Morphological, Electrical, and Chemical Characteristics of Poly(sodium 4-styrenesulfonate) Coated PVDF Ultrafiltration Membranes after Plasma Treatment (original) (raw)
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Effect of poling time on filtration properties of PVDF membranes treated in intense electric fields
Polymer Bulletin, 2014
It was found that treatment in intense electric fields (i.e., electrical poling) changed the microstructure and filtration performance of polyvinylidene fluoride (PVDF) microfiltration membranes. The effect of temperature, sample size and time on the electrical breakdown of membranes was studied. It was shown that the hydraulic permeability and flux of the membranes can be tuned by changing the poling time. The effect of electrical poling on rejection and molecular weight cutoff was more significant. It was also found that the electrical breakdown of PVDF membranes is a gradual process and a long exposure time to an intense electric field can have adverse effects on the separation performance of the membranes.
2012
This work describes the synthesis of charged poly(vinylidene fluoride) (PVDF) membranes. Cationic membranes were prepared by graft modification using radiation-induced polymerization. Glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EDMA) were used as monomers and after graft polymerization the former was sulfonized with sodium sulfite. Membrane characterizations were carried out by FTIR-ATR, SEM-EDS, ionic exchange capacity, hydraulic permeability and liquid-liquid displacement. FTIR-ATR and SEM-EDS analysis revealed that increasing grafting degree increased the amount of the sulfonic group in the membranes. Sulfonated membranes showed smaller pore sizes and higher pore density than the original PVDF membrane. Oil/water ultrafiltration tests with the charged PVDF membranes showed interesting permselectivity performance; high oil retention values (R > 98%), low chemical oxygen demand in the permeate solution (COD < 59 mg L −1 ). In addition, low fouling (<16.6%) and negligible irreversible fouling of the charged membranes was observed during the ultrafiltration tests.
Preparation of PVDF UF Membranes under an External Electric Field with PVP as Additive
Journal of Membrane and Separation Technology, 2014
In this study, PVDF UF membranes were prepared with PVP as additive via a favorable method of applying high voltage external electric field (2kV) through the immersion precipitation phase inversion process. The influence of external electric field on the structure, surface functional groups, membrane potential, and surface hydrophilicity of the membranes were researched. In addition, anti-fouling property and separation performance of the membranes were also investigated. The results indicated that the protein adsorption amount on the electric treated membranes was distinctly reduced. Especially for the electric treated PVDF membrane with PVP K70 as additive, the value of water contact angle reached 75.4° and the protein adsorption amount decreased 76 %, reaching 20.39 g cm-2. The separation performance of the electric treated membrane was also superior to that of the untreated membrane. All the experimental results indicated that this electric treated approach open a promising way for the modification of PVDF membrane because it combined membrane preparation and modification in only one physical step without additional chemical reagents.
Journal of Applied Polymer Science, 1995
Polyethersulfone ultrafiltration membranes (MWCO: 9000, 35,000 and 85,000) were surface modified by preadsorption of poly(sodium 4-styrenesulfonate) (PSS) upon the permeation of aqueous solution of the polymer for about 100 min. Membranes with lower MWCO values were modified primarily on the top surface, whereas high MWCO membranes were modified both on the surface and pore walls as well. The IR spectra of surface modified membranes show absorption bands at 1040 cm −1 due to symmetric vibration of SO 3 − group, and at 2925 and 2852 cm −1 corresponding to asymmetric and symmetric stretchings, respectively, of aliphatic (backbone CH 2 and CH) unit present in PSS. Surface modified membranes have shown separations of 28-56% for Na 2 SO 4 , 11-19% for NaCl and <5% for CaCl 2 with water permeation rates of 35-102 lm h at 2 kg/cm 2 when tested for 500 ppm feed solution. The rejection of Na 2 SO 4 decreases in an exponential manner when the concentration of Na 2 SO 4 in the feed solution was increased from 500 to 2500 ppm, which is a characteristic of negatively charged membranes. The antifouling nature of unmodified and surface modified membranes were compared by ultrafiltration of aqueous solutions of different molecular weight polyethylene glycols and dextrans. Surface modified membranes have shown better antifouling properties compared to unmodified membranes, as indicated by flux decline with operating time.
Characteristics of PVDF Membranes Irradiated by Electron Beam
Membranes, 2015
Polyvinylidene fluoride (PVDF) membranes were exposed vertically to a high energy electron beam (EB) in air, at room temperature. The chemical changes were examined by Fourier Transform Infrared Spectroscopy (FTIR). The surface morphologies were studied by Scanning Electron Microscopy (SEM) and showed some changes in the pore size. Thermogravimetric (TGA) analysis represented an increase in the thermal stability of PVDF due to irradiation. Electron paramagnetic resonance (EPR) showed the presence of free radicals in the irradiated PVDF. The effect of EB irradiation on the electrical properties of the membranes was analyzed in order to determine the dielectric constant, and an increase in the dielectric constant was found on increasing the dose. The surface hydrophilicity of the modified membrane was characterized by water contact angle measurement. The contact angle decreased compared to the original angle, indicating an improvement of surface hydrophilicity. Filtration results also showed that the pure water flux (PWF) of the modified membrane was lower than that of the unirradiated membrane.
Characteristics of a PVDF–Tin Dioxide Membrane Assisted by Electric Field Treatment
Membranes
Polymeric membranes have good properties for filtering water. In this paper, a membrane made from polyvinylidene fluoride (PVDF) polymer with 15 wt%, 17.5 wt%, and 20 wt% polymer content, with the addition of 1 wt% of tin dioxide with electric field treatment, is presented. The electric field used was DC 15,000 V. The membrane was tested to determine its characteristics and properties. The physical properties were examined with a scanning electron microscope, and the mechanical properties of the membrane were tested by tensile testing. The maximum tensile stress was obtained at 0.746 MPa, and the minimum tensile stress was obtained at 0.487 MPa. Microscopic examination of the membrane’s surface identified the shape, the structure of the fibers formed, and the amount of agglomeration. The flow rate, membrane flux, and normalized water permeability (NWP) were tested, using the water treatment performance test to measure the membrane’s filtering ability.
NANOCON 2021 Conference Proeedings, 2021
Electrospun nanofiber membranes for filtration and medical applications are still under rapid development. The common example of membranes-polyamide 6 (PA6) with hydrophilic properties was selected for the conversion to hydrophobic membranes. The fiber diameter in the membrane is about 100 nm. To reach the hydrophobic properties, the hydrophilic PA6 membrane was plasma coated by CF film from Argon/C 4 F 8 = 2:1 gas mixture in radio frequency (RF) 20 W plasma in total pressure about 0.7 Pa for 5 min. The membranes are by this process coated deeply inside the structure up to underlying spunbond substrate used for the membrane production as a collector substrate. The contact angle measured on CF functionalized membrane is about 120 • and it is higher than the contact angle measured on the reference flat CF coating on Si sample with same chemical bonding. Chemical structure was studied by XPS where identical CFx components were identified on flat samples and on the top of functionalized membrane. The zeta potential decreased significantly if PA6 membrane is functionalized by CF groups. The coating process did not damage the nanofibers in the membrane and the diameters of the fibers were not significantly increased.
Novel modified PVDF ultrafiltration flat-sheet membranes
Journal of Membrane Science, 2012
Polyvinylidene fluoride (PVDF) ultrafiltration membranes were modified using a new type of hydrophilic polyurethane additive, called L2MM. During phase inversion L2MM migrates to the membrane surface and functions as both a pore former and surface modifier. L2MM improved the surface hydrophilicity and significantly increased the PVDF membrane's pure water permeation (PWP) rate. PVDF membranes were modified with two L2MMs: L2MM(PEG-600) and L2MM(PEG-200). PWP tests, contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to assess the impact of L2MM type, L2MM concentration and PVDF concentration on the performance and characteristics of modified PVDF membranes. XPS analysis and contact angle measurements indicated that the L2MM migrated to the membrane surface and the contact angle decreased by up to 19%. SEM and AFM images were used to investigate the relation between surface morphology and ultimate performance. The L2MMs had a significant effect on flux; increasing the L2MM concentration improved membrane PWP fluxes up to a maximum with further increases resulting in flux decreases. Both L2MM(PEG-200) and L2MM(PEG-600) increased the final PWP flux of modified PVDF membranes up to 6.5 times that of the control membranes. Furthermore, L2MM(PEG-200) increased the 100 kDa polyethylene oxide (PEO) separation from 88 to 96% compared to the control membrane.
Desalination, 2014
In this paper, the effects of high molecular weight additive (PEO-PPO-PEO), low molecular weight additive (oxalic acid) and inorganic additive (nano-TiO 2) on PVDF membranes were studied by phase inversion method. The experimental results showed that the contact angle decreased as PEO-PPO-PEO was added in the casting solution. With the increasing concentration of PEO-PPO-PEO from 0.5 to 3.0 wt.%, the water flux increased from 0 to 1136 L/m 2 h and the rejection decreased from 99.0% to 64.0%, meanwhile, the static contact angle stabilized basically around 66°. When the oxalic acid concentration increased from 0 to 3.0 wt.% and the concentration of PEO-PPO-PEO maintained at 0.5 wt.%, the water flux increased from 0 to 192 L/m 2 h, while the rejection firstly decreased and then stabilized around 88.0%.
Ionics, 2012
Poly(vinylidene fluoride-co-hexafluoropropene)hexafluoropropylene (PVdF-HFP; M n , 130,000)-based membranes were prepared by means of phase inversion technique by coagulating with water and MeOH and then doping with H 3 PO 4 and H 2 SO 4. In order to improve the electrochemical properties of the PVdF-HFP membranes, coagulated membranes were also coated with polystyreneblock-poly(ethylene-ran-butylene)-block-polystyrene (PSEBS) and sulfonated with chlorosulfonic acid in the second stage. The effects of the type of coagulant, coagulation time, doping agents, coating, and sulfonation on the membrane properties were investigated. Membranes were thermally stable up to 400°C. The conductivity values were measured to be between 1.10E−01 and 6.00E−03 mS/cm for uncoated samples. The proton conductivity value of the PSEBS-coated and sulfonated membrane was increased from 6.00E−03 to 92.1 mS/cm. Water uptake values varied from 0 to 38 % for uncoated samples and from 11.5 to 65.2 % for coated samples. Chemical degradation of PVdF-HFP membranes was investigated via Fenton test. All membranes were found to be chemically stable. Morphology of the membranes was examined by scanning electron microscopy. Different membrane morphologies were observed, depending on different membrane preparation procedures.