistance and excellent mechanical strength. This article provides an overview of recent development in PVDF membrane processes, focussing on the commercial PVDF membrane products for water and wastewater treatment and possible applications of PVDF membranes in areas such as membrane based gas absorption and membrane distillation where no substantial commercial PVDF membrane processes are available so far.     

Poly(vinylidene fluoride) fibrous membranes doped with polyamide 6 for highly efficient separation of a stable oil/water emulsion

Ideal membranes toward separation of stable oil/water emulsions should have surface hydrophilicity and submicron pores in the separating layer. However, electrospun membranes made from poly(vinylidene fluoride) (PVDF) cannot meet these requirements, failing to remove oil droplets from a stable oil/water emulsion. By doping with a certain polyamide 6 solution, surface hydrophilicity, and interconnected pores with submicron size are successfully achieved. As a result, separation of a stable emulsion with an efficiency above 99% is exhibited by the modified PVDF membranes. Moreover, underwater oleophobicity of the modified PVDF membranes imparts them with good antifouling performance. The modified PVDF membranes could have great potentials in practical stable oil/water emulsion separation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44980.     

Resistivity behaviour of barium titanate (BaTiO3)/polyvinylidene fluoride (PVDF) composites

The resistivity behaviour of Barium Titanate (BaTiO₃) / Polyvinylidene Fluoride (PVDF) composites studied by changing the wt. fraction of BaTiO₃. The resistivity behaviour of composites followed that of PVDF up to 50% wt. fraction of BaTiO₃ in the composite. The resistivity of the composite with 70% wt. fraction of BaTiO₃ varied one order. The results are correlated with SEM studies on the composites. At a lower wt. fraction of BaTiO₃ in composites, PVDF formed an insulating layer over BaTiO₃ grans, which is not significant at higher wt. fractions of BaTiO₃ in the system     

Development of mesoporous titanium dioxide hybrid poly(vinylidene fluoride) ultrafiltration membranes with photocatalytic properties

A photocatalytic activity ultrafiltration membrane (UFM) was prepared by the blending of a poly(vinylidene fluoride) (PVDF) polymer with mesoporous titanium dioxide (M‐TiO₂) particles via the phase‐inversion method. The microstructure of the membrane and Ti element distribution were characterized by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Their properties were also determined by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, tensile stress tests, contact angle tests, bovine serum albumin retention, water flux, and permeation flux. When the M‐TiO₂ concentration reached 1 wt %, the thermal stability, mechanical properties, hydrophilicity, flux, and antifouling performance of the M‐TiO₂/PVDF UFM were improved to an optimal value with the M‐TiO₂ particles successfully entrapped and evenly distributed throughout the PVDF polymer matrix. Compared with the P25‐modified PVDF UFM (1 wt %), the M‐TiO₂‐modified PVDF UFM (1 wt %) exhibited better photocatalytic activity and wonderful stability in the UV photocatalytic degradation of the organic dye Rhodamine B. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43427.     

Fabrication and properties of PVDF and PVDF‐HFP microfiltration membranes

Poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) were used to fabricate porous microfiltration membranes via a thermally induced phase separation (TIPS) method, and dibutyl phthalate (DBP) was used as diluent. The effects of polymer concentration on structure and performance were studied in detail. In addition, the effect of incorporation of hexafluoropropylene (HFP) groups on the membrane was also investigated. The formation mechanism was proposed with the assistance of a phase diagram. The results showed that the incorporation of HFP groups resulted in a lower crystallization temperature (T_c) of the polymer/DBP system. In addition, the porosity, pure water flux, and ink solution flux decreased with increasing polymer concentration. In contrast, the water contact angle, ink rejection ratio, and mechanical properties had an increasing tendency. When the polymer concentration was 30 wt %, the obtained membrane was most suitable for microfiltration. Furthermore, the incorporation of HFP groups improved the properties of the obtained membrane, including better hydrophobicity, mechanical properties, antifouling property, and chemical resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46711.     

Inherent porous structure modified by titanium dioxide nanoparticle incorporation and effect on the fouling behavior of hybrid poly(vinylidene fluoride) membranes

The incorporation of nanoparticles (NPs) into a casting solution is a widely used practice for controlling the membrane fouling tendency, but the specific role of NPs in fouling control from an internal porous structure optimization has seldom been investigated. In this study, we evaluated the specific role of titanium dioxide (TiO₂)–NPs (Degussa P25) in mitigating membrane organic fouling. We prepared the membranes by tailoring the concentrations of the NPs well; this resulted in an optimized membrane microstructure consisting of fingerlike voids (beneath the skin layer of the membrane) and spongy voids (adjacent to the fingerlike voids). The NP incorporation induced the formation of spongy voids beneath the skin layer, and the increase in the NP concentration increased the formation of spongy voids. Moreover, surface images obtained by scanning electron microscopy, X‐ray photoelectron spectroscopy results, and contact angles confirmed that TiO₂–NPs were almost absent on the skin layer. Antifouling experiments were performed with a model organic foulant in two flow orientations [fingerlike voids facing the retentate (FVR) and spongy voids facing the retentate (SVR)]. The results show that the membrane fluxes in FVR decreased more than those in SVR. The membrane with 1.5 wt % TiO₂ operated in SVR exhibited the lowest flux decline; this suggested that spongy voids with TiO₂ exposure could mitigate fouling to a greater extent. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43265.     

Influence of additives on the morphology of PVDF membranes based on phase diagram: Thermodynamic and experimental study

In the present study, the morphology of asymmetric poly(vinylidene fluoride) blend membranes which were prepared by the phase inversion method is rationalized by comparing two non‐dimensional number represent thermodynamic and kinetic properties of the prepared membrane. These two parameters change phase diagram and demixing rate between solvent and nonsolvent. TiO₂ nanoparticles and polyvinylpyrrolidone were used as additives. Hansen solubility parameters of the components are calculated by Van Krevelen method. Furthermore, kinetic and thermodynamic properties of the prepared solutions are determined by drawing phase diagrams and controlling mass transfer rate during precipitation of casting solution. Besides, to further analyze different tests encompass; permeability, rejection, porosity, pore size determination, contact angle, and field emission scanning electron microscopy images were carried out. It is shown, additives as pore former induced higher permeability and porosity, however, at higher concentration of additives high viscosity obstacle mass transfer and sponge‐like morphology is obtained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46225.     

Synthesis and characterization of cellulose triacetate and poly(ethylene imine) membranes containing a polyether macrobicyclic: Their application to the separation of copper(II) and silver(I) ions

A cellulose triacetate (CTA)–poly(ethylene imine) (PEI) membrane containing a polyether macrobicyclic (cryptand) as a carrier and 2‐nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The CTA–PEI–cryptand–NPOE membrane was characterized with chemical techniques as well as Fourier transform infrared, X‐ray diffraction, differential scanning calorimetry, and scanning electron microscopy. The permeation of silver and copper ions through the CTA–PEI–cryptand–NPOE membrane was comparable to that through a supported liquid membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1401–1410, 2004     

Morphology and performance of poly(vinylidene fluoride) flat sheet membranes: Thermodynamic and kinetic aspects

In this study, poly(vinylidene fluoride) (PVDF) membranes were prepared using two different solvents with various polymer concentrations to investigate the predominant kinetic or thermodynamic aspects of membrane preparation in a phase separation process. For this purpose, dimethyl sulfoxide (DMSO) as a weak solvent and N‐2‐methylpyrrolidone (NMP) as a strong solvent were used with polymer concentrations between 8 and 15 wt %. Scanning electron microscopy and water content, contact angle, and pore size measurements were used to assess the factors affecting the physicochemical properties of the prepared membranes. The results showed that in the case of NMP, the membrane structure is mainly controlled by thermodynamic parameters, while when using DMSO, kinetic parameters are predominant. According to the results, the prepared PVDF‐based membranes with DMSO exhibited a relatively denser top layer and less permeation compared to the NMP/PVDF membranes. The difference between the viscosities of the casting solutions with equal polymer concentrations in DMSO and NMP was considered to be the main effective factor in solvent/nonsolvent exchange, resulting in denser top layers in the DMSO/PVDF membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46419.     

Effect of coagulation medium on properties of sulfonated polyvinylidene fluoride membranes

The performance and the structure of sulfonated polyvinylidene fluoride membranes prepared in different coagulation media were investigated. Several pure organic compounds and mixtures of some of them with water were used as coagulation media. The membrane were tested in an ultrafiltration laboratory unit with dextran aqueous solutions. The overall structure of the membranes was examined with the aid of the scanning electron microscope. The effect of temperature of the coagulation medium on the properties of the membranes were also investigated.