Poly(vinylidene fluoride)/poly(acrylonitrile) blend fibrous membranes by centrifugal spinning for high‐performance lithium ion battery separators

Fibrous membranes are promising as high‐performance lithium ion battery separators because of high porosity and superior electrolyte uptake. Electrospinning is a popular approach to produce fibrous membranes, but its production rate is very low. As a comparison, mass production of fibrous membranes can be achieved by centrifugal spinning. This study reports fibrous membranes based on poly(vinylidene fluoride)/poly(acrylonitrile) blends by centrifugal spinning and their application as lithium ion battery separators. The blend fibrous membranes have high electrolyte uptake of about 300%, excellent dimensional stability at 180 °C and good mechanical strength over 18 MPa. The coin cells with the blend fibrous membranes as separators show high discharge capacity of 147.7 mAh/g at 0.2 C and superior C‐rate performance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44515.     

Preparation of superhydrophobic nanocomposite fiber membranes by electrospinning poly(vinylidene fluoride)/silane coupling agent modified SiO2 nanoparticles

Superhydrophobic nanocomposite fiber membranes were prepared by blend electrospinning of poly(vinylidene fluoride) (PVDF) mixed with silane coupling agent modified SiO₂ nanoparticles. The nanoparticles were prepared by the sol–gel method, and the average particle diameter was measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The effects of the type of silane coupling agent, such as n‐octyltriethoxysilane, vinyltrimethoxysilane (A‐171), and vinyltriethoxysilane (A‐151), and the mass ratio of the modified silica particles and PVDF on the surface wettability of the composite fiber membrane were investigated. The results indicated that the incorporation of silane coupling agent modified silica particles into the PVDF membrane increased the roughness of the surface and formed micro/nano dual‐scale structure compared to the pristine PVDF membrane, which was responsible for the superhydrophobicity and self‐cleaning property of the nanocomposite fiber membranes. The value of water contact angle (CA) increased with the increase of the content of modified SiO₂ nanoparticles in the nanocomposite membrane, ranging from 149.8° to 160.1° as the mass ratio of modified 170 nm SiO₂ with PVDF matrix increased from 0.5:1 to 5:1, indicating the membrane possesses a superhydrophobic surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44501.     

Evaluation of the antifouling and photocatalytic properties of novel poly(vinylidene fluoride) membranes with a reduced graphene oxide–Bi2WO6 active layer

Immobilization of reduced graphene oxide (RGO)–Bi₂WO₆ is an ideal method for obtaining antifouling membranes for membrane distillation (MD) processes. Poly(vinylidene fluoride) membranes modified with RGO–Bi₂WO₆ were successfully obtained with a double‐layer coating method through non‐solvent‐induced phase separation. The water contact angle was improved by about 30° by RGO–Bi₂WO₆; this indicated that the surface modification obviously increased the membrane hydrophobicity. The high desalination rate proved that all of the prepared membranes were appropriate for the MD process. The RGO–Bi₂WO₆‐modified membranes achieve 26.26%–59.95% removal rates in 10 mg/L aqueous ciprofloxacin under visible light for 7.5 h. It was possible to erase strongly bound foulants and recover the prepared membrane's permeation flux by 3 h of visible‐light irradiation. The RGO–Bi₂WO₆‐modified membrane with a high hydrophobicity, fouling mitigation, and photocatalytic capability presents huge potential for the treatment of high‐salt antibiotic wastewater use in the MD process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45426.     

Characterization of poly(vinylidene fluoride) flat sheet membranes prepared in various ratios of water/ethanol for separator of li‐ion batteries: Morphology and other properties

PVDF, poly(vinylidene fluoride), membranes were prepared and investigated by a scanning electron microscope, a universal testing machine, and capillary porometer for its potential use as a separator in lithium ion batteries. The membranes were prepared by phase inversion with different polymer types, concentrations of solution, amounts of additive, and nonsolvent ratios of water/ethanol. The morphology of membranes is affected by the ratio of both the coagulation bath (water/ethanol) and a low molecular weight additive (polymer/solvent/additive). The results showed that significant variations in the membrane were detected when adding an additive to the casting solution or ethanol to the coagulation bath. With an increased concentration of ethanol, the upper structure was found to be transformed into a sponge‐like arrangement. In the case of Solef®1015 of the same polymer concentration, despite the higher molecular weight of 1015, a relatively small sized nucleus is formed, resulting in a denser network and relatively uniform membrane structure being formed. Mechanical testing showed that the tensile strength of the PVDF membranes increased when added to a 25 wt % ethanol coagulation bath, whereas it is decreased when added to higher concentrations of ethanol in the bath or additives in the casting solution. In a bath condition of water/ethanol = 75/25 wt % (Bath no. 2), the value of tensile strength is 7.11 and 7.52 MPa, for Solef®6010 20 wt % and Solef®1015 17 wt %, respectively. The thickness of the prepared membrane is 21–34 μm and the porosity is up to 50%. The electrolyte absorption changes of the fabricated membranes at different conditions are measured from 151 to 223 ± 15%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Outstanding antifouling performance of poly(vinylidene fluoride) membranes: Novel amphiphilic brushlike copolymer blends and one-step surface zwitterionization

In this study, we endowed a poly(vinylidene fluoride) (PVDF) membrane with outstanding antifouling ability by blending the hierarchical amphiphilic brushlike copolymer [poly(hydroxyethyl methacrylate)-b-polydimethylsiloxane-b-poly(hydroxyethyl methacrylate)]-g-poly(N,N-dimethylamino-2-ethyl methacrylate) with different initial monomer/initiator feed ratios and performing a one-step surface zwitterionization of spontaneously segregated poly(N,N-dimethyl aminoethyl methacrylate) segments. Interestingly, nanoscale granular micelles were formed on the surface during zwitterionization because of the migration and self-assembly of the amphiphilic copolymer; this contributed to the membrane hydrophilicity and antifouling ability. During the filtration of the model foulant bovine serum albumin (BSA) aqueous solution, the BSA rejection ratio and flux recovery ratio increased remarkably to 94.8 and 100.0%, respectively. Moreover, the modified membranes also possessed stable and durable antifouling properties after three cycles of BSA filtration. Thus, this study provided a versatile method for constructing a PVDF ultrafiltration membrane that could achieve high permeability and good antifouling properties in efficient wastewater treatment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47637.     

Improved dispersion of carbon nanotubes in poly(vinylidene fluoride) composites by hybrids with core–shell structure

Core–shell structure hybrids of carbon nanotubes (CNTs)/BaTiO₃ (H‐CNT‐BT) and commercial multi‐wall CNTs are respectively incorporated into poly(vinylidene fluoride) (PVDF) for preparing the composites near the percolation thresholds. A comprehensive investigation for CNT's dispersion and composite's conductivity is conducted between H‐CNT‐BT/PVDF and CNT/PVDF at different depths vertical to the injection's direction. Gradual increases of the conductivity in two composites are observed from the out‐layer to the core part which infers an inhomogeneous CNT's dispersion in the interior of composites due to their migration under flow during the injection. However, the use of H‐CNT‐BT fillers with core–shell structure enables to reduce this inhomogeneous dispersion in the composite. Furthermore, the conductive network of CNTs in H‐CNT‐BT/PVDF is less sensitive to the thermal treatment than the one in CNT/PVDF composite, which infers the core–shell structure of hybrids can ameliorate the sensitivity of the conductive network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45693.     

Morphology and properties of poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through melt mixing. The morphology, rheology, crystallization behavior, mechanical properties, dynamic mechanical properties and thermal properties of the PVDF/SR blends were investigated. The blend with 9 wt % of SR showed spherical shape of disperse phase whereas the blend with 27 wt % of SR resulted in irregular shape of rubber phase. The rheology showed that the complex viscosity and storage modulus of the blends decreased with increasing the SR content. The mechanical properties of the blends were decreased with increasing the SR content but that were significantly improved after dynamical vulcanization. The crystallization temperature of PVDF phase in PVDF/SR blends was increased. The incorporation of SR improved the thermal stability of PVDF/SR blends, and the temperature at 10% mass loss of the blends increased to about 489°C compared with 478°C of the pure PVDF. The mass of residual char in experiment of the blends was lower than that obtained in theory. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39945.     

Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt

The influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF₂) has been investigated. The DSC endotherms of PVF₂ crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.     

Synthesis,characterization, and flocculation performance of anionic polyacrylamide P (AM‐AA‐AMPS)

In this study, a kind of anionic polyacrylamide (P(AM‐AA‐AMPS)) was synthesized using acrylamide (AM), acrylic acid (AA), and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) under ultraviolet (UV) irradiation. The conditions of the polymerization reaction such as monomer mass ratio, solution pH value, EDTA concentration and urea concentration were investigated by using the single factor approach and an L₁₆ (4⁵) orthogonal array. The structure and morphologies of the copolymer were determined by nuclear magnetic resonance spectrometer (NMR), infrared spectrometer (IR) and scanning electron microscope (SEM). The results show P(AM‐AA‐AMPS) with the intrinsic viscosity of 1.5 × 10³ mL g^?1 was synthesized at optimal conditions: mass ratio, m(AM) : m(AA) : m(AMPS) of 70 : 10 : 10, pH value of 9.0, EDTA concentration of 0.10% and urea concentration of 0.20%. In addition, P(AM‐AA‐AMPS) had better flocculation efficiency than commercial PAM in sludge dewatering experiment; the minimum filter cake moisture content could be reduced to 65.1%. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of the coagulation medium on the performance of poly(ether sulfone) flat‐sheet membranes

Poly(ether sulfone) flat‐sheet membranes were fabricated via phase inversion with different nonsolvent mixtures. The effect of the nonsolvent water with the addition of various amounts of ethanol, acetone, or isopropyl alcohol on the membrane morphology (as measured with scanning electron microscopy and atomic force microscopy) and the filtration performance were investigated. For the statistical evaluation of the fabrication process, on average, six membranes were produced. The pure water flux (PWF) and macromolecule retention were determined via filtration experiments. The presence of coagulation additives resulted in modified precipitation kinetics and thermodynamics, yielded different membrane structures, and therefore, influenced the performance. The results show that the addition of ethanol, acetone, and isopropyl alcohol in low concentrations (up to 10%) to water led to an increasing PWF. Higher concentrations led to a decrease in PWF. For high concentrations (>30%), a change in the membrane morphology from fingerlike to spongelike structures was expected, and this was experimentally proven for the case of ethanol. One main finding was the similarity of the influence of the used additives on the membrane performance. This was to be expected from Flory–Huggins theory for additives with high water miscibility; hence, under these circumstances, entropic and not energetic reasoning dominated the phase‐inversion process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41645.     

Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature (T_c) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T_c above 164 °C, but coexisted with α phase at T_c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T_c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T_c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T_c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T_c was in the range of 144–160 °C. As T_c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T_c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T_c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43605.     

Spherulitic Morphology and Crystallization Kinetics of Poly(vinylidene fluoride)/Poly(vinyl acetate) Blends

Spherulitic morphology and crystallization kinetics of the blends of poly(vinylidene fluoride) (PVDF) and poly(vinyl acetate) (PVAc) prepared by solution casting films have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results suggested that PVAc was mainly segregated into the interlamellar and/or interfibrillar regions due to the volume-filling spherulitic morphology observed. As for the results of crystallization kinetics, it was found that both the PVDF spherulitic growth rate (G ^PVDF) and the overall crystallization rate constant (k _n ) were depressed with either the addition of PVAc component or the increase of crystallization temperature (T _c). The kinetics retardation was attributed to the decrease in PVDF molecular mobility and dilution of PVDF concentration due to the addition of PVAc, which has a higher glass transition temperature (T _g).     

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     

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     

In situ grafting onto solution polymerized styrene butadiene rubbers (SSBR) filled with silica via solid state method

Grafting reaction of solution polymerized styrene butadiene rubbers (SSBR) and 3‐mercaptopropionic acid in situ was investigated in a solid state and a series of SSBR with different polarity degree were prepared through grafting 3‐mercaptopropionic acid onto SSBR chains in the process of mixing. The feasibility of solid‐phase grafting in situ (SPGiS) was verified by ¹H‐nuclear magnetic resonance and Fourier transform infrared spectroscopy. Compared with unmodified SSBR/silica compounds, the SSBR/silica compounds with SPGiS exhibited preferable performance in silica dispersion, rubber‐filler interaction, and reinforcing efficiency. The scanning electron microscope and transmission electron microscope showed that silica presented better dispersion and smaller aggregates in the SSBR of SPGiS. Dynamical mechanical analysis of vulcanized rubber compounds with SPGiS showed that the wet skid resistance and the rolling resistance of SSBR/silica compounds were improved separately. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46653.     

Thermodynamic compatibility of sepiolite-filled poly(vinylidene fluoride)-polystyrene blends

Summary Inverse gas chromatography (IGC) and differential scanning calorimetry (DSC) were used to investigate the effect produced by sepiolite on the thermodynamical compatibility of poly(vinylidene fluoride)-polystyrene blends. Polymer-polymer interaction parameters were calculated from the retention data, for various polar and non-polar probes in pure and mixed stationary phases of these polymers, using sepiolite as solid support, as well as from melting point depression analysis of the sepiolite filled blends. Both techniques give us positive values of the interaction parameters, in accordance with the non-compatibility of these blends; However negative values of the interaction parameters were obtained for polystyrene-rich blends (_PS 85 wt%) and high sepiolite loadings, indicating that sepiolite acts as a compatibilizing agent for the system PVF₂/PS.     

Strong effects of Tween 20 additive on the morphology and performance of poly(vinylidene fluoride) hollow‐fiber membranes

Poly(vinylidene fluoride) (PVDF) hollow‐fiber membranes were prepared from a Tween 20/water/triethyl phosphate/PVDF system. The effects of Tween 20 on the morphology and properties of the membranes were explored. Field emission scanning electron microscopy imaging indicated the presence of skinlike layers on both surfaces of the membranes. In the cross section, a bicontinuous morphology comprised of interlocked crystallites was observed. As the dosage of Tween 20 was raised, the size and quantity of nanopores on the surfaces increased, and the morphology of the crystallites in the cross section changed from sheaflike to sticklike. Tween 20 was removed almost completely during the membrane‐formation process, as validated by Fourier transform infrared–attenuated total reflection and ¹H‐NMR spectrometry. Dextran filtrations were preformed to demonstrate the potential applications of these membranes in separation processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44600.     

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.     

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