PVDF Hollow Fiber Membranes Research Articles

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.

PVDF hollow fiber membranes prepared from green diluent via thermally induced phase separation: Effect of PVDF molecular weight

Poly(vinylidene fluoride) (PVDF) specimens of different molecular weights, along with tributyl O-acetyl citrate (ATBC) as green diluent, were used to prepare hollow fiber membranes by thermally induced phase separation (TIPS). By increasing the quenching bath temperature, the overall porosity increased and the tensile strength of the hollow fiber membranes decreased, whereas the washing temperature did not affect these properties. High molecular weight PVDF enhanced the mechanical properties and reduced porosity of the resulting hollow fiber membranes. Hollow fiber membranes were prepared with a very sharp pore size distribution and used for direct contact membrane distillation to demonstrate one of the potential applications of this membrane.

Absorption of CO2 Form Natural Gas via Gas-liquid PVDF Hollow Fiber Membrane Contactor and Potassium Glycinate as Solvent

PVDF hollow fiber membranes were fabricated using Thermally Induced Phase Separation (TIPS) method. Gas-liquid interface is formed at the pore openings adjacent to the liquid. In the membrane contactor module, gas diffuses from the gas side across the membrane and reaches the gas liquid interface where gas is absorbed and then reacted in the presence of solvent such as aqueous sodium hydroxide or amine solutions. Nowadays, Monoethanol amine (MEA) and Diethanolamine (DEA) are the most commonly used solvents. In the present work potassium glycinate is used as an alternative liquid absorbent. A comprehensive two-dimensional mathematical model was developed for the transport of carbon dioxide-methane gas mixture through the in lab-made hollow fiber membrane contactor. Potassium glycinate is found to be a promising liquid absorbent. Model predictions were validated with experimental data. Results revealed that mass transfer rate generally increased with the absorbent concentration and that aqueous potassium glycinate solution performs better than MEA and DEA. The model equations were solved using COMSOL software package, model predictions were in good agreement with experimental data.

Stability of acrylic acid grafted poly(vinylidene fluoride) hollow fiber membrane prepared by high‐energy electron beam

ABSTRACTIn this article, poly(vinylidene fluoride) (PVDF) hollow fiber membrane and acrylic acid (AA) were co‐irradiated by high‐energy electron beam to introduce hydrophilic carboxylic groups on the membrane surface. Thermal capability, mechanical performance, pore size, and permeation property were investigated to determine the stability of the membrane pore structure before and after irradiation polymerization. The decomposition temperature, melting point, glass transition temperature, and breaking force of the PVDF‐g‐AA membrane increased slightly because of irradiation grafting polymerization. After 15 months of storage, the pore size distribution of the PVDF‐g‐AA membrane became smaller and more dispersive. The pure water flux and the rejection to bovine serum albumin of the PVDF‐g‐AA membrane increased significantly with the increase in hydrophilicity and decrease in pore size. The results indicated that the structure and properties of the PVDF hollow fiber membrane were stable after high‐energy electron beam irradiation grafting polymerization, even after 15 months of storage. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41165.

Non-activation ZnO array as a buffering layer to fabricate strongly adhesive metal-organic framework/PVDF hollow fiber membranes.

A non-activation (NA) ZnO array is directly grown on a PVDF hollow fiber membrane. The defect-free MOF layers can be synthesized easily on the NA-ZnO array without any activation procedure. The array and MOF layers are strongly adhered to the hollow fiber membrane. The prepared ZIF membranes exhibit excellent gas separation performances.

열유도 상분리와 연신공정을 이용한 PVDF 중공사막의 제조

열유도 상분리와 연신공정을 이용한 PVDF 중공사막의 제조

Preparation of a PVDF hollow fiber blend membrane via thermally induced phase separation (TIPS) method using new synthesized zwitterionic copolymer

Antifouling properties of PVDF hollow fiber membrane were improved by the addition of a new synthesized zwitterionic copolymer. This copolymer was synthesized using methyl methacrylate and the zwitterionic monomer 3-(methacryloylamino)propyl-dimethyl(3-sulfopropyl) ammonium hydroxide) (MPDSAH). The copolymer was used as additive in the preparation of a poly(vinylidene fluoride) (PVDF) hollow fiber membrane via thermally induced phase separation. With addition of the copolymer, the crystallization temperature and spherulite growth rate of the polymeric solution decreased sharply. Quartz crystal microbalance with dissipation monitoring results showed that bovine serum albumin (BSA) interactions with the prepared PVDF/copolymer film sharply decreased with addition of the synthesized copolymer. BSA filtration results showed that the membrane had higher antifouling resistance than a membrane without the copolymer additive.

Fabrication of PVDF hollow fiber membranes: Effects of low-concentration Pluronic and spinning conditions

Due to the unique properties of amphiphilic Pluronic block copolymers, they have been blended with other polymers such as PVDF to prepare membranes. Considering the stability issue, the strong pore-forming ability of Pluronic F127, and the mechanical strength of the resultant membranes, Pluronic/LiCl mixed additive consisting of a very low concentration of Pluronic has been used in this study. The effects of spinning conditions on PVDF hollow fiber fabrication have also been studied. It is found that the use of merely 0.2wt% of Pluronic is sufficient to impose significant impacts on the morphology, filtration performance, and mechanical properties of the resultant fibers. Hollow fibers spun using higher coagulant temperature, higher take-up speed, and water as the bore fluid exhibit better mechanical properties and filtration performance. PVDF hollow fiber membranes with PWP of 1180L/m2hMPa and MWCO of 5kDa were obtained when spun with optimized spinning conditions and using 3wt% of LiCl and 0.2wt% of Pluronic as the mixed additive. The fibers can withstand a pressure of 0.55MPa from the lumen.

Preparation of Sulfobetaine-Grafted PVDF Hollow Fiber Membranes with a Stably Anti-Protein-Fouling Performance.

Based on a two-step polymerization method, 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 surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDF membrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDF membranes was significantly enhanced and the polyMPDSAH-g-PVDF membrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDF membrane, the polyMPDSAH-g-PVDF membrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDF membrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDF membrane could be maintain without any chang; however, the polyMEDSA-g-PVDF membrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDF membrane for a stable anti-protein-fouling performance via the two-step polymerization method.

Gas–liquid membrane contactor for ethylene/ethane separation by aqueous silver nitrate solution

Separation of light olefin from paraffin having the same carbon number is one of the most energy intensive separations in petrochemical processes, which uses very long distillation columns with very high number of trays. This is attributed to the very small differences in the relative volatilities. The purpose of this work is to study the absorption performance of a home-made PVDF hollow fiber membrane fabricated using thermally induced phase separation method. Separation of ethylene from an ethylene–ethane gas mixture, using a hollow fiber membrane based absorption–desorption system with aqueous silver nitrate as absorption solvent, and to enhance separation process with a purchased polypropylene hollow fiber membrane module used for stripping purposes. Experiments on the absorption of ethylene from ethylene–ethane mixture, into silver nitrate solutions were performed. The effects of initial ethylene concentration in feed gas, silver nitrate concentration in the inlet solvent, liquid and gas flow rates were investigated. Results reveal that ethylene/ethane separation factor increases with silver nitrate concentration and liquid flow rates. A two dimensional mathematical model was developed for this purpose. Model predictions were validated with experimental data. Model predictions were in good agreement with experimental results.

Physicochemical study of polyvinylidene fluoride–Cloisite15A® composite membranes for membrane distillation application

The effect of Cloisite15A® on the physicochemical properties of PVDF hollow fiber membranes was studied. The inclusion of Cloisite15A® in PVDF has a positive impact on the physicochemical properties of the membrane and significantly improves the DCMD performance.

PVDF hollow fiber and nanofiber membranes for fresh water reclamation using membrane distillation

Polyvinylidene fluoride hollow fiber and nanofibrous membranes are engineered and successfully fabricated using dry-jet wet spinning and electrospinning techniques, respectively. Fabricated membranes are characterized for their morphology, average pore size, pore size distribution, nanofiber diameter distribution, thickness, and water contact angle. Direct contact membrane distillation (DCMD) performances of the fabricated membranes have been investigated using a locally designed and fabricated, fully automated MD bench scale unit and DCMD module. Electrospun nanofibrous membranes showed a water flux as high as 36 L m−2 h−1 whereas hollow fiber membranes showed a water flux of 31.6 L m−2 h−1, at a feed inlet temperature of 80 °C and at a permeate inlet temperature of 20 °C.

Effect of TEP content in cooling bath on porous structure, crystalline and mechanical properties of PVDF hollow fiber membranes

Poly (vinylidene fluoride) (PVDF) hollow fiber membranes were prepared by adding triethyl phosphate (TEP) to the cooling water bath in a modified thermally induced phase separation process. The effect of TEP content in the cooling bath on the porous structure, crystallinity, thermal and mechanical properties of PVDF hollow fiber membranes was investigated. The melting temperature and crystallinity of the membranes were determined using differential scanning calorimetry. The crystalline and cross‐section morphology of the hollow fiber membranes were investigated using wide angle X‐ray diffraction and scanning electron microscopy. The resulting membrane exhibited a nearly symmetric structure. The results showed that the TEP content in the cooling bath had a crucial role on the membrane formation, which was also confirmed from the morphology and mechanical properties of the hollow fibers. The porosity, average pore size, crystallinity, Young's modulus, max stress, and elongation at breakage of the hollow fiber membranes can be related to the amount of TEP in the cooling bath. Better pore connectivity was obtained in hollow fiber membranes when the weight ratio of TEP to water was 40:60. POLYM. ENG. SCI., 54:2207–2214, 2014. © 2013 Society of Plastics Engineers

Preparation and Characterization of Poly(Vinylidene Fluoride) Hollow Fiber Membranes via Modified Thermally Induced Phase Separation Process

Poly (vinylidene fluoride) (PVDF) hollow fiber membranes were successfully prepared using DMAc/γ-BL as the mixed diluent and PEG as the additive through modified thermally induced phase separation (M-TIPS) process. The membranes prepared were characterized by scanning electron microscope. Their properties such as water permeability and mechanical properties were also determined. The results show that PVDF membranes have spherical crystallites structure with interconnected network structure because of the combination of solidliquid and liquid-liquid phase separation. When using 25wt% aqueous ethanol solution as the coagulation, the PVDF hollow fiber membrane shows the tensile strength, i.e.4.59MPa and pure water flux, i.e.415 L/ (m2·h).

Study on coupling with catalytic wet air oxidation and membrane separation in the treatment of cationic red GTL

Coupling with the advantages of catalytic wet air oxidation (CWAO) and membrane separation under room condition, a new type of integrated fluidized-bed reactor was designed, with a PVDF hollow fiber membrane module submerged in. Its performance was investigated by the simulation of catalytic degrading cationic red GTL wastewater with initial concentration of 50 mg/L. The experimental results showed that the decolorization of cationic red GTL rose with the increase in residence time, the dosage of Mo/Zn/Al/O catalysts and aeration intensity, whereas it decreased against the increase in pH value. The optimal conditions of residence time catalyst dosage, pH value, and aeration intensity were 1.5 h, 1.5 g, 4, and 0.036 m3/h, respectively. The decolorization efficiency was above 98%, and TOC removal efficiency was more than 67%, which were apparently superior to the performance of single CWAO process in the batch test, and moreover, the interception efficiency on catalyst was approximately 100%. It can be found from the FT-IR analysis of original influent and effluent of membrane that the bonds of C=C, C–N as well as N=N were destroyed, while new bonds of C=O, –NO3, and N–H were formed. The BOD/COD ratio of the treated effluent been improved from 0.05 to 0.41.

Microporous polyvinylidene fluoride hollow fiber membrane contactors for CO2 stripping: Effect of PEG-400 in spinning dope

In order to develop the structure of microporous PVDF membranes, PEG-400 was introduced into the polymer dope as a non-solvent additive. The hollow fiber membranes were prepared via a wet phase-inversion process and then used in the membrane contactor modules for CO2 stripping from water. By addition of different amounts of PEG-400, cloud points of the polymer dope were obtained to examine phase-inversion behavior. From FESEM analysis, the membrane structure changed from a finger-like to an approximately sponge-like morphology with the addition of 4wt.% of PEG-400. The prepared membranes presented smaller mean pore size (0.13μm) and significantly higher wetting pressure (550kPa) compared to the plain membrane. From CO2 stripping test, at water velocity of 0.4m/s, the PVDF membranes prepared by 4% PEG-400 demonstrated an approximate CO2 stripping flux of 4.5×10−5(mol/m2s) which is 125% higher than the flux of the plain membrane. It could be concluded that structurally developed hydrophobic PVDF hollow fiber membranes can be prepared by a controlled phase-inversion process to enhance the performance of gas–liquid membrane contactor.

Dry–wet spinning of temperature-sensitive PVDF hollow-fiber membranes at different bore fluid flow rates

In this work, dry–wet spinning was conducted to fabricate poly(vinylidene fluoride)-g-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAm) copolymer hollow-fiber membranes. The effect of the bore fluid flow rate (BFFR) on the structure and performance of each hollow-fiber membrane was investigated by X-ray photoelectron spectroscopy (XPS), field emission scan electronic microscopy (FESEM), pore-size measurements, mechanical property evaluations, and a filtration experiment. It was found that the grafted PNIPAAm chains aggregated on the inner surface of the fiber membrane due to the effect of the bore fluid. When the permeation temperature was increased from 20 to 45 °C, a drastic reduction in the pure-water flux and a remarkable increase in the retention of bovine serum albumin (BSA) were observed at around 32 °C, indicating that the as-prepared fiber membranes exhibit excellent temperature sensitivity. Pore-size measurements confirmed that both the mean pore size and the porosity increase with increasing BFFR, endowing the fiber membranes with high pure-water fluxes and low retentions of BSA.

Surface modification of PVDF hollow fiber membrane and its application in membrane aerated biofilm reactor (MABR)

A novel composite hollow fiber membrane for membrane aerated biofilm rector (MABR) was prepared by coating L-3,4-dihydroxyphenylalanine (DOPA) on the surface of PVDF membrane. MABR process study was conducted to test the performances of the original and modified membranes for 166 days. The results indicate that coated membrane showed 2 times higher gas flux, lower water contact angle (declined from 86.5° to 52°), and significantly improved surface roughness. The modified membrane displayed an excellent MABR performance. Its COD, NH4(+)-N and TN removal efficiencies were kept above 90%, 98.8% and 84.2% during the first 4-month experiment. By tracking experiment at 0.01 MPa, to achieve COD removal efficiency of 85.9%, half an hour is required with the modified membrane, instead of 6h using the original one. Besides, faster NH4(+)-N and TN removal at 0.01 MPa were also achieved with DOPA composite membrane.

Surface modification of PVDF hollow fiber membrane to enhance hydrophobicity using organosilanes

AbstractThis work investigates the membrane modification to enhance hydrophobicity aiming for applications as membrane contactors. The PVDF membranes were activated by NaOH and by plasma activation followed by grafting using three organosilanes. For the NaOH, the contact angle of original membranes (68°) was decreased from 44° to 31° with increasing NaOH concentration from 2.5M to 7.5M at 60°C for 3 h. The contact angle of NaOH treated membranes was increased to 100° after modification with 0.01M FAS‐C8 for 24 h. A needle‐like structure was observed on the membrane surface while there was no significant change in pore size and pore size distribution. Moreover, FTIR and XPS data showed Si peak and composition. The mechanical strength was improved. The surface modified membranes under helium plasma activation followed by grafting with 0.01M FAS‐C8 for 24 h showed higher contact angle, mechanical strength and surface roughness than that obtained by NaOH activation method while other physical properties did not change. The long‐term performance test for 15 days of operation was conducted. The modified membranes exhibited good stability and durability for CO2 absorption. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Fabrication and characterization of antibacterial PVDF hollow fibre membrane by doping Ag-loaded zeolites

This work describes the fabrication and characterization of antibacterial poly(vinylidene fluoride) (PVDF) hollow fibre membranes via phase inversion using dry-jet wet-spinning technique. Ag-loaded NaY zeolites were particularly synthesized and then doped with PVDF spinning solution to produce a novel antibacterial hollow fibre with enhanced antibacterial efficiency. The morphologies, crystal structures, and Ag+ loading of synthesized Ag-loaded NaY zeolites were analyzed by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. The antibacterial efficiencies of the prepared hollow fibre membranes against Escherichia coli (E. coli) were evaluated by halo zone test, E. coli suspension filtration test and adhesion test. The surface morphologies, pure water flux, hydrophilicity, tensile strength, through-pore size, resistance to BSA of antibacterial PVDF hollow fibre membrane were also investigated. All results demonstrated that PVDF hollow fibre fabricated by doping Ag-loaded zeolites showed excellent antibacterial property, high permeability and mechanical strength, indicating the promising application as the antibacterial ultra-filtration membranes.