Improving Properties of Poly(vinylidene fluoride) by Adding Expanded Graphite without Surface Modification via Water‐Assisted Mixing Extrusion

Expanded graphite (EG) is introduced into poly(vinylidene fluoride) (PVDF) by melt mixing extrusion with water injection. The results demonstrate that the unfunctionalized EG in composite prepared with water injection exbibits better dispersion than that in the one prepared without water injection due to the promoting role of water during extrusion. Thus, the PVDF/EG composite with loading of 4 wt% prepared by water‐assisted mixing extrusion (WAME) exhibits electrical conductivity of about three orders of magnitude higher than the neat PVDF and one order of magnitude higher than the one prepared without water injection. Comparing to the neat PVDF, the thermal conductivity of the composites prepared with and without water injection is increased by 101.5% and 75.0%, respectively. The introduced EG leads to increased Young’s modulus and tensile strength especially for the composite prepared by WAME. The present work indicates that WAME can promote the dispersion of EG in PVDF matrix without any extra functionalization.     

Melt rheology and mechanical crystal transformation in an immiscible blend with poly(vinylidene fluoride) matrix

Effect of immiscible polyamide 6 (PA6) on the melt rheology and stretch‐induced crystal transformation of poly (vinylidene fluoride) (PVDF) matrix is reported. PA6 is dispersed as submicron droplets in the PVDF matrix, responsible for significant enhancement in the melt elasticity. Nevertheless, crystallization habits of PVDF matrix from melt are little affected by submicron PA6 droplets, and the α‐form of PVDF prevails in the blends. Upon mechanical stretching, the α‐form is converted to the β‐form, which is remarkably reduced with the increasing of PA6 content in the blends. It could be correlated with the decreased tensile stress in the presence of submicron PA6 droplets that act as stress concentrators. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43499.     

Influence of nano silica hybrid expandable graphite on flammability,thermal stability,and mechanical property of polypropylene/polyamide 6 blends

Silica (SiO₂) nanohybrid expandable graphite (nEG) particles fabricated through one-step method are used as an efficient flame retardant for polypropylene (PP)/polyamide 6 (PA6) blends. The effect of nEG on the flammability, thermal stability, crystallization behaviors, and mechanical properties of PP/PA6 composites is investigated by using limit oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared, scanning electron microscopy, and mechanical tests. Compared with pure expandable graphite (EG), nEG improves the flame retardancy of composites. The results of LOI show that LOI of PP/PA6/nEG10 and PP/PA6/nEG15 composites are 26.0% and 27.2%, respectively. But the LOI values of PP/PA6/EG10 and PP/PA6/EG15 composites are 25.7% and 26.9%, respectively. The UL-94 test results show that PP/PA6/nEG10 composites reach V-1 level when the nEG content is only 10%. However, the PP/PA6 composites with 10% EG does not pass the UL-94 test. In addition, PP/PA6 composites with 15% nEG can reach V-0 level. The CCT results further show that nEG has a higher flame-retardant efficiency than pure EG for PP/PA6 blends. The thermal stability of PP/PA6/nEG composites is better than that of PP/PA6/EG composites. The mechanical property tests indicate that nEG is more conducive to maintain the tensile and impact strengths of PP/PA6 blends than EG due to the enhanced compatibility and interfacial adhesion.     

Piezoelectric properties of noncovalently functionalized 2D nanomaterials incorporated poly(vinylidene fluoride) nanocomposites

We report here for the first time the role of noncovalently functionalized 2D nanomaterials on the ferroelectric and piezoelectric behavior of poly(vinylidene fluoride) (PVDF) nanocomposites. Graphene oxide (GO), expanded graphite (EG) and hexagonal boron nitride (h-BN) were noncovalently modified via Li-salt of 6-amino hexanoic acid (Li-AHA), denoted as m-GO, m-EG and m-BN, in order to de-agglomerate and de-stack them, which were subsequently incorporated into the PVDF matrix via solution mixing, followed by compression molding. Simultaneously, PVDF nanocomposites with unmodified 0.08 wt% of 2D nanomaterials were also prepared using the same methodology. PVDF/m-BN nanocomposite showed a higher extent of polar phase (~36%) associated with PVDF phase as compared to PVDF/m-GO and PVDF/m-EG nanocomposites. Further, the highest permittivity (~58 at 10⁻¹ Hz) was achieved in PVDF/m-BN nanocomposite, which was also reflected in higher remnant polarization (~61 nC/cm²) and a significantly higher d₃₃ value (~53 pm/V). Moreover, a higher output peak to peak voltage (~13 V) was obtained for the sensor device fabricated from PVDF/m-BN nanocomposite. Thus, the role of Li-AHA-modified 2D nanomaterials in improving the morphology, dielectric, ferroelectric, and piezoelectric characteristics of the PVDF nanocomposites was clearly established.     

Dielectric properties of multiwalled carbon nanotube/clay/polyvinylidene fluoride nanocomposites: Effect of clay incorporation

This study investigates the effect of clay addition on the broadband dielectric properties of multi‐walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF) composites, that is, frequency range of 10¹−10⁶ Hz. Different loadings of MWCNT and clay were used for the preparation of three‐phase (MWCNT/Clay/PVDF) nanocomposites via melt‐mixing method. The crystalline structure and morphology of nanocomposites were examined by employing characterization techniques such as X‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The dielectric spectroscopy showed that introducing clay into the MWCNT/PVDF nanocomposites at a critical MWCNT concentration improved dielectric properties tremendously. It was interestingly observed that the incorporation of a specific amount of clay, that is, 1.0 wt%, into the (MWCNT/PVDF) nanocomposite at a critical MWCNT loading, that is, 0.5 wt% MWCNT, resulted in a huge increase in the dielectric permittivity (670% at 100 Hz) and a considerable reduction in the dissipation factor (68% at 100 Hz). POLYM. COMPOS., 161–167, 2016. © 2014 Society of Plastics Engineers     

Improving dielectric properties of poly(vinylidene fluoride) composites: effects of surface functionalization of exfoliated graphene

To investigate the effects of surface functionalization of exfoliated graphene (EG) on the crystalline form of β-phase and dielectric properties of poly(vinylidene fluoride) (PVDF), we prepared PVDF-based composites reinforced by different functionalized EG. The X-ray photoelectron spectroscopy results indicated that a wide variety of chemical functional groups such as C–OH, C–O–C, C=O, COOH and C–F could be introduced on the surface of modified EG. As confirmed by results of Fourier transform infrared spectrum and X-ray diffraction, the β-phase PVDF can be produced in the composites with the incorporation of functionalized EG. In the frequency ranging from 10² to 10⁷ Hz, the dielectric permittivity of PVDF composites shows an obvious increase owing to a variation of the carbonyl group (C=O) content. Among all the composites, the EG grafted with polymethyl methacrylate/PVDF composite has the highest dielectric permittivity and dielectric loss.     

Investigation on carbon nanotube oxide for anhydrous proton exchange membranes application

The widespread participation of polymers in the membrane preparation has been considering to be critical for the development of proton exchange membranes (PEMs). For the polymers without functional groups to conduct protons, the introduction of proton conduction carriers with the formation of composite membranes is an effective strategy to prepare PEMs with the outstanding proton conductivity. However, there remains a potential risk of the components leaking from composite membranes due to the lack of the interaction force. Here, the composite of carbon nanotube oxide (OCNT) assembling with cadmium telluride (CdTe) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) was introduced into the system of phosphoric acid (PA) doping poly(vinylidene fluoride) (PVDF) with the formation of PVDF/OCNT-CdTe-bmimPF₆/85%PA membranes. PA molecules are anchored by the inorganics of OCNT-CdTe-bmimPF₆ and are stabilized in membranes. The high and stable proton conductivity values at the elevated temperature are obtained comparing the reported PVDF/bmimPF₆/PA membranes. Specifically, the proton conductivity value reached 1.28 × 10⁻¹ S/cm at 160 °C and the value is stable 1.70 × 10⁻² S/cm at 120 °C lasting for 350 h. The fine stability in components could make the membranes extricate from the predicament of proton conductivity decline exceeding 120 °C under anhydrous conditions in PVDF/bmimPF₆/PA membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48833.     

Preparation and properties of β‐phase graphene oxide/PVDF composite films

We report preparation of graphene oxide (GO) from expanded graphite (EG) via a modified Hummers method. GO/PVDF composites films were obtained using solvent N, N‐Dimethylformamide (DMF) and cosolvent comprising deionized water/DMF combination. X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that the main crystal structure of the composite films is β‐phase, and use cosolvent method tends to favor the formation of β‐phase. Scanning electron microscopy (SEM) was used to investigate the microstructure of composite films. Storage modulus and loss modulus were measured by Dynamic mechanical analysis (DMA). Broadband dielectric spectrum tests showed an increase in the dielectric constant of the GO/PVDF composite films with the rising content of GO, and by cosolvent method could improve the dielectric constant while reducing the dielectric loss. Our method that uses GO as an additive and deionized water/DMF as the cosolvent provides a promising and low‐cost pathway to obtain high dielectric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41577.     

不同膨胀体积改性膨胀石墨及其填充PA66性能

采用化学氧化法制备了不同膨胀体积的膨胀石墨(EG),通过聚丙烯酸酯对不同膨胀体积的EG进行包覆改性,利用改性后的EG制备改性EG/聚酰胺66(PA66)复合材料,研究了不同膨胀体积的改性EG对复合材料力学性能和导热性能的影响。结果表明,EG经丙烯酸酯改性后,EG的表面粗糙度和活性基团明显增加;复合材料弹性模量和弯曲强度均随改性EG膨胀体积的增加而增加,与未膨胀石墨相比,分别提升了36.1%、25.8%;拉伸强度、断裂伸长率和热导率随膨胀体积的增加呈先增加后减小的趋势。拉伸强度在EG膨胀体积为40 mL/g时达到最大值,为75.6 MPa;热导率在膨胀体积为20 mL/g时最佳,为2.56 W/(m·k),与未膨胀石墨相比,拉伸强度和热导率分别提升了33.3%和30.1%。     

Graphene–polyamide-6 composite for additive manufacture of multifunctional electromagnetic interference shielding components

Graphene–polyamide-6 composite (GC) filament with 9%·v/v graphene concentration was applied as feedstock in filament-based material extrusion (ME) additive manufacturing. The materials are characterized by melt flow index (MFI), mechanical properties, dielectric properties, and electromagnetic interference shielding effectiveness (EMI SE) in the X-band frequency range. Despite high graphene concentration, MFI is unaffected. In ME test specimens; GC has both superior elastic modulus and tensile strength at yield when compared with the neat polymer. Enhanced mechanical properties at high graphene concentration without diminished processability highlight the suitability of polyamide-6 (PA6) as matrix material for graphene composite filaments. Scanning electron microscopy (SEM) imaging indicates graphene alignment in GC after printing. In both compression molded (CM) and ME test specimens, dielectric properties and EMI SE of PA6 are enhanced by graphene inclusion. Further analysis reveals that ME has a negative influence on absorption of electromagnetic waves, while reflection is virtually unaffected.     

聚偏氟乙烯/石墨烯复合材料的制备及性能研究

用溶液共混法制备出聚偏氟乙烯/氧化石墨烯复合材料(PVDF/GO)，经高温热压将GO还原得到聚偏氟乙烯/还原氧化石墨烯复合材料(PVDF/rGO)。研究了填料种类及含量对复合材料电学性能、热稳定性和力学性能的影响。结果表明：随GO和rGO的添加，两种复合材料的介电常数(ε _r)均变大、介电损耗(tanδ)变化不大；低含量下GO和rGO均能提高PVDF的热稳定性，但rGO对PVDF性能的改善效果更好；随填料含量从0增加到8%(质量)，100 Hz下PVDF/rGO复合材料的ε _r从3.60增加到38.30，PVDF/rGO[4%(质量)]复合材料失重率为5%的分解温度较纯PVDF提高了6.44℃。rGO增强了PVDF的刚性，PVDF/rGO复合材料的拉伸强度先增大后减小，杨氏模量逐渐增大，当rGO含量为4%(质量)时拉伸强度最大，拉伸强度和弹性模量分别较纯PVDF提高了35.30%、22.58%。但GO和rGO都降低了复合材料的击穿场强。     

Hydrophobic SiO2 nanoparticle-induced polyvinylidene fluoride crystal phase inversion to enhance permeability of thin film composite membrane

Thin film composite (TFC) membrane can get rid of small molecular contaminants and salts with a very high efficiency, thus exhibiting promising potential for addressing the emerging problem of a clean water shortage. In this work, a new type of TFC membrane was prepared by interfacial polymerization of two monomers (MPD and TMC) on surface of SiO₂/polyvinylidene fluoride (PVDF) substrate. The maximum flux of 3.16 L m⁻² h⁻¹ Bar⁻¹ was achieved for the optimized hydrophobic SiO₂ nanoparticles well dispersed in PVDF substrate, which is 2.6 times higher than that of 1.21 L m⁻² h⁻¹ Bar⁻¹ for the commercial cellulose triacetate reverse osmosis membrane. The improved performance of TFC membrane could be attributed to the higher compaction resistance of SiO₂/PVDF substrate. Further analysis revealed that PVDF crystal phase inversion induced by superhydrophobic SiO₂ nanoparticles obviously enhanced the intramolecular and intermolecular hydrogen bonds between PVDF polymer molecules. Additionally, the narrower finger-like pore size and thicker pore wall of SiO₂/PVDF substrate also played significant roles in enhancing the compaction resistance of PVDF membrane. This work also provides a proof-of-concept demonstration of high permeability substrates for effective flux enhancement of TFC membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48204.     

Compatibilization of PVDF/PA6 Blend by the Addition of a Third Polymer PTFE

The compatibilization of poly(vinylidene fluoride) (PVDF) with polyamide 6(PA6, higher acrylonitrile content) blend was improved by adding poly(methyl methacrylate) (PTFE). It was confirmed by characterizing the mechanical and tribological properties of the blends. More homogeneous morphology was formed when PTFE was added into PVDF/PA6 blend, which was shown in scanning electron microscopy (SEM). The surface tension of blends was increased due to the higher polar surface tension of PTFE. As the content of PTFE was increased further, the tensile strength of the blend was slightly decreased.     

Preparation and properties of peroxide dynamically vulcanized poly(vinylidene fluoride)/silicone rubber/zinc dimethacrylate composites

Composites of poly(vinylidene fluoride) (PVDF), silicone rubber (SR), and zinc dimethacrylate (ZDMA) were prepared via peroxide dynamic vulcanization. The effect of ZDMA loading on the morphology, mechanical properties, and rheology of the PVDF/SR/ZDMA composite was investigated. It was found that, some rubber particles with different diameters were aggregated and distributed in the PVDF matrix. The average diameters of rubber particles increased when ZDMA was incorporated into the PVDF/SR blend. A higher content of ZDMA seemed to show a favorable effect on the mechanical properties of PVDF/SR/ZDMA composites. The tensile strength, flexural strength, and flexural modulus of PVDF/SR/ZDMA composites decreased with increasing the ZDMA loading, which was due to the decreased tensile strength and total crosslink density of SR/ZDMA composite and the increased diameter of rubber particles, but the compatibility and interfacial interaction between PVDF phase and SR phase were obviously improved, which contributed to improved the Izod impact strength. In addition, the rheology analysis also suggested that interfacial adhesion between PVDF phase and SR phase was improved due to the incorporation of ZDMA. POLYM. COMPOS. 37:1093–1100, 2016. © 2014 Society of Plastics Engineers     

Temperature dependent dielectric properties of self‐standing and flexible poly(vinylidene fluoride) films infused with Er3+ doped GeO2 and SiO2 nanoparticles

The synthesis of Er³⁺@GeO₂ and Er³⁺@SiO₂ nanoparticle impregnated self‐standing poly(vinylidene fluoride) films by a facile solution casting technique has been reported. The prepared films were thoroughly characterized using X‐ray diffraction technique, field emission scanning electron microscopy, and transmission electron microscopy. The optical properties were evaluated using UV–Vis spectroscopy. Detailed study on the temperature dependent dielectric properties of the composite films with different Er³⁺ content were also investigated to establish the electrical properties of the same, which revealed the presence of different relaxation processes, namely, and ρ. Due to the smaller size, Er³⁺@SiO₂ was found to disperse better in the PVDF matrix than Er³⁺@GeO₂, which resulted in higher dielectric constant of the former at 300 K. At higher temperature (403 K), the behavior was reversed due to the formation of larger sized low mobility complexes. An investigation on ac conductivity proved the conduction mechanism for neat as well as composite PVDF films to follow the Correlated Barrier Hopping model. The loading of Er³⁺@GeO₂ and Er³⁺@SiO₂ nanoparticles in the PVDF matrix significantly enhances the dielectric properties without losing the flexibility of the composite films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44016.     

Novel composites of copper nanowire/PVDF with superior dielectric properties

Novel copper nanowires (CuNWs)/poly(vinylidene fluoride) (PVDF) nanocomposites with high dielectric permittivity (ε′) and low dielectric loss (ε″) were prepared by a precipitation technique followed by melt compression. Their dielectric properties over the broadband frequency range, i.e. 10¹–10⁶ Hz, were compared with multi-walled carbon nanotubes (MWCNT)/PVDF nanocomposites prepared by the same technique. It was observed that the CuNWs/PVDF nanocomposites had higher dielectric permittivity, lower dielectric loss and thus significantly lower dissipation factor (tan δ) than the MWCNT/PVDF nanocomposites at room temperature. This behavior was ascribed to a higher conductivity of the fresh core of the CuNWs relative to the MWCNT, which provided the composites with a higher amount of mobile charge carriers participating in the interfacial polarization. Moreover, the presence of oxide layers on the CuNWs surfaces diminished the conductive network formation leading to a low dielectric loss.     

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

The wetting resistance of poly(vinylidene fluoride) (PVDF) membrane is a critical factor which determines the carbon dioxide (CO₂) absorption performance of the gas–liquid membrane contactors. In this study, the composite PVDF–polytetrafluoroethylene (PTFE) hollow fiber membranes were fabricated through dry-jet wet phase-inversion method by dispersing PTFE nanoparticles into PVDF solution and adopting phosphoric acid as nonsolvent additive. Compared with the PVDF membrane, the composite membranes presented higher CO₂ absorption flux due to their higher effective surface porosity and surface hydrophobicity. The composite membrane with addition of 5 wt % PTFE in the dope gained the optimum CO₂ absorption flux of 9.84 × 10⁻⁴ and 2.02 × 10⁻³ mol m⁻² s⁻¹ at an inlet gas (CO₂/N₂ = 19/81, v/v) flow rate of 100 mL min⁻¹ by using distilled water and aqueous diethanolamine solution, respectively. Moreover, the 5% PTFE membrane showed better long-term stability than the PVDF membrane regardless of different types of absorbent, indicating that polymer blending demonstrates great potential for gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47767.     

High-performance PA1/TPU films with enhanced dielectric constant and low loss tangent

Polymer composites with high dielectric constant are promising materials for energy-storage application. However, their development has generally been hindered due to the challenge to balance dielectric constant and loss tangent. In this work, a novel thermoplastic polyurethane (TPU)-based composite with high dielectric constant and low loss tangent was prepared by inducing polyamide-1(PA1). The optimal content of PA1 in TPU matrix was 1.0 wt %. Importantly, the dielectric constant of TPU exhibited great stability at the frequency range of 10³–10⁶ Hz and increased sharply with the addition of PA1. In specific, the dielectric constant of TPU increased from 8 to 41 with the incorporation of 1.0 wt % PA1, which was five times higher than that of pure TPU. Meanwhile, the loss tangent still kept at a low level of less than 0.02. This work may provide a new direction for preparation of dielectric polymer composites with excellent comprehensive performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48469.     

Development of a novel PPTA/cellulose composite insulation paper with low dielectric constant and improved mechanical properties by BTCA crosslinking

This study investigates the effect of 1,2,3,4-butane tetracarboxylic acid (BTCA) crosslinking treatment on the electrical properties of poly-p-phenylene terephthalate (PPTA)/cellulose insulation paper to prepare a novel composite insulation paper with low dielectric constant and good electrical performance. Three-layer PPTA/cellulose composite paper crosslinked by BTCA under various conditions, composite paper without crosslinking, directly mixed composite paper, and conventional Kraft paper are prepared. The morphology and surface chemical composition of the paper samples are characterized. Dielectric, mechanical, and thermal properties are investigated. Results show that the BTCA concentration of 0.2 mol L⁻¹ with a 180°C curing temperature is the relatively superior crosslinking condition to prepare a novel composite with low dielectric constant and good comprehensive performance. The dielectric constant and loss of the novel composite paper decrease to 3.21 and 0.392 at 50 Hz. The tensile strength of the BTCA crosslinked three-layer PPTA/cellulose composite paper (thickness: 130 μm) has reached 10.01 kN m⁻¹, increased by 41.6% than the directly mixed composite paper. The novel BTCA crosslinked composite paper also shows improved thermal stability. The BTCA crosslinking proves to be a promising method to improve the dielectric properties and electrical performance of the PPTA/cellulose composite paper.     

Improved dielectric properties of poly(vinylidene fluoride)–BaTiO3 composites by solvent-free processing

Composites of poly(vinylidene fluoride) (PVDF) and BaTiO₃ nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent-free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·10⁴ Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents.