Electrospun fiber membranes from blends of poly(vinylidene fluoride) with fouling‐resistant zwitterionic copolymers

Nonwoven super‐hydrophobic fiber membranes have potential applications in oil–water separation and membrane distillation, but fouling negatively impacts both applications. Membranes were prepared from blends comprising poly(vinylidene fluoride) (PVDF) and random zwitterionic copolymers of poly(methyl methacrylate) (PMMA) with sulfobetaine methacrylate (SBMA) or with sulfobetaine‐2‐vinylpyridine (SB2VP). PVDF imparts mechanical strength to the membrane, while the copolymers enhance fouling resistance. Blend composition was varied by controlling the PVDF‐to‐copolymer ratio. Nonwoven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers in a mixed solvent of N,N‐dimethylacetamide and acetone. The PVDF crystal phases and crystallinities of the blends were studied using wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). PVDF crystallized preferentially into its polar β‐phase, though its degree of crystallinity was reduced with increased addition of the random copolymers. Thermogravimetry (TG) showed that the degradation temperatures varied systematically with blend composition. PVDF blends with either copolymer showed significant increase of fouling resistance. Membranes prepared from blends containing 10% P(MMA‐ran‐SB2VP) had the highest fouling resistance, with a fivefold decrease in protein adsorption on the surface, compared to homopolymer PVDF. They also exhibited higher pure water flux, and better oil removal in oil–water separation experiments. © 2018 Society of Chemical Industry     

Lead-free NaNbO3-based ferroelectric perovskites and their polar polymer-ceramic composites: Fundamentals and potentials for electronic and biomedical applications

Ferroelectric lead-free NaNbO₃-based ceramics are the most promising candidates to a wide range of advanced technological applications as sensors, transducers and actuators. In special, (K,Na)NbO₃ (KNN) and (Ba,Na)(Ti,Nb)O₃ (BTNN) show interesting structural properties, including morphotropic phase boundaries regions that lead to exceptional dielectric, piezoelectric and ferroelectric responses. Also, the biocompatibility of these compounds allows their application as biomedical sensors, medical devices, and bone tissue replacement. In this way, high impact applications can be achieved with ferroelectric lead free NaNbO₃ – based (NN-based) ceramics. In this review, we will explore the strategies for the improvement of ferroelectric, dielectric and structural properties reviewing the effects of the synthesis process, microstructure and chemical composition of lead-free complex perovskite ceramics, specially KNN and BTNN, as well as, PVDF-KNN and PVDF-BTNN polymer-ceramic and the (PVDF-TrFE)-KNN copolymer-ceramic composites to provide new insights and research opportunities for the development and improvement of fundamental properties of such systems considering their potential for technological applications, especially for the biological ones.     

Research on hydrophobicity of electrospun Fe3O4/PVDF nanofiber membranes under different preparation conditions

Abstract

Preparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe₃O₄/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe₃O₄ nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe₃O₄ nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe₃O₄/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes has been enhanced.     

Poly(vinylidene fluoride) (PVDF) membranes for fluid separation

The importance of poly(vinylidene fluoride) (PVDF) as a membrane material has long been recognised in many membrane processes. Compared to other types of polymeric membranes, the PVDF membranes have received great attention because of its outstanding properties including high hydrophobicity, thermal stability, chemical resistance and excellent mechanical strength. This article provides an overview of recent development in PVDF membrane processes, focussing on the commercial PVDF membrane products for water and wastewater treatment and possible applications of PVDF membranes in areas such as membrane based gas absorption and membrane distillation where no substantial commercial PVDF membrane processes are available so far.     

Thermally stable cellular poly(vinylidene) ferroelectrets: Optimization of CO2 driven inflation process

Electrically charged cellular ferroelectrets can show excellent thermally stable piezoelectric activity and are therefore progressively used in electrochemical transducers. Given that an optimized cellular structure is a key for improving charge density and the associated piezoelectric properties in this material, we investigated the influence of CO₂ inflation treatment using various gas diffusion expansion or inflation procedures on the piezoelectric d₃₃ coefficient and thermal stability of cellular poly(vinylidene) ferroelectrets and compare with the results (partially) obtained by N₂ inflation as reported in our previous study (Jahan, Mighri, Rodrigue, Ajji, J. Appl. Polym. Sci. 2019, 136, 47540). Samples were prepared using the conventional extrusion–stretching–inflation–corona charging method. Maximum d₃₃ coefficient for CO₂-inflated samples is found to be around 30% higher than that of N₂-inflated samples (327 pC/N compared to 251 pC/N) by stepwise pressure application method. The key parameters addressed in the inflation procedures are the changes in sample thickness, morphology, and the void-height distribution in both gas treatments. The ferroelectrets show excellent thermal stability for up to 4 days at 90, 110, and 120 °C in both treatments with a slightly improved performance in CO₂ gas. The higher activation energy of CO₂-inflated samples (0.52 eV) than the N₂-inflated ones (0.43 eV) further confirms the stability data. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47929.     

Achieving β-phase poly(vinylidene fluoride) from melt cooling: Effect of surface functionalized carbon nanotubes

Poly(vinylidene fluoride) (PVDF) based nanocomposites with different surface-functionalized multi-walled carbon nanotubes (MWCNTs) were prepared by melt mixing in a small scale compounder. With the incorporation of commercial functionalized MWCNTs, the β-phase in PVDF can be directly achieved from melt cooling, as verified by results of Fourier transform infrared spectrum and X-ray diffraction. Interestingly, nanocomposites with amino group functionalized MWCNTs showed the highest percentage of β-phase (17.4%) formation in PVDF, followed by those with hydroxyl groups (11.6%) and unmodified MWCNTs (9.4%). However, the nanocomposites containing MWCNTs with carboxyl groups which were thought to be able to well interact with the dipoles on PVDF chains have the lowest amount of β-phase, i.e. 4.7%. The analysis on the mechanism of the influence of surface functionalization of MWCNTs on the formation of β-phase in PVDF shows that the combined effects of the dispersion of MWCNTs and the nanotube–polymer interactions account for the formation of the β-phase in PVDF.     

Electroactive phases of poly(vinylidene fluoride): Determination,processing and applications

Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.     

Atom transfer radical polymerization (ATRP): A versatile and forceful tool for functional membranes

The progress in atom transfer radical polymerization (ATRP) provides an effective means for the design and preparation of functional membranes. Polymeric membranes with different macromolecular architectures applied in fuel cells, including block and graft copolymers are conveniently prepared via ATRP. Moreover, ATRP has also been widely used to introduce functionality onto the membrane surface to enhance its use in specific applications, such as antifouling, stimuli-responsive, adsorption function and pervaporation. In this review, the recent design and synthesis of advanced functional membranes via the ATRP technique are discussed in detail and their especial advantages are highlighted by selected examples extract the principles for preparation or modification of membranes using the ATRP methodology.     

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 4 wt.% of PEG-400. The prepared membranes presented smaller mean pore size (0.13 μm) and significantly higher wetting pressure (550 kPa) compared to the plain membrane. From CO₂ stripping test, at water velocity of 0.4 m/s, the PVDF membranes prepared by 4% PEG-400 demonstrated an approximate CO₂ stripping flux of 4.5 × 10⁻⁵ (mol/m² s) 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.