聚偏氟乙烯功能膜研究进展

聚偏氟乙烯(PVDF)机械性能、耐老化及耐化学腐蚀等性能优良,广泛应用于膜分离与膜过程领域,但其亲水性能差、易受污染使其在膜分离方面的应用受到限制,对其亲水性和抗污染性是目前研究的重要课题;其β晶型的特殊结构使PVDF具有优异的介电性、压电性和铁电性等,在介电材料、压电材料等领域应用愈来愈广,但晶型的多样性及聚集状态使得其电学性能不稳定,因此控制β晶相的含量及其有序聚集状态是能量存储和转换材料领域研究的前沿趋势。     

A novel poly(vinylidene fluoride) composite membrane for catalysis and separation

Timely separation of products from the reactant is a great challenge for a catalytic reaction process. In this study, we fabricated a novel poly(vinylidene fluoride) composite membrane with noble metal (Au, Ag, and Pd) nanoparticles in membrane pores to solve the faced challenge. The composite membrane has a unique structure comprising membrane surfaces with only PVDF and membrane pores with poly(methacrylic acid) microspheres coated by noble metal nanoparticles. The composite membrane is used for the catalytic reduction of p‐nitrophenol and the results indicate that the catalytic reaction can rapidly proceed. What is more, the product formed in reaction process can be immediately isolated from the reactant. Other drawbacks such as the easy aggregation and the difficult separation generally encountered by the metal nanocatalysts are also avoided by using the composite membrane. In operation process, the composite membrane shows good thermal, mechanical and catalytic stability. These attracted merits make the prepared composite membrane have desirable prospects in catalytic application. POLYM. ENG. SCI., 58:150–159, 2018. © 2017 Society of Plastics Engineers     

Grafting poly(vinyl amine-co-acrylic acid)s on poly(vinylidene fluoride) membranes

In this study, N-vinylacetamide (NVA) was graft-polymerized and graft-copolymerized with acrylamide (AAm) onto plasma-activated surfaces. The polymer compositions of the grafted layer were estimated from X-ray photoelectron spectroscopy spectra. N-vinylacetamide was enriched in the grafted polymers in all regions of the monomer compositions. The primary amine groups could be densely introduced on the surface by hydrolyzing the grafted poly(vinylacetamide-co-acrylamide). © 1994 John Wiley & Sons, Inc.     

Surface modification of polyamide and poly(vinylidene fluoride) membranes

Experimental results from the gas‐plasma treatment and electron‐beam irradiation of polyamide (PA) and poly(vinylidene fluoride) (PVDF) membranes to improve their wettability and to evaluate protein adsorption at their surface are presented. The wettability of the membrane surface was determined by contact angle measurements; the analysis of the surface composition was performed by X‐ray photoelectron spectroscopy (XPS). We observed that a reduction in the water contact angle was not always indicative of a reduction in the protein adsorption and, furthermore, that a charge at the surface of the modified membrane seemed to be a major factor in the protein adsorption process. Furthermore, the XPS results shed some light on the modification mechanism of PVDF and PA by electron‐beam irradiation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Protein immobilization onto poly (vinylidene fluoride) microporous membranes activated by the atmospheric pressure low temperature plasma

Hydrophobic poly (vinylidene fluoride) (PVDF) membrane surface was treated with atmospheric pressure low temperature plasma and investigated physical and chemical surface characterization. The contact angle of water on the exposed membrane surface was reduced with increasing of the treatment voltage and time, so indicates that the treatments can modify the PVDF membrane surface from hydrophobic to hydrophilic. In order to analyze the phenomenon in detail, the progress of defluorination including dehydrofluorination and oxidation reactions onto the surface was examined by X-ray photoelectron spectroscopy (XPS), and revealed the most effective treatment condition. The degree of grafting used acrylic acid monomer onto the surface has influenced with monomer concentration, reaction temperature and reaction time. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology. The membrane surfaces conjugated bovine serum albumin (BSA) as a protein were surely detected the nitrogen element contained with BSA.     

Preparation and characterization of antifouling poly(vinylidene fluoride) blended membranes

Poly(vinylidene fluoride) (PVDF) membranes have been widely used in microfiltration and ultrafiltration because of their excellent chemical resistance and thermal properties. However, PVDF membranes have exhibited severe membrane fouling because of their hydrophobic properties. In this study, we investigated the antifouling properties of PVDF blended membranes. Antifouling PVDF blended membranes were prepared with a PVDF‐g‐poly(ethylene glycol) methyl ether methacrylate (POEM) graft copolymer. The PVDF‐g‐POEM graft copolymer was synthesized by the atom transfer radical polymerization (ATRP) method. The chemical structure and properties of the synthesized PVDF‐g‐POEM graft copolymer were determined by NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. To investigate the antifouling properties of the membranes, we prepared microfiltration membranes by using the phase‐inversion method, which uses various PVDF/PVDF‐g‐POEM concentrations in dope solutions. The pure water permeabilities were obtained at various pressures. The PVDF/PVDF‐g‐POEM blended membranes exhibited no irreversible fouling in the dead‐end filtration of foulants, including bovine serum albumin, sodium alginate, and Escherichia coli broth. However, the hydrophobic PVDF membrane exhibited severe fouling in comparison with the PVDF/PVDF‐g‐POEM blended membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of novel poly(vinylidene fluoride) membranes using self-assembled dibenzylidene sorbitol for membrane distillation

We proposed a method for the preparation of novel poly(vinylidene fluoride) (PVDF) membranes with self-assembled 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS). The vapor-induced phase separation (VIPS) method with a dry/wet process was used to produce DMDBS/PVDF composite membranes. The resulting membranes exhibited the coexistence of PVDF cellular pores and crystalline particles. The DMDBS molecules self-assembled into nanofibril structures, and a large number of nanofibrils were found on the surfaces and in the cross-sections of the prepared membranes. The DMDBS nanofibril networks in the PVDF matrix acted as reinforcing materials that enhance the hardness and stiffness of the membranes. Moreover, because of the entangled DMDBS networks, a greater strain was required to induce sample failure; therefore, the ductility of the membranes increased with increasing amounts of DMDBS. In addition, in a membrane distillation process, our composite membranes exhibited a good permeate flux that was comparable to that of commercial PVDF membranes.     

Preparation of poly(vinylidene fluoride)/poly(methyl methacrylate) membranes by novel electrospinning system for lithium ion batteries

Fibrous membranes of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVdF/PMMA) were fabricated by electrospinning method with different concentrations of polymer solution: 14, 16, and 18 wt %. The morphology of the electrospun membranes was observed by scanning electron microscopy. The images revealed that the nanofibers showed uniform diameter and no bead formation was observed with the concentration of 16 wt %. Also, the structure, crystallinity, ionic conduction, and electrochemical stability of the electrospun membranes were characterized. The results suggested that electrolyte uptake, ionic conduction, and electrochemical stability were improved by the addition of PMMA. Furthermore, with the 16 wt % concentration of the polymer solution, the membrane showed a high ionic conductivity of 3.5 mS cm^?1 at room temperature and electrochemical stability of up to 5.1 V. We predicted that this new method may be very promising for preparing microporous PVdF/PMMA polymer electrolytes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Chlorinated poly(vinylidene fluoride)

Chlorinated poly(vinylidene fluoride) (PVF₂) was prepared by introducing chlorine gas into a CCI₄ suspension of PVF₂ at reflux temperature. Polymer crystallinity and softening point decrease, while solubility and adhesion increase with the degree of chlorination. In contrast to PVF₂, the chlorinated polymer is soluble in low-boiling common organic solvents, such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane. Chlorinated PVF₂ is resistant to dehydrochlorination and is thermally more stable than PVF, chlorinated PVF, PVC, or chlorinated PVC. Chlorinated PVF₂ coatings on wood, prepared by solution casting at room temperature, show outstanding weathering resistance.     

Crystallization of poly(vinylidene fluoride) by freeze-extracting method

Summary High crystallinity poly(vinylidene fluoride) (PVF₂) has been achieved by freezing its very dilute solution and followed by freeze-extracting the frozen solvent. FT-IR, WAXD, and DSC studies indicate that the freeze-extracted PVF₂ has higher crystallinity than those samples prepared by solution crystallization or by thermal annealing techniques.     

Proton exchange membranes based on poly(vinylidene fluoride) and sulfonated poly(ether ether ketone)

Blend membranes were obtained by solution casting from poly(vinylidene fluoride) (PVDF) and sulfonated poly(ether ether ketone) (SPEEK) in N,N-dimethylacetamide (DMAc). DSC and XRD were used to characterize the structure of the blend membranes. The effect of PVDF content on the membrane properties was investigated. The methanol permeability, water uptake and the swelling ratio of blend membranes decreased with the increase of PVDF content. Though the proton conductivity decreased upon the addition of PVDF, they were still comparable to that of Nafion^® 117 membrane. Higher selectivities were also found for most blend membranes in comparison with Nafion^® 117 membrane. The effect of methanol concentration on solution uptake, swelling ratio and methanol permeability of the blend membranes was also studied.     

Formation of multilayer poly(acrylic acid)/poly(vinylidene fluoride) composite membranes for pervaporation

Dual‐ and multilayer composite membranes, consisting of poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), were synthesized by the plasma‐induced polymerization technique. The dual‐layer membrane had a dense PAA layer grafted onto a microporous PVDF substrate, whereas in the multilayer membranes, the grafted PAA and the PVDF layers were arranged in an alternating sequence (e.g., PAA/PVDF/PAA and PAA/PVDF/PAA/PVDF/PAA). These membranes were used in a pervaporation process to separate ethanol–water solutions. For the dual‐layer membranes, the results indicated that the separation factor increased and the permeation flux decreased with increasing amounts of grafted PAA. For the case of grafting yield < 0.6 mg/cm², the composite membrane demonstrated poor separation. As the grafting yield reached 0.85 mg/cm², a sharp increase of the separation factor was observed. For the multilayer membranes, the pervaporation performances were very good, with high separation factors (on the order of 100) and reasonable permeation fluxes over a wide ethanol concentration range. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2266–2274, 2004     

Effect of surface modifying macromolecules on the properties of poly(vinylidene fluoride) membranes

Poly(vinylidene fluoride) (PVDF) membranes were surface-modified using fluorotelemer intermediate Zonyl BA-L as a fluorinated surface modifying macromolecules (SMM) additives in the concentration range from 0 to 2 wt.%. Prepared membranes were characterized by contact angle measurement, electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), and pervaporation test. The experimental results showed that SMM migrated to the surface and effectively increased the surface hydrophobicity of the PVDF membranes. The pure water permeation flux evaluated by pervaporation decreased with an increase in the content of SMM.     

Properties of poly(vinylidene fluoride)

The properties of fluorocarbon plastics have made them desirable for numerous new applications. Poly(vinylidene fluoride) (PVF₂) can be easily extruded into films or fibers or injection molded into a variety of shapes. It was found that crystallinity, molecular weight distribution and polymer structure are important in establishing resin properties. Highly crystalline PVF₂ with a narrow Gaussian molecular weight distribution gives specimens with optimum physical and chemical properties.     

氟化聚芳醚/PVDF复合阴离子交换膜的制备

为制备导电性能和机械性能良好的阴离子交换膜,将五甲基胍功能化的氟化聚芳醚二唑(FPAEO-G)与聚偏氟乙烯(PVDF)进行溶液共混制备了FPAEO-G/PVDF复合离子交换膜。考察了PVDF比例对复合膜的溶胀率、吸水率、离子交换容量(IEC)以及电导率等性能的影响。测试结果表明,PVDF共混比例为10%时,复合膜在室温(20℃)下的溶胀率为10.93%,吸水率是42.98%,离子交换容量(IEC)为1.54mmol/g,电导率为1.37×10-2S/cm。     

Effect of hot‐press on electrospun poly(vinylidene fluoride) membranes

Poly(vinylidene fluoride) (PVDF) was electrospun into ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v). The electrospun membranes were subsequently treated by continuous hot‐press at elevated temperatures up to 155°C. Changes of morphology, crystallinity, porosity, liquid absorption, and mechanical properties of the membranes after hot‐press were investigated. Results of scanning electron microscopy showed that there were no significant changes in fibrous membrane morphology when the hot‐press temperature varied from room temperature to 130°C, but larger pores were formed because of fibers melting and bonding under higher temperatures. Analyses of X‐ray diffraction and differential scanning calorimeter exhibited that the crystalline form of PVDF could transfer from β‐type to α‐type during hot‐press at temperatures higher than 65°C. Tensile tests suggested that the mechanical properties of the electrospun PVDF membranes were remarkably enhanced from 25 to 130°C, whereas the porosity and the liquid absorption decreased. The hot‐press at 130°C was optimal for the electrospun PVDF membranes. The continuous hot‐press post‐treatment could be a feasible method to produce electrospun membranes, not limited to PVDF, with suitable mechanical properties as well as good porosity and liquid absorption for their applications in high‐quality filtrations or battery separators. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Preparation and properties of poly (vinylidene fluoride) membranes via the low temperature thermally induced phase separation method

Tensile strength is of paramount importance to poly (vinylidene fluoride) (PVDF) membranes in expanding their industrial application. In this paper, porous PVDF membranes with higher tensile strength were prepared by the low temperature thermally induced phase separation (LT-TIPS) method. The effects of mixed diluents (MD) composition on the morphology, polymorphism, and tensile strength of such prepared flat sheet membranes were investigated. The competition of membrane formation mechanisms between the nonsolvent induced phase separation (NIPS) and TIPS was demonstrated by observing the membrane morphology in the LT-TIPS process. It was found that the tensile strength was improved by suppressing the formation of finger-like macrovoids and spherulitic morphologies through adjusting the composition of MD. PVDF crystallized into α phase for all the investigated cases, and as the MD became poorer, the total crystallinity increased slightly. Based on these experimental results, PVDF hollow fiber membranes were fabricated via LT-TIPS. The influences of MD composition and polymer concentration on the morphology, water permeability and tensile strength of the formed hollow fiber membranes were studied. The properties of optimized hollow fiber membranes associated with the surface and cross-section morphologies were promising and the performance can be further enhanced in future work.     

Crystallization kinetics of poly(vinylidene fluoride)

Specimens of poly(vinylidene fluoride) were crystallized isothermally at a series of temperatures in the vicinity of the melting point. The -form was the only crystalline polymorph present in the crystallized samples. Crystallization rates have been measured by differential scanning calorimetry. The results were analysed in terms of the Avrami equation. The rates of crystallization depend upon the undercooling and the data agree with a process of growth of spherulites controlled by a secondary surface coherent nucleation mechanism. The equilibrium melting temperature, the Avrami exponent, the free energy of formation of a nucleus of critical dimensions and the surfaces free energy of the lamellar crystallites were determined.     

Surface immobilization of polymer brushes onto porous poly(vinylidene fluoride) membrane by electron beam to improve the hydrophilicity and fouling resistance

Poly(vinylidene fluoride) (PVDF) membrane was pre-irradiated by electron beam, and then poly(ethylene glycol) methyl ether methacrylate (PEGMA) was grafted onto the membrane surface in the aqueous solution. The degree of grafting was significantly influenced by the pH value of the reaction solution. The surface chemical changes were characterized by the Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Combining with the analysis of the nuclear magnetic resonance proton and carbon spectra (¹H NMR and ¹³C NMR), PEGMA was mainly grafted onto the membrane surface. Morphological changes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The porosity and bulk mean pore size changes were determined by a mercury porosimeter. The surface and bulk hydrophilicity were evaluated on the basis of static water contact angle, dynamic water contact angle and the dynamic adsorption process. Furthermore, relative high permeation fluxes of pure water and protein solution were obtained. All these results demonstrate that both hydrophilicity and fouling resistance of the PVDF membrane can be improved by the immobilization of hydrophilic comb-like polymer brushes on the membrane surface.     

Preparation and characterization of porous poly(vinylidene fluoride) membranes for dehumidification with poly(ethylene glycol) as an additive

Porous poly(vinylidene fluoride) (PVDF) membranes for dehumidification were prepared from a PVDF/dimethylformamide/water system by phase inversion with poly(ethylene glycol) (PEG) as an additive at various concentrations (1.2, 1.8, and 2.4%) and with various molecular weights (1000, 2000, and 6000). The surface morphologies of the resultant membranes were characterized with scanning electron microscopy and atomic force microscopy, and the pore diameter, porosity, and pore size distribution of the membranes were also determined by a gas‐sorption method. The influence of the concentration and molecular weight of PEG on water‐vapor transport through the membranes was evaluated. The moisture‐transport property of the membranes was improved significantly with increases in the concentration and molecular weight of PEG, and a membrane with good moisture permeability was obtained with 2.4% PEG‐6000 as an additive. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010