Unmodified Polyvinylidene Fluoride Research Articles

Modification of Polyvinylidene Fluoride (PVDF) Membrane by Polymer Blending with Phase Inversion Method

One of the simplest approaches to improve membrane performance is to increase the hydrophilicity of the membrane. This article describes the manufacture of activated polyvinylidene fluoride (PVDF) based membranes using PVP and chitosan as organic additives, with the specific aim of increasing the hydrophilicity of the membranes. Variations of dope solution were made by adding 1% by weight of PVP and 1, 2, and 3% by weight of chitosan into three different PVDF polymer solutions. The effect of additives on the membrane was obtained by evaluating chemical functional groups by ATR-FTIR, morphological changes by SEM, and filtration performance. SEM images show that the presence of additives changes the morphological structure of the membrane. This change also had a significant impact on the membrane performance, as evidenced by the increased permeability of the pure water solution and the removal of dissolved humic acid. Overall, modified PVDF membranes with 1% by weight of PVP and 1, 2, and 3% by weight of chitosan resulted in much better permeability than unmodified PVDF membranes due to their excellent hydrophilicity.

Facile modification of polyvinylidene fluoride membrane for enhancing dialysis performance: sulfonation, adding polyethylene glycol and tuning coagulation bath temperature

Modifications were successfully carried out on the polyvinylidene fluoride (PVDF) flat sheet membrane, involving the sulfonation and adding polyethylene glycol (PEG), along with variations in the coagulation bath temperature (CBT). The primary objective of these modifications was to examine their impact on the physicochemical characteristics of the membrane and its permeability to a creatinine solution. The findings revealed that the sulfonated PVDF/PEG membrane, printed at a temperature of 30 °C, displayed substantial increases in porosity, hydrophilicity, water uptake and swelling degree. It is important to note that modifications to the PVDF membrane led to a reduction in thermal stability and an increase in creatinine transport efficiency. For the unmodified PVDF membranes, the clearance values for creatinine in phosphate buffer and phosphate buffer saline media were 0.43 (Transport = 28.65%) and 0.42 mg/dL (Transport = 28.05%), respectively. Conversely, the highest creatinine clearance values were achieved by the SPP30 membrane (sulfonated PVDF/PEG-CBT 30 °C), measuring 0.64 mg/dL (Transport = 42.81%) for creatinine and 0.60 mg/dL for urea (Transport = 39.66%). These results indicate that the sulfonated PVDF/PEG membrane exhibits strong potential for use in hemodialysis applications.

Outstanding Separation Performance of Oil-in-Water Emulsions with TiO2/CNT Nanocomposite-Modified PVDF Membranes

Membrane filtration is an effective technique for separating micro- and nano-sized oil droplets from harmful oil-contaminated waters produced by numerous industrial activities. However, significant flux reduction discourages the extensive application of this technology; therefore, developing antifouling membranes is necessary. For this purpose, various titanium dioxide/carbon nanotube (TiO2/CNT) nanocomposites (containing 1, 2, and 5 wt.% multi-walled CNTs) were used for the modification of polyvinylidene fluoride (PVDF) ultrafilter (250 kDa) membrane surfaces. The effects of surface modifications were compared in relation to the flux, the filtration resistance, the flux recovery ratio, and the purification efficiency. TiO2/CNT2% composite modification reduced both irreversible and total filtration resistances the most during the filtration of 100 ppm oil emulsions. The fluxes were approximately 4-7 times higher compared to the unmodified PVDF membrane, depending on the used transmembrane pressure (510, 900, and 1340 L/m2h fluxes were measured at 0.1, 0.2, and 0.3 MPa pressures, respectively). Moreover, the flux recovery ratio (up to 68%) and the purification efficiency (95.1-99.8%) were also significantly higher because of the surface modification, and the beneficial effects were more dominant at higher transmembrane pressures. TiO2/CNT2% nanocomposites are promising to be applied to modify membranes used for oil-water separation and achieve outstanding flux, cleanability, and purification efficiency.

Modifikasi membran polyvinylidene fluoride (PVDF) dengan penambahan polyvinyl pyrrolidone (PVP) dan kitosan dengan metode inversi fasa

One of the simplest approaches to improve membrane performance is to increase the hydrophilicity of the membrane. This article describes the manufacture of activated polyvinylidene fluoride (PVDF) based membranes using PVP and chitosan as organic additives, with the specific aim of increasing the hydrophilicity of the membranes. Variations of dope solution were made by adding 1% by weight of PVP and 1, 2, and 3% by weight of chitosan into three different PVDF polymer solutions. The effect of additives on the membrane was obtained by evaluating chemical functional groups by ATR-FTIR, morphological changes by SEM, and filtration performance. SEM images show that the presence of additives changes the morphological structure of the membrane. This change also had a significant impact on the membrane performance, as evidenced by the increased permeability of the pure water solution and the removal of dissolved humic acid. Overall, modified PVDF membranes with 1% by weight of PVP and 1, 2, and 3% by weight of chitosan resulted in much better permeability than unmodified PVDF membranes due to their excellent hydrophilicity.

Multi-Layered Branched Surface Fluorination on PVDF Membrane for Anti-Scaling Membrane Distillation.

Membrane distillation (MD) has emerged as a promising technology for hypersaline wastewater treatment. However, membrane scaling is still a critical issue for common hydrophobic MD membranes. Herein, we report a multi-layered surface modification strategy on the commercial polyvinylidene fluoride (PVDF) membrane via plasma treatment and surface fluorination cycles. The repeated plasma treatment process generates more reaction sites for the fluorination reaction, leading to higher fluorination density and more branched structures. MD tests with CaSO4 as the scaling agent show that the modification strategy mentioned above improves the membrane scaling resistance. Notably, the PVDF membrane treated with three cycles of plasma and fluorination treatments exhibits the best anti-scaling performance while maintaining almost the same membrane flux as the unmodified PVDF membrane. This study suggests that a highly branched surface molecular structure with low surface energy benefits the MD process in both membrane flux and scaling resistance. Besides, our research demonstrates a universal and facile approach for membrane treatment to improve membrane scaling resistance.

Surface Modification of PVDF Membrane Using Formic Acid for Enhance the Hydrophobicity for Desalination

Membrane distillation (MD) is a thermally driven membrane separation process. In recent years, MD is considered as a key technology for desalination applications. It has been proven that it has numerous advantages compared to other desalination processes such as reverse osmosis. The thermal driving force, no osmotic pressure effect on membrane fluxes are among the advantages of this MD process. Membranes fabricated from hydrophobic polymers such as polyvinylidene fluoride (PVDF) can be a great choice for MD for the desalination process. However, MD membranes are still held back by some problems, most notably due to pore wetting effects, thereby limiting their use in treating seawater for desalination propose. This study proposes the use of carboxylic acid to modify the PVDF membrane to increase its hydrophobicity as a solution to avoid wetting in MD for water desalination. As a first step, membrane produced using PVDF pellets under the phase inversion method. Then the membrane underwent modification using 5wt%, 10wt% and 15wt% of formic acid via immersion technique. The characteristics of membrane produced observed by the contact angle, Fourier-transform infrared spectroscopy (FTIR) and membrane performance test. The impact of the concentration of formic acid solution and feed temperature on the membrane was evaluated. The result showed that by modifying the membrane with formic acid resulted in the increase in contact angle from unmodified PVDF membrane, 83.03° to 100.88° when the membrane modified with formic acid with concentration was 10 wt%. It was subsequently shown through FTIR peaks that formic acid successfully modified the PVDF membranes. Highest salt rejection percentage was also obtained with 68.9% when the feed temperature is 60 °C.

Enhancing the triboelectricity of stretchable electrospun piezoelectric polyvinylidene fluoride/boron nitride nanosheets composite nanofibers

Wearable electronic devices to be worn directly on the body or integrated in clothes need to be flexible, stretchable, biocompatible, and ideally self-powered. Electrospun polyvinylidene fluoride (PVDF)/boron nitride nanosheets (BNNSs) composite nanofibers are prepared and show piezo-triboelectric response under impact and tensile loading. Without further poling, adding 2 wt% of functionalized BNNSs to PVDF yields 500% enhancement in triboelectricity compared to the un-modified PVDF nanofibers. Analyses indicate that at 1.5 wt% and 2 wt% of BNNS concentration, 96% of the output voltage under impact of the piezo-triboelectric nanogenerator originates from the triboelectric contribution. The BNNSs have been shown to increase the charge trapping capability of the composite nanofiber layer and the surface roughness that relates to the significantly increased triboelectric output. The stretchable, durable piezo-triboelectric nanogenerator has potential as self-powered wearable sensors for human motion detection.

Improved antifouling and self-cleaning ability of PVDF ultrafiltration membrane grafted with polymer brushes for oily water treatment

This study focuses on the modification of commercial polyvinylidene fluoride (PVDF) membranes using surface-initiated atom transfer radical polymerization (SI-ATRP) method. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted from PVDF surface and then PEGMA was grafted onto the PVDF-g-PNIPAAm membrane. The aim of the research was to prepare membranes that simultaneously have antifouling and self-cleaning properties. PNIPAAm (lower block) was grafted to give the membrane temperature sensitive property and PPEGMA (upper block) was used to improve hydrophilicity. Morphology, topography and chemical composition of the modified membranes were completely characterized. Antifouling and cleaning ability of modified membranes were investigated using synthetic oily water. Moreover, the role of PEGMA polymerization time on the membrane performance was examined. PNIPAAm-b-PPEGMA modified membrane achieved 64% decrease in fouling ratio compared to unmodified PVDF membrane at best condition. The flux recovery was 99.1% for modified membrane at this condition. Furthermore, the unmodified PVDF membrane showed 91.1% oil rejection; while the modified membrane could reject 98.2% oil molecules. The final flux of all modified membranes were higher than unmodified membrane. These results indicated that PNIPAAm-b-PPEGMA modified membranes have excellent fouling resistance and self-cleaning ability.

Preparation of a hydrophilic and antibacterial dual function ultrafiltration membrane with quaternized graphene oxide as a modifier

In order to improve the anti-biofouling performance of ultrafiltration membrane, quaternized graphene oxide (QGO) was synthesized as a membrane modifier by in-situ growth of quaternary ammonium salt on the graphene oxide surface. A hydrophilic and antibacterial dual functional membrane was prepared with this kind of modifiers by immersion phase inversion method. The modified membrane obviously exhibits enhanced hydrophilicity, antibacterial and mechanical properties than the unmodified Polyvinylidene fluoride (PVDF) membranes. At the same time, it is proved that graphene oxide, as a carrier of quaternary ammonium salt, can significantly reduce the loss of antibacterial substances from the membranes.

Ferrous sulfide and carboxyl-functionalized ferroferric oxide incorporated PVDF-based nanocomposite membranes for simultaneous removal of highly toxic heavy-metal ions from industrial ground water

The deterioration of the aquatic environment by the heavy metal ions contamination causes serious threat to environment and human beings. However, the treatment of complex industrial wastewater by simultaneous removal of multiple heavy metal ions via a one-step method is still extremely challenging. To this end, we synthesize ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide (CFFO) nanoparticles, which were introduced into polyvinylidene fluoride (PVDF) matrix (individually/mixed together in an optimum ratio) through phase inversion technique. Three types of mixed matrix membranes (MMMs) were developed, viz. FeS/PVDF, CFFO/PVDF and FeS/CFFO/PVDF. The prepared membranes were characterized by SEM, TEM, AFM, FTIR, XRD, BET, and XPS techniques. The properties of the membranes were also examined for pure water flux, hydrophilicity, water uptake capacity, mechanical and thermal property, salt separation and simultaneous separation of toxic heavy metal ions such as lead, (Pb), cadmium (Cd), and chromium (Cr) from industrial ground water. The resultant membranes exhibited relatively high water flux (340–1266 L/m2h) than the unmodified PVDF membrane, due to changes in the porosity and hydrophilicity of the membranes. FeS/CFFO/PVDF membrane showed that it could effectively treat Pb, Cd, Cr and As contaminated industrial ground water, simultaneously with a high removal efficiency of about 88% for Cr(VI), 99% for Cd2+, 99% for Pb2+ and 95% for As in a single filtration process. In addition, the developed membranes conspicuously reduce their concentrations below the maximum contaminant level of WHO and BIS (India). The probable mechanism of separation of heavy metal ions through MMMs could be understood through FTIR and XPS techniques. The results of this study inferred that FeS/CFFO/PVDF membrane is a potential candidate for the simultaneous separation of Pb, Cd, Cr, and As.

High-flux PVDF mixed matrix membranes embedded with size-controlled ZIF-8 nanoparticles

The zeolitic imidazolate framework-8 (ZIF-8) nanoparticles were synthesized at two different sizes of 80–100 nm (ZIF-8 (Z1)) and 60–70 nm (ZIF-8 (Z2)) and characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) analyses. The synthesized ZIF-8 nanoparticles were used for modification of polyvinylidene fluoride (PVDF) ultrafiltration membranes prepared by the phase inversion technique. The SEM and atomic force microscopy (AFM) analyses were used to monitor the changes in the morphology and surface properties of the bare and ZIF-8 modified membranes. The results of AFM analysis revealed the decrease in the surface smoothness of the modified membranes. The ZIF-8/PVDF mixed matrix membranes presented higher water flux than the bare PVDF membranes owing to their higher porosity and suitable pore size of the ZIF-8 nanoparticles. By addition of 0.1 wt% of ZIF-8 (Z1) and 0.2 wt% ZIF-8 (Z2) nanoparticles, the modified membranes displayed water flux of 310 and 275 L/m2h, respectively, with 98 and 76% increase compared with the unmodified PVDF membrane. The results indicated that the membranes modified with larger ZIF-8 particles (80–100 nm) showed higher permeability and flux recovery ratio (FRR %) than those with smaller particles (60–70 nm).

Mechanically stretchable piezoelectric polyvinylidene fluoride (PVDF)/Boron nitride nanosheets (BNNSs) polymer nanocomposites

Mechanically stretchable piezoelectric materials are required by wearable devices, such as self-powering sensors and energy harvesters that can monitor human movement and vital biosignals. Polyvinylidene fluoride (PVDF) is a common choice for making flexible piezoelectric sensors but has limited stretchability (strain to failure). Herein we present a new method of significantly increasing the strain-to-failure of PVDF nanofibre membranes by incorporating amino-functionalised boron nitride nanosheets (BNNSs). The PVDF-BNNS nanocomposites were prepared by firstly dispersing a small amount of BNNSs, less than 1.5 wt%, into a PVDF solution and electrospinning. Compared to the un-modified PVDF, the addition of BNNSs yielded increases of eleven times, twice, and forty times in strength, stretchability, and in-plane thermal conductivity, while piezoelectric performance remains unaffected. The higher thermal conductivity offers significantly better heat dissipation ability of piezoelectric sensors than the un-modified PVDF material.

Synthesis, characterization and filtration performance of the polyvinylidene fluoride membrane modified by poly(methyl ethacrylate-co-2-acrylamido-2-methylpropane sulfonic acid)

Abstract To enhance the anti-fouling and separating properties of polyvinylidene fluoride (PVDF) membranes, an amphiphilic copolymer of methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid, poly(MMA-co-AMPS), was designed and synthesized. Through a phase-inversion process, the poly(MMA-co-AMPS) were fully dispersed in the PVDF membrane. The properties of membrane including the surface and cross-section morphology, surface wettability and fouling resistance under different pH solutions were investigated. Compared to the unmodified PVDF membranes, the contact angles of modified PVDF membranes decreased from 80.6° to 71.6°, and the pure water flux increased from 54 to 71 L·m−2·h−1. In addition, the hybrid PVDF membrane containing 0.5 wt% copolymers demonstrated an larger permeability, better fouling resistance and higher recovery ratio via pure water backlashing, when it was compared with the other blend membranes, and the virgin one in the cyclic test of anti-fouling. The modified membranes with the copolymers possessed an outstanding performance and may be used for further water treatment applications.

Experimental and theoretical investigation of thin ZIF-8/chitosan coated layer on air gap membrane distillation performance of PVDF membrane

Despite the conventional desalination methods, membrane distillation (MD) with moderate temperature need, low operating pressure, and high salt rejection is a noteworthy choice for seawater desalination. In this study, a novel thin film composite (TFC) membrane with ultrathin zeolitic imidazolate framework (ZIF-8)/chitosan layer coated on the polyvinylidene fluoride (PVDF) membrane surface was synthesized to improve the membrane distillation (MD) performance for water desalination. Water contact angle analysis did not show significant change in hydrophilicity of TFC and unmodified PVDF membranes while the liquid entry pressure of water (LEPw) for TFC membrane increased significantly due to formation of ZIF-8/chitosan layer on the PVDF membrane surface. As a result of air gap membrane distillation (AGMD) tests, the permeate water flux increased about 350% after formation of ultrathin ZIF-8/chitosan layer on PVDF membrane surface compared to the unmodified PVDF membrane under filtration of saline water (3.5 wt% NaCl). Surprisingly, ZIF-8/chitosan modified membrane showed higher NaCl rejection of >99.5. The antifouling properties of the membranes were also investigated. The TFC membrane presented better antifouling property when real seawater was used as feed solution by flux reduction of 16% and flux recovery of 90% compared with flux reduction of 41% and flux recovery of 67% for the neat PVDF membrane. Moreover, the stability of TFC was investigated by molecular dynamic simulation. Interaction energy computation and diffusion coefficient calculation confirmed good compatibility of ZIF-8 network with chitosan chain and good performance of the TFC membrane in case of water vapor flux.

Determination of progress in acrylic acid modification on polyvinylidene fluoride membrane by infrared spectroscopy

Filtration performances of membranes could be improved by blending with organic/inorganic additives or by treating plasma and radiation induced grafting techniques. In this study, acrylic acid (AA) was applied to surface of the polyvinylidene fluoride (PVDF) membrane by chemical grafting method to obtain better membrane materials. Changes were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and contact angle measurement techniques. The presence of the bands indicated acrylic groups and increase at cross section thickness of AA grafted sample after modification confirmed the progress of grafting. Coated skin layer onto membrane surface was seen at the SEM images. Water uptake capacities (WU%) of acrylic acid grafted membrane increased to 64% from 57% of unmodified PVDF relatively with increasing hydrophilicity understood by decreasing contact angles of AA modified samples. By using easy and low cost method, acrylic acid was effectively incorporated on to surface of the PVDF membrane. That is the convenient application to prepare functional structures which contain specific groups on surface of membrane via acrylic molecules in addition to obtain high performance filtration membranes.

Surface modification of PVDF membrane by radiation-induced graft polymerization for novel membrane bioreactor

Abstract PVDF (poly vinylidene fluoride) membrane was modified with glycidyl methacrylate (GMA) and sodium sulfite using a radiation-induced graft polymerization technique for unique ammonia removal process. Ion exchange capacities (IECs) of unmodified PVDF membrane, modified PVDF membrane and commercial cation exchange membrane (CEM) were investigated. The IEC value increased as the concentration of GMA increased. Batch experiments were carried out to evaluate the ion transport via the modified membrane. The mass flux of ammonia via the CEM and modified membrane at the initial ammonia concentration of 2000 mg/L were 1.16 mg-NH4+/m2 s and 2.89 mg-NH4+/m2 s, respectively.

A method to modify PVDF microfiltration membrane via ATRP with low-temperature plasma pretreatment

The hydrophilic modification of a polyvinylidene fluoride (PVDF) microfiltration membrane via pretreatment with argon plasma and direct surface-initiated atom transfer radical polymerization (ATRP) was studied. Both modified and unmodified PVDF membranes were characterized by Fourier transform infrared spectroscopy (FTIR), water contact angle, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and pore size distribution measurements. FTIR and XPS spectra confirmed that sulfobetaine methacrylate (SBMA) had been grafted onto the membrane surface. The initial contact angle decreased from 87.0° to 29.8° and a water drop penetrated into the modified membrane completely in 8s. The pore size distribution of the modified membrane exhibited a smaller mean value than that of the original membrane. The antifouling properties of the modified PVDF membrane were evaluated by a filtration test using bovine serum albumin (BSA) solution. The results showed that the initial flux of the modified membrane increased from 2140.1L/m2 h to 2812.7L/m2 h and the equilibrium flux of BSA solution increased from 31L/m2 h to 53L/m2 h.

Effects of Plasma-Modified Polyvinylidenefluoride and Polyethersulfone Ultrafiltration (UF) Membrane Treatments on Quality of Soybean Oil

The effects of unmodified and surface-modified polyvinylidenefluoride (PVDF) and polyethersulfone (PES) ultrafiltration membranes on quality of crude soybean oil and crude oil miscellas were studied. Membranes were modified with hexamethyldisiloxane in radiofrequency plasma polymerization (PlzP) at 60 W (PVDF) or 75 W (PES) glow discharge power for 5 min. Contact angle results indicated an interfacial free energy increase between water and solid surface by 2.1- and 12.7-fold for PVDF and PES, respectively, after PlzP, i.e., both membranes became more hydrophobic. Modified PVDF removed 10% more free fatty acids, 8–11% peroxides, and maintained 2–5% more tocopherols compared to those of unmodified PVDF and modified PES. Oxidation products and color compound removal of modified PVDF from crude oil and miscellas were similar to the commercial bleaching step and better than degumming-neutralization step. Total tocopherol loss during modified PVDF treatment was 5.3% and 5.0–6.8% for crude oil and miscellas, respectively, and these values were far below than any processing steps in commercial refining (10.4–28.4% loss). Practical Applications PlzP coating of monomers on a polymeric-based membrane changes the membrane's chemical and physical properties due to series of sequential reactions such as oxidation, degradation and cross-linking. The predominant reactions were determined mainly with plasma power and plasma treatment time. Thus, if one can adjust the plasma parameters properly, one can create a tailor-made surface in terms of angstroms at the molecular/atomic level. The minimal refining method with plasma-modified PVDF and PES membranes described in the present study was a new practical approach to remove undesirable components from crude soybean oil as well as crude oil-hexane miscellas for meeting commercial refining standards. It simultaneously preserves the more healthy minor components found in oil.

PVDF membrane biofunctionalization by chemical grafting

The objective of the work was to develop a suitable method for covalent immobilization of labile active biomolecules on inert hydrophobic polyvinylidene fluoride (PVDF) membrane, preserving both membrane stability and biomolecule activity. PVDF is advantageous over other membrane materials due to its high mechanical strength and excellent chemical resistance. On the other hand, its native structure does not have sites for biomolecules covalent immobilization in mild conditions. The strategy of the present work consisted in grafting reactive groups on the hydrophobic PVDF to which attaching functional groups able to covalently bound biomolecules in mild conditions. Tuning grafting conditions were crucial in order to attack the inert membrane while maintaining suitable membrane chemical and mechanical stability. Therefore, surface modification of native PVDF flat-sheet membranes was performed by wet chemical strategy, under basic conditions, using 1,5-diamino-2-methylpentane (DAMP) as carrier of amino groups. Afterwards, these groups were activated with glutaraldehyde (GA) to which biomolecules were easily attached by covalent bond. Two model proteins having different properties (BSA and Lipase) were selected for immobilization test. DAMP concentration, reaction temperature, and reaction time were studied in order to tune both the degree of modification and the loading capacity of the functionalized membrane taking in account the mechanical stability of the membrane. Modified and native PVDF membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), the ninhydrin test, scanning electron microscopy (SEM) and the mechanical resistance test. Enzymatic activity of immobilized lipase was tested in a biphasic systems using the hydrolysis of triglycerides as model reaction.Modified membranes showed higher binding capacities compared with unmodified PVDF membrane. Optimal conditions for grafting reactive amino groups able to guarantee membrane stability and enzyme loading suitable to achieve good enzyme specific activity were identified.

Development of a Novel Affinity Membrane Purification System for Deoxyribonuclease

A membrane based affinity purification system was developed for the purification of the DNA specific nuclease, DNase I. Single stranded DNA was bound to unmodified polyvinylidene fluoride (PVDF) membranes which were used to purify DNase I from a solution of bovine serum albumin. Using coated membranes, a 6-fold increase in specific activity was achieved with 80 % enzyme recovery. This method provides a simple yet effective way to purify DNase I and can be very useful for the purification of other DNA specific enzymes.