Copolymer Of Tetrafluoroethylene Research Articles

Molecular–topological structure of tetrafluoroethylene–perfluoromethylvinyl ether copolymer irradiated with MeV protons

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoromethylvinyl ether has been studied for the first time before and after irradiation with 1- and 4-MeV protons. The pseudo-network structure of the copolymer contains an amorphous block and crystalline segments of macromolecules as branching points. After bombardment with protons, a high-temperature amorphous block is formed in the copolymer with simultaneous complete amorphization of the copolymer structure and a decrease in its molecular flow temperature. The surface of a target plate with a thickness of 500 μm that has not been directly exposed to proton bombardment preserves the molecular–topological structure of the initial copolymer.

Triboelectrification‐Enabled Self‐Charging Lithium‐Ion Batteries

AbstractLi‐ion batteries as energy storage devices need to be periodically charged for sustainably powering electronic devices owing to their limited capacities. Here, the feasibility of utilizing Li‐ion batteries as both the energy storage and scavenging units is demonstrated. Flexible Li‐ion batteries fabricated from electrospun LiMn2O4 nanowires as cathode and carbon nanowires as anode enable a capacity retention of 90% coulombic efficiency after 50 cycles. Through the coupling between triboelectrification and electrostatic induction, the adjacent electrodes of two Li‐ion batteries can deliver an output peak voltage of about 200 V and an output peak current of about 25 µA under ambient wind‐induced vibrations of a hexafluoropropene–tetrafluoroethylene copolymer film between the two Li‐ion batteries. The self‐charging Li‐ion batteries have been demonstrated to charge themselves up to 3.5 V in about 3 min under wind‐induced mechanical excitations. The advantages of the self‐charging Li‐ion batteries can provide important applications for sustainably powering electronics and self‐powered sensor systems.

Features of the supercritical CO2-assisted immobilization of fluorinated tetraphenylporphyrins into tetrafluoroethylene copolymers

The immobilization of fluorinated tetraphenylporphyrins (FTPPs) into tetrafluoroethylene copolymers (fluoroplast F-42 and MF-4SK, a perfluorinated sulfonic acid cation exchanger in H+-form) is conducted in supercritical CO2 (scCO2). The effects the conditions of immobilization (the temperature and pressure of scCO2, reaction time, and the addition of cosolvents) and the structure of the carrier polymer have on the content of porphyrin in these polymers is studied. The porphyrin-loaded polymer systems are shown to exhibit photosensitizing activity in anthracene and cholesterol oxidation in scCO2. Under conditions of photocatalysis, chemical and functional stability is a feature of only MF-4SK polymer systems; this is attributed to the formation of protonated forms of the porphyrins and their interaction with SO3 −-groups of the polymer (an ion exchange process), which prevents leaching of the FTPP from the polymer matrix. The photocatalytic process actually occurs inside the matrix of the perfluorinated copolymer, with the protonated form of the porphyrin acting as a photosensitizer. The rate constant of anthracene photooxidation in the presence of FTPP-loaded MF-4SK films in scCO2 is found to pass through a maximum as a function of the porphyrin content and the polymer film thickness. The use of such catalytic systems for cholesterol photooxidation in scCO2 is shown to produce a virtual monoproduct (yield, ~10%): 6-formyl-B-norcholestane-3,5-diol, a compound with high biological activity.

Polyelectrolyte Nanocomposite Membranes Using Surface Modified Nanosilica for Fuel Cell Applications

ABSTRACTThe preparation and characterization of a new type of nanocomposite polyelectrolyte membrane (PEM), based on Nafion® (E. I. du Pont de Nemours and Co., Ltd., for its copolymer of tetrafluoroethylene and perfluorinated vinyl ether) and sulfonic acid (-SO3H) or phosphotungstic acid (PWA) modified nanosilica (Si-SO3H or Si-PWA, respectively), for direct methanol fuel cell (DMFC) applications are described. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy (SEM), water uptake, methanol permeability and ion exchange capacity, as well as proton conductivity. The Nafion®/Si-PWA and Nafion®/Si-SO3H membranes showed higher proton conductivity, lower methanol permeability and, as a consequence, a higher selectivity parameter, in comparison to the neat Nafion® or Nafion®/pristine nanosilica membranes. The obtained results indicated that both the Nafion®/Si-PWA and Nafion®/Si-SO3H membranes could be utilized as promising polyelectrolyte membranes for direct methanol fuel cell applications.

Effect of γ-irradiation on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) before and after γ-irradiation has been studied for the first time. The pseudo-network structure of the copolymer contains an amorphous block and the crystalline segments of macromolecules serve as branching points. After γ-irradiation to a dose of 15 to 2380 kGy, polyassociative cluster-type entities have appeared in the initial copolymer in place of the crystalline branching points with simultaneous structure amorphization and a decrease in the onset temperature of molecular flow.

Effect of γ-irradiation and thermal annealing on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) subjected to γ-irradiation and thermal annealing has been studied for the first time with the use of thermomechanical spectrometry. The pseudonetwork structure of the copolymer contains an amorphous block (interjunction chains) and crystalline segments (branching points). The diblock amorphous and crystalline structure with a crystal structure fraction of 0.21 transformed into an almost completely amorphous structure with a crystallite fraction of 0.06 after the irradiation of the copolymer at a dose of 600 kGy. Thermal annealing at 483 K formed a new structure: a high-temperature amorphous block.

Features of the molecular–topological structure of γ-irradiated powdered tetrafluoroethylene–perfluoro(propyl vinyl ether) copolymer

With the use of thermomechanical spectrometry in two modes, coaxial, when the load application vector is coplanar with the compacting pressure vector (semicrystalline copolymer) during the measurement of the deformation of a copolymer of tetrafluoroethylene with perfluoro(propyl vinyl ether), and mutually perpendicular (completely amorphous copolymer), it has been established that the axial compression of the copolymer brought its topological structure to an absolutely anisotropic state. After γ-irradiation, the semicrystalline structure of the copolymer was retained regardless of the radiation dose. The minimum values of the glass transition temperature of the amorphous block and the degree of crystallinity were observed in the copolymer irradiated to a dose of 150 kGy. The molecular weight distribution functions of interjunction chains in the networks of the amorphous blocks of the initial copolymer and its γ-irradiated analogs are bimodal.

Gaseous products of the bombardment of a tetrafluoroethylene–hexafluoropropylene copolymer with accelerated MeV protons

The action of 1- to 4-MeV protons on a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) in a vacuum is accompanied by the release of more than 25 gaseous products and a decrease in its thermal stability. During the course of proton bombardment, the predominant rupture of lateral C–CF3 bonds with the release of CF3 particles occurs along with the detachment of fluorine and hydrogen atoms yielding H2 and HF. Unlike polytetrafluoroethylene, a distinctive feature of the radiolysis of FEP is a decrease by a factor of 5 in the probability of fluorine detachment from the FEP macromolecule by accelerated protons.

(Plenary) Development of PFSA Ionomers and Their Use in Fuel Cells

Widespread of fuel cells are strongly desired from the point of reducing the GHG and for clean environment. In order to achieve these, reducing the cost of the fuel cell vehicle is needed and from this point, higher operating temperatures of PEFC can contribute for designing compact and simple cooling system. We have been developing variety of new Perfluorosulfonic acid (PFSA) ionomers having high ion exchange capacity (IEC) and other properties required for each the membrane and the electrolyte in the electrodes. The ionomer with high proton conductivity was tested by copolymerization of tetrafluoroethylene with a new bifunctional fluorosulfonyl monomer 1. The ion exchange capacity was 1.58 meq/g and the water uptake after immersion in hot water at 80 °C for 16 hours was much lower compared to that of conventional ionomer. Reduction in Pt loading in the cathode is another requirement for PEFC to reduce the cost. Especially at higher temperature and lower RH conditions under which the flux of oxygen to the Pt surface through the ionomer in the electrode could be the rate limiting factor for the oxygen reduction reaction (ORR). In order to increase the oxygen flux to Pt surface, the use of ionomers having higher oxygen permeability can be a solution. We have designed and synthesized various ionomers based on a general rule that the lower the density of a fluorinated polymer, the higher the oxygen permeability. One of the newly prepared ionomer having lower density showed more than 2 times higher the oxygen permeability 2 at low RH conditions. The use of this high oxygen permeable ionomer at cathode showed the possibility of achieving the same cell voltage with half the amount of Pt loading.We see that the ionomer plays an important row in developing PEFC achieving the requirements from the market. The ionomer can also be used in the micro porous layers (MPLs) between the catalyst layers and the Gas diffusion substrate to create hydrophilic MPLs. Conventionally, hydrophobic MPLs were applied between the GDM and the catalyst layer to prevent flooding due to excess water in the electrode. But the hydrophobicity of the MPL is not favorable when the cell is operating under a dry condition. We have been reporting the use of hydrophilic MPL between the GDM and the catalyst layer 3. It can control the water balance in the MEA, achieving higher performance under low RH conditions without facing the low performance due to mass transfer issue at wet conditions. This hydrophilic MPL was used in the cathode in combination with a high proton conductive membrane, and the MEA showed excellent performance under a very dry condition. We are continuously making efforts developing PEFC materials getting into the next stage.

The investigation of the production method influence on the structure and properties of the ferroelectric nonwoven materials based on vinylidene fluoride – tetrafluoroethylene copolymer

In the present work the production method influence (solution blow spinning and electrospinning) on the structure and properties of the ferroelectric nonwoven materials based on VDF-TeFE copolymer is investigated. It was shown that the nonwoven materials obtained by electrospinning have smooth cylindrical-shaped fibers with a narrow diameter distribution, whereas the nonwoven materials produced by solution blow spinning are characterized by multi-level spatial organization with the fibers having their own advanced morphology. By using DSC and XRD analysis it was found that the nonwoven materials obtained by electrospinning have higher content of the electrically active phases. Also these materials have higher strength owing to their morphological and structural features. It was shown that both types of nonwoven materials are non-toxic. A higher adhesion of stem cells and cells from EA-hy 926 cell line to nonwoven materials produced by solution blow spinning was observed.

Ultralow wear Perfluoroalkoxy (PFA) and alumina composites

Fluoropolymers have unique mechanical, chemical, and tribological properties (low friction coefficients) but their use as solid lubricants is inhibited by high wear rates (1–5×10−4mm3/Nm). The addition of certain types of α-alumina has been shown to reduce the wear rate of PTFE by over three orders of magnitude, but due to its extremely high molecular weight PTFE cannot be screw injection molded. However, PFA, a perfluorinated copolymer of tetrafluoroethylene (TFE) and a perfluorinated alkylvinyl ether (PAVE), can be. Teflon® PFA 340 samples with various weight fractions of α-alumina (0%, 5%, 7.5%, 10%) were injection molded, and samples from each mold were wear tested against stainless steel (P=6.3MPa, v=50.8mm/s). Experiments showed that the friction behavior of the PFA 340-α alumina composite was very close to that of both unfilled PFA 340 and PTFE-α alumina composites. The wear rate of unfilled PFA 340 was 1.4×10−4mm3/Nm, and dropped to 4.0×10−8mm3/Nm for the PFA-α alumina composites. Just as in the case of PTFE-α alumina composites, these PFA composites generated brown-colored tribofilms on both the polymer and metal surfaces, which were indicative of tribochemical changes. ATR-IR and FTIR spectra of each surface showed evidence for the generation of perfluorinated carboxylate salts and waters of hydration. This spectral similarity between PTFE and PFA 340 samples shows that the same tribological mechanism found in PTFE-α alumina composites is responsible for ultralow wear in PFA-α alumina composites as well.

Ferroelectric properties of vinylidene fluoride/tetrafluoroethylene copolymer thin films consisting of needle-like crystals

Unique ferroelectric vinylidene fluoride (VDF)/tetrafluoroethylene (TeFE) copolymer thin films consisting of needle-like crystals were formed using Au-sputtered substrates. The VDF/TeFE films with a mixing ratio of mol % were melted at 170 °C for 30 min and then recrystallized at 116 °C for 300 min. The molecules in the resultant needle-like crystals had a β-phase form and showed 200/110 orientation, while the direction of each needle-like crystal was random in-plane. The remanent polarization of the 450-nm-thick VDF/TeFE films consisting of the needle-like crystals were estimated to be 62 mC/m2 from the electric displacement vs electric field (D–E) hysteresis measurement at the applied field of 156 MV/m and the frequency of 10 Hz. The remanent polarization of 62 mC/m2 was approximately 50% larger than that of conventional VDF/TeFE films consisting of plate-like crystals.

An effect of the electrode material on space charge relaxation in ferroelectric copolymers of vinylidene fluoride

Processes of relaxation of space charges formed by impurities carriers in isotropic films of vinylidene fluoride and tetrafluoroethylene copolymers of the composition 71/29 and 94/6 were studied. Al and Au symmetric electrodes deposited by evaporation in vacuum have been used. In the case of Al electrodes at temperatures above 100 °C, giant low frequency dielectric dispersion was observed, while it is absent in films with Au electrodes. Causes of this phenomenon were studied by the X-ray photoelectron spectroscopy. It was shown that at Al deposition, new functional groups, such as Al-C, Al-F, and Al2O3, which are not characteristic of the copolymer film surface, formed. They were supposed to be traps for impurity carriers and because of this the electrode became partially blocked. This led to appearance of the giant electrode polarization on the metal-polymer boundary, which did not take place in the case of Au electrodes. Parameters of the Au4f line for the copolymer with different contents of fluorine atoms in the chain were analyzed. An increase in the number of these atoms was shown to result in the line shift to higher energies. This phenomenon was associated with an increase in the shift of the electron density from Au atoms to the F ones which has a high affinity to electrons.

Preparation of Hyflon AD60/PVDF composite hollow fiber membranes for vacuum membrane distillation

Abstract Hydrophobic membrane is desired to avoid pore wetting phenomenon in membrane distillation (MD). In the present paper, highly hydrophobic Hyflon AD60/PVDF composite hollow fiber membranes were prepared by coating a copolymer (Hyflon AD60) of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD) on poly(vinylidene fluoride) (PVDF) membranes. The effects of Hyflon AD60 concentration, coating time, heat-treatment temperature and heat-treatment time on the structures and performances of Hyflon AD60/PVDF composite hollow fiber membranes in vacuum membrane distillation (VMD) process were investigated. The results show that the hydrophobicity of PVDF hollow fiber membrane was significantly improved by coating Hyflon AD60. The optimized Hyflon AD60 concentration, coating time, heat-treatment temperature and heat-treatment time were 0.1 wt%, 10–20 min, 40–50 °C and 9 h, respectively. Employing NaCl solution with concentration of 35 g × L−1, under a vacuum of 0.09 MPa and feed temperature of 70 °C, the water flux and salt rejection of the composite hollow fiber membrane in VMD process reached to approximately 10 kg × m−2 × h−1 and higher than 99.9 %, respectively, and kept stable, indicating that Hyflon AD60/PVDF composite membrane is an excellent candidate for operation in VMD operation.

Influense of the high-voltage conductivity on peculiarity of polarization ferroelectric polymer on based vinylidenefluoride

The phenomena of high-voltage polarization and conductivity in oriented vinylidenefluoride and tetrafluoroethylene copolymer films have been investigated. It was shown that under certain electric fields, injection of carriers from the material of electrodes appears The barrier for holes injection in the copolymer was found to be lower than that for electrons. It results in more effective screening of the external field near the anode than near cathode. Electrones, ejected from cathode, creating negative charge by trapping on the surface. It is shown that the electrons injected from cathodes create a negative homocharge on the copolymer surface and then become captured on the surface shallow traps. Their nature has been studied by the x-ray photoelectron spectroscopy. It was shown that these traps may consist of chemical defects in the form of new functional groups formed by reactions of surface macromolecules with sputtered atoms of aluminum. The asymmetric shape of hysteresis curves was explained by the difference in mobility of injected holes and electrons. These factors caused appearance of "non-closed" hysteresis curves for fluorine-containing polymer ferroelectrics. Hysteresis phenomena observed at low electric fields (below coercive ones) are to associate with the behavior of the domains localized in the ordered regions formed during secondary crystallization of copolymers.

Flow property at capillary extrusion for ethylene–tetrafluoroethylene copolymer

Abstract The capillary extrusion property of ethylene–tetrafluoroethylene copolymer (ETFE) is evaluated. It is found that ETFE shows several types of flow instabilities. The shark-skin failure is observed over the first critical shear stress 7.9 × 10 4 Pa. Then, the slip-stick instability is detected at 1.8 × 10 5 Pa, which corresponds to the critical stress of the slippage at the die wall, evaluated by the Mooney method. Moreover, gross wavy melt fracture appears at high out-put rate condition. It is interesting to note that quasi-stable flow region; so-called “super-extrusion”, is observed between slip-stick and wavy melt fracture regions. Because of the steady slippage, ETFE can be extruded at a high out-put rate condition without surface roughness and distortion of extrudates.

Functional Recovery of Carbon Nanotube/Nafion Nanocomposite in Rat Model of Spinal Cord Injury

Background Acute spinal cord injury (ASCI) can lead to paraplegia or quadriplegia, the treatment of which has been a major problem. New therapeutic approaches in developing carbon nanotubes (CNT) functionalized with the Nafion nanocomposite, a sulfonated tetrafluoroethylene copolymer, have been shown to increase the length of selected neurites in vitro. Objective We hypothesized that the administration of the CNT/Nafion nanocomposite after experimental SCI will promote regeneration of axons into the lesion cavity and the functional recovery of the hind limbs in a rat model. Methods To evaluate this hypothesis through this experimental research paper, transection SCI was induced at the T9-T10 vertebral level in adult female rats. One week after transection, the epicenter of the lesion was injected with 25 lL of vehicle (saline), or 1 lg/mL, 10 lg/mL, or 100 lg/mL of CNT/Nafion nanocomposite. Behavioral analysis was carried out by assessing tail flick, chronic pain or mechanical allodynia, motor coordination, and the results of the rotarod test performed pre- and post-surgery, on days 3, 7, 14, 21 and 28, using the tail flick analysis, Noldus CatWalk gait analysis, open-field locomotor test, and Rotarod test. At 28 days post-injection, the rats were euthanized and spinal cord tissue was extracted. Results We found that post-SCI, administration of the CNT/Nafion nanocomposite resulted in decreased lesion volume, increased neurofilament-positive fibers and corticospinal tract fibers in the lesion, and no increase in reactive gliosis (P < 0.001). Additionally, post-SCI administration of CNT/Nafion nanocomposite induced a modest improvement in hind limb locomotor recovery without inducing hyperalgesia. Conclusion These data suggest that the CNT/Nafion nanocomposite may be an effective material to promote axonal repair and regeneration after SCI.

Structure and properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation

Properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation in a turbulent gas flow are investigated in the paper. By means of scanning microscopy, it is shown that synthesized nonwoven materials are characterized by high porosity and complicated spatial organization. By means of X-ray diffraction, infrared spectroscopy, combination scattering spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, it is shown that fibers that form the nonwoven material are characterized by a crystal structure typical of ferrielectric phases. The quantitative content of residual solvents in the formed materials is determined. By using a mobile cell culture, it is shown that the produced nonwoven materials are not toxic and can be used for medical purposes.

Chemical modification of Hyflon® AD copolymer end groups by means of physical and chemical treatments. A joint spectroscopic and quantum chemical investigation

In this paper is presented a study on the effects of physical treatments, namely electron beam irradiation or fluorination, on a perfluoropolymer copolymer of tetrafluoroethylene with 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (Hyflon® AD copolymer). The analysis has been carried out by means of IR spectroscopy and quantum chemical modeling based on density functional theory; this combined experimental/theoretical approach has proven effective for the interpretation of previously unassigned IR bands, which are associated to functional groups generated by polymer degradation and chain scission. We performed a systematic screening of chemical groups and structures compatible with degradation pathways that are possible from the chemical point of view: the chemical mechanisms and the correlation with the spectroscopic experimental data (both frequency and intensity) provide guidelines in understanding the phenomena. Moreover, the spectroscopic experimental/theoretical and chemical approaches allowed us to identify some chemical structures responsible for the unassigned IR bands in the CO stretching frequency region above 1800cm−1, which is typical for carbonyl groups in fluorinated systems.

Local piezoelectric response, structural and dynamic properties of ferroelectric copolymers of vinylidene fluoride–tetrafluoroethylene

The characteristics of the local piezoelectric response of isotropic films of copolymers of vinylidene fluoride (VDF) were compared with 6 and 29 mol% tetrafluoroethylene (TFE) obtained by crystallization from a solution in acetone. Time dependence of the electric displacement response was analyzed after switching of the spontaneous polarization. A copolymer with a higher content of tetrafluoroethylene is characterized by higher values of electrical displacement and piezoelectric response. For interpretation of this fact, we used molecular mobility in amorphous phase dates. It is shown that the activation energy of local and cooperative liquid-like (in the amorphous phase) mobility is markedly lower in the copolymer with a higher content of TFE. Under identical conditions of the crystallization, both films of the copolymers lead to the formation of larger crystals of the polar phase and magnitude of a “long” period at a high content of copolymer of TFE. It is postulated that these structural parameters are responsible for the stable value of residual local piezoelectric activity. It is found that the rapid decay of the signal in the local piezoresponse of polarized films is controlled by the activation energy of the local and cooperative dynamics chains of the amorphous phase.