Tetrafluoroethylene Research Articles

TFE Terpolymers: Once Promising - Are There Still Perspectives in the 21st Century? Part II: Processing, Properties, Applications.

Tetrafluoroethylene (TFE) terpolymers have emerged as advantageous substitutes for polytetrafluoroethylene (PTFE). Therefore, they are being considered as alternatives to PTFE in many application areas. The advantages of TFE terpolymers include their facile processability at elevated temperatures, their solubility in some polar organic solvents, their inertness against aqueous acids, aqueous bases and a large number of mostly nonpolar organic solvents, their low dielectric constant, their low refractive index as well as useful electro- and thermochemical properties. This review on TFE terpolymers focuses on their processing including shaping and surface modification as well as on selected properties including wettability, dielectric properties, mechanical response behavior, chemical stability, and degradability. Applications including their use as elastomeric sealing material, liner and cladding layer as well as their use as material for membranes, microfluidic devices, photonics, photovoltaics, energy storage, energy harvesting, sensors, and nanothermitic composites will be discussed. The review concludes with a discussion of the future potential of TFE terpolymers and scientific challenges to be addressed by future research on TFE terpolymers.

TFE Terpolymers: Once Promising - Are There Still Perspectives in the 21st Century: Synthesis, Characterization, and Properties-Part I.

Polytetrafluoroethylene (PTFE) exhibits outstanding properties such as high-temperature stability, low surface tension, and chemical resistance against most solvents, strong acids, and bases. However, these traits make it challenging to subject PTFE to standard polymer processing procedures, such as thermoforming and hot incremental forming. While polymer processing at temperatures above the melting point of PTFE is already demanding, the typically large molar mass of PTFE results in extremely high melt viscosities, complicating the processing of PTFE. Also, PTFE tends to decompose at temperatures close to its melting point. Therefore, fluoropolymers obtained by copolymerizing tetrafluoroethylene (TFE) with various co-monomers are studied as alternatives to PTFE (e.g., fluorinated ethylene-propylene (FEP)), combining its advantages with better processability. TFE terpolymers have emerged as desirable PTFE alternatives. This review provides an overview of the synthesis with various comonomers and microstructural analysis of PTFE terpolymers and the relationships between the microstructures of TFE terpolymers and their properties.

Thermal desorption – gas chromatography – mass spectrometry (TD-GC-MS) analysis of PFAS used in food contact materials

Per- and polyfluoroalkyl substances (PFAS) are used in food contact materials (FCMs), e.g. as production aids in the fabrication of PTFE based coatings for kitchenware or as additives in paper and board. Growing concerns about the environment and health related to PFAS have led to an increasing interest in monitoring PFAS levels in FCMs as well as their migration into food. In this study, method development for the analysis of PFAS by thermal desorption – gas chromatography – mass spectrometry (TD-GC-MS) was done. In addition to fluorotelomer alcohols (FTOHs), which are the only PFAS commonly analysed by GC-MS, it was proven that perfluorocarboxylic acids (PFCAs) and per- and polyfluoroether carboxylic acids (PFECAs) as well as their thermolysis products, perfluoroethers (PFEs) and perfluoroalkenes, can be analysed by GC-MS without prior derivatization. Screening for PFCAs and FTOHs was possible by electron impact ionization (EI) using group specific SIM fragments. Confirmation of identity has been done by EI scans as well as chemical ionization (CI) SIM measurements. LODs (limits of detection) of PFCAs, FTOHs and PFECAs in the TD-GC-MS instrument were in the low pg range. Thermal degradation of PFCAs and PFECAs during TD-GC-MS measurement was investigated.

Investigating the electronic properties of PANI/graphene/PVDF/PTFE nanocomposite

Manufacturing of clean energy is an important topic of research for modern life. This paves the way toward investigating easy manufacturing; high-performance energy storage materials. In this sense, conducting polymers such as polyaniline (PANI) are modified with graphene (G) then bound with poly vinylidene fluoride (PVDF) and poly tetrafluoro ethylene (PTFE) to enhance their electronic properties to be used as electrode material in energy storage applications. Furthermore, molecular modeling based on density functional theory at B3LYP/LanL2DZ level of theory was utilized to study the interaction between PANI; G; PVDF and PTFE. Some important properties are calculated such as the total dipole moment (TDM), HOMO/LUMO energy gap (ΔE), and molecular electrostatic potential (MESP). TDM of PANI was found to be 3.994 Debye and increased to 6.010, 9.012, and 9.822 Debye for PANI/G/PTFE, PANI/G/PVDF/PTFE, and PANI/G/PVDF, respectively. ΔE of PANI is 4.353 eV and decreased because of the interaction of PANI with G and polymer binders to reach 3.507, 3.095, and 2.127 eV for PANI/G/PTFE, PANI/G/PVDF, and PANI/G/PVDF/PTFE, respectively. From MESP result, the reactivity and electronic properties increased with the interaction of PANI with G and polymer binders. PANI/G/PVDF/PTFE composite was dedicated as the most suitable candidate for electrode material for many applications.

The Simulation and Optimization of the Tetrafluoroethylene Rectification Process

In the R22 (chlorodifuoromethane) steam-cracking process, which is used to produce a TFE (tetrafluoroethylene) monomer, distillation is employed to separate the high-purity TFE monomer from the cracked gas generated during this procedure. Traditionally, this distillation process is carried out using five towers. In this study, the traditional five-tower distillation method was transformed into a four-tower distillation method through the Aspen Plus simulation software, and this process was simulated and optimized. Meanwhile, a double-effect distillation process was designed for the transformed four-tower distillation process. The transformed distillation process not only meets the requirements of 99.999% purity for the TFE monomer and 99.99% purity for R22 recycling, but it also reduces the footprint by eliminating one distillation tower and saves 112.9002 kW of tower load, thus reducing the operating costs. This research provides valuable guidance for practical production.

Separation of CO2 and TFE by using diethanolamine and diisopropylamine

ABSTRACT The near-azeotrope mixture of TFE and CO2 is an important concern urging the scientific community to develop new ways for TFE/CO2 separations. In this work, for the first time, Diisopropylamine (DIPA) and Diethanolamine (DEA) are used as solvents for separating a near-azeotropic mixture of CO2 and tetrafluoroethylene (TFE). The complete separation mechanism has been analyzed using ASPEN Plus process simulator. The binary parameters for CO2, TFE, DIPA and DEA have been taken from Cosmotherm software and the pure data parameters have been taken from the literature (NIST). The validation of the processes has been completed by comparing binary parameters with literature and pure parameters with the UNIFAC data. The separation of the near-azeotropic mixture of TFE and CO2 has been investigated where, both solvents can be proposed as good candidates, however DEA is proven better performer than DIPA. In addition, CO2 emissions analysis and Total Annual Cost (TAC) analysis has been performed for the payback period of 3, 5 and 7 years, where DEA proves to be most efficient for TAC while DIPA has less CO2 emissions.

Gas Transport Properties of Vinylidene Fluoride-Tetrafluoroethylene Copolymers

The influence of the content of tetrafluoroethylene (TFE) groups on the gas transport properties of vinylidene fluoride (VDF) and tetrafluoroethylene copolymers has been studied. Experimental values of the permeability coefficients P and diffusion coefficients D for gases H2, He, N2, O2, CO2, as well as lower hydrocarbons CH4, C2H4 and C2H6 were measured and their solubility coefficients S were calculated. The values of the solubility coefficients of CO2 and C2H4 were found to deviate from the linear correlation of lg S on the Lennard-Jones potential. An explanation of this effect was proposed based on facilitated transport models. It was demonstrated that an increase in the content of TFE groups leads to a significant increase in the permeability coefficients of the penetrants studied mainly due to an increase in their diffusion coefficients. So, the permeability coefficient of helium and hydrogen increases approximately in 2.5 times, for carbon dioxide in 3 times, for argon, oxygen, methane and ethylene in 3.5 times, and for nitrogen and ethane in 4.4 times, respectively. These gas separation parameters in combination with good film-forming properties and commercial availability allows us to consider the studied VDF-TFE copolymers as promising materials for the fabrication of composite gas separation membranes.

Hybrid-modeling for PTFE polymerization reaction with deep learning-based reaction rate model

Abstract The tetrafluoroethylene (TFE) polymerization process is an essential industrial process to produce polytetrafluoroethylene (PTFE), which is extensively utilized in aerospace and medical domains. A precise mechanism model is a prerequisite for comprehensively understanding this process. However, significant uncertainties in the kinetic model parameters may hinder attaining an optimal reaction rate. This study proposes a hybrid polymerization reaction model that integrates process mechanism modeling and data-driven modeling to address this challenge. In the hybrid modeling approach, the mechanism model for the polymerization reaction is developed based on reaction kinetic and thermodynamic assumptions. Additionally, a long short-term memory (LSTM) neural network is employed to predict the reaction rate for chain initiation by leveraging temporal relationships derived from archived measurements. The proposed methodology is implemented using a PTFE polymer reactor system, and experimental comparisons affirm its superior performance and effectiveness.

Interrogation of PDD polymer and PDD-co-TFE copolymer microstructure by nuclear magnetic resonance spectroscopy

Teflon™ AF is a high temperature amorphous fluoropolymer manufactured by The Chemours Company composed of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) and tetrafluoroethylene (TFE) exhibiting one of the lowest dielectric constants of any polymer. While physical properties are observed to change with the ratio of TFE to PDD incorporated in the polymer, interrogation of structure is limited due to its rigid structure, the amorphous nature of the material at higher PDD concentrations, and its limited solubility. Solution state 19F NMR of the dissolved polymer, however, allows the fine structure and stereochemistry of the polymer to be interrogated. Solid state NMR eliminates solubility as a concern, but line shapes are significantly broadened limiting resolution. In this study samples with different PDD: TFE molar ratios have been interrogated by solution and solid state NMR.

Synthesis and Properties of the Novel High-Performance Hydroxyl-Terminated Liquid Fluoroelastomer.

Functional liquid fluoroelastomers are in high demand in new energy fields. And these materials have potential applications in high-performance sealing materials and as electrode materials. In this study, a novel high-performance hydroxyl-terminated liquid fluoroelastomer (t-HTLF) with a high fluorine content, temperature resistance, and curing efficiency was synthesised from a terpolymer of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), and hexafluoropylene (HFP). A carboxyl-terminated liquid fluoroelastomer (t-CTLF) with controllable molar mass and end-group content was first prepared from a poly(VDF-ter-TFE-ter-HFP) terpolymer using a unique oxidative degradation method. Subsequently, an efficient "one-step" reduction of the carboxyl groups (COOH) in t-CTLF into hydroxyl groups (OH) was achieved via the functional-group conversion method using lithium aluminium hydride (LiAlH4) as the reductant. Thus, t-HTLF with a controllable molar mass and end-group content and highly active end groups was synthesised. Owing to the efficient curing reaction between OH and isocyanate groups (NCO), the cured t-HTLF exhibits good surface properties, thermal properties, and chemical stability. The thermal decomposition temperature (Td) of the cured t-HTLF reaches 334 °C, and it exhibits hydrophobicity. The oxidative degradation, reduction, and curing reaction mechanisms were also determined. The effects of solvent dosage, reaction temperature, reaction time, and ratio of the reductant to the COOH content on the carboxyl conversion were also systematically investigated. An efficient reduction system comprising LiAlH4 can not only achieve an efficient conversion of the COOH groups in t-CTLF to OH groups but also the in situ hydrogenation and addition reactions of residual double bonds (C=C) groups in the chain, such that the thermal stability and terminal activity of the product are improved while maintaining a high fluorine content.

Application of homemade portable gas chromatography coupled to photoionization detector for the detection of volatile organic compounds in an industrial park

Traditional offline detection of volatile organic compounds (VOCs) requires complex and time-consuming pre-treatments including gas sampling in containers, pre-concentrations, and thermal desorption, which hinders its application in rapid VOCs monitoring. Developing a cost-effective instrument is of great importance for online measurement of VOCs. Recently, photoionization detectors (PID) are received great attention due to their fast response time and high sensitivity. This study a portable gas chromatography coupled to PID (pGC-PID) was developed and optimized experimental parameters for the application in online monitoring of VOCs at an industrial site. The sampling time, oven temperature and carrier gas flow rate were optimized as 80 s, 50 °C and 60 ml·min−1, respectively. The sampling method is direct injection. Poly tetra fluoroethylene (PTFE) filter membranes were selected to remove particulate matter from interfering with PID. The reproducibility and peak separation were good with relative standard deviations (RSD) ≤ 7%. Good linearities of 27 VOCs standard curves were achieved with R2 ≥ 0.99, and the detection limits were ≤10 ppb with the lowest being 2 ppb for 1,1,2-Trichloroethane. Finally, the pGC-PID is successfully applied in online VOCs monitoring at an industrial site. A total of 17 VOCs species was detected and their diurnal variations were well obtained, indicating pGC-PID is well suited for online analysis in field campaign.

Perfluoro Macrocyclic Ether as an Ambifunctional Additive for High‐Performance SiO and Nickel 88%‐Based High‐Energy Li‐ion Battery

AbstractState‐of‐the‐art lithium (Li)‐ion batteries employ silicon anode active material at a limited fraction while strongly relying on fluoroethylene carbonate (FEC) electrolyte additive exceeding 10 wt.% to enable stable cycling. The swelling issue of silicon in the aspect of solid electrolyte interphase (SEI) instability and a risk of safety hazards and high manufacturing cost due to FEC has motivated the authors to design a well‐working fluorinated additive substitute. High‐capacity cells employing nickel‐rich oxide cathode are pursued by operating at > 4.2 V versus Li/Li+, for which anodic stability of electrolyte is required. Herein, a highly effective new ambifunctional additive of icosafluoro‐15‐crown 5‐ether is proposed at a little fraction of 0.4 wt.% for the stabilized interfaces and reduced swelling of high capacity (3.5 mAh cm−2) 5 wt.% SiO‐graphite anode and LiNi0.88Co0.08Mn0.04O2 cathode. Utilizing together with a lowered fraction of FEC, reversible long 300 cycles at 4.35 V and 1 C (225 mA g−1) are achieved. Material characterization results reveal that such stabilization is derived from the surface passivation of both anode and cathode with perfluoro ether, LiF, and LixPFy species. The present study gives insight into electrolyte formulation design with lower cost and both‐side stabilization strategies for silicon and nickel‐rich active materials and their interfaces.

Continuous Counter-Current Multistage Microextraction in a Novel Tube-In-Tube Microextractor

Counter-current operation has been widely applied to enhance the extraction efficiency for systems with low distribution coefficients, which was hindered in microextraction because viscous force and surface tension dominate over gravity and inertial force. In this study, a novel design of a tube-in-tube microextractor relying on a poly tetra fluoroethylene membrane to construct a stable interface was proposed to conduct continuous counter-current extraction. Extraction kinetics for two systems with different distribution coefficients, membranes with different pore radii, and three flow rate ratios were measured as a function of residence time. For the system that toluene was used to extract 0.06 wt % phenol in water, 4.1 stages of extraction efficiency were achieved at a residence time of 9.8 min. A challenging case study (50 wt % acetone–water–toluene) was subsequently conducted to prove the high applicability for emulsion systems of this special microextractor. Lastly, a mathematical model was established and the predicted results of three flow rate ratios are in good agreement with experimental results.

Гидрофобизация пленок целлюлозы, полученной из стебля борщевика Сосновского, растворами теломеров тетрафторэтилена

The process of obtaining cellulose from the Sosnowsky hogweed stem and spathellas from this cellulose is described in detail. The task is relevant from the point of view of the use of this weed. The elemental composition and properties of the obtained cellulose samples were studied by elemental analysis, infrared (IR) spectroscopy, X-ray powder diffractometry, differential scanning calorimetry (DSC), and X-ray photoelectron spectroscopy (XPS). The study of IR spectra and X-ray patterns of cellulose made it possible to determine the degree of its crystallinity (65…75 %). The glass transition temperature (105…108 °C) of the samples was estimated from the results of DSC. A comparative analysis of the characteristics of the obtained cellulose with the available literature data was carried out. The treatment of spathellas obtained from cellulose with solutions of radiation-synthesized tetrafluoroethylene (TFE) telomers made it possible to obtain a hydrophobic material with a contact angle exceeding 140°. For hydrophobization, we used TFE telomers synthesized in acetone, the binary solvent Freon 113 + ammonia, and Flutec PP3, which have different terminal groups. It has been established that the interfacial angle of the surface of a cellulose spathella treated with telomers depends both on the composition (end groups) of the telomer and on the initial concentration of TFE at which the synthesis was carried out. The optimal concentration of TFE for the synthesis of telomers in Flutec PP3 has been determined. The presence of a fluoropolymer coating of the spathella, which ensures its hydrophobicity, was confirmed by XPS results.

Effects of friction pendulum bearing wear on seismic performance of long-span continuous girder bridge

To clear the wear effect of friction pendulum bearings (FPBs) on the seismic performance of multiple long-span continuous girder bridges, the rapid sliding performance test of the FPBs was carried out to get the wear degree of the modified poly tetra fluoroethylene (PTFE) wear plates. Taking a 6×110 m long-span continuous girder bridge as the engineering background, the seismic response of the bridge with different wear degrees of the FPBs was analyzed. The results show that the modified PTFE wear plate of the FPBs was severely worn in the rapid sliding performance test, and the friction coefficient was first increased to 0.09 and then decreased to 0.016. When the maximum displacement was reached, the bearing collided with the limitation block. Moreover, the internal forces of the critical pier were increased, and the bottom of the piers entered plasticity due to the wear of the FPBs. Due to the change in the seismic performance of the bridge, it is suggested that the rapid sliding performance of FPBs should be tested to ensure the structure safety of the long-span continuous girder bridge in rare earthquakes.

Formation of composite coatings: morphology and composition studies

In this work, composite fluoropolymer-containing coatings were obtained on samples of AMg3 aluminium alloy, MA8 magnesium alloy, and VT1-0 commercially pure titanium treated by plasma electrolytic oxidation (PEO). Superdispersed polytetrafluoroethylene (SPTFE) and a solution of tetrafluoroethylene (TFE) telomers in acetone were applied onto preliminarily formed PEO layers by the spray-coating method. The obtained coatings contained a large amount of crystalline polytetrafluoroethylene embedded in the outer porous layer of the PEO coating and did not have visible defects, which indirectly indicates high protective properties.

Design and characterization of molecular, crystal and interfacial structures of PVDF-based dielectric nanocomposites for electric energy storage.

PVDF-based polymers with polar covalent bonds are next-generation dielectric materials for electric energy storage applications. Several types of PVDF-based polymers, such as homopolymers, copolymers, terpolymers and tetrapolymers, were synthesized by radical addition reactions, controlled radical polymerizations, chemical modifications or reduction with the monomers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE). Owing to rich molecular structures and complicated crystal structures, PVDF-based dielectric polymers can show versatile dielectric polarization properties, including normal ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics and linear dielectrics, which are beneficial for designing polymer films with high capacity and high charge-discharge efficiency for capacitor applications. Furthermore, to satisfy the requirements of practical high-capacity capacitors, the polymer nanocomposite method is another promising strategy to achieve high-capacitance dielectric materials by the addition of high-dielectric ceramic nanoparticles, moderate-dielectric nanoparticles (MgO, and Al2O3), high-insulation nanosheets (BN), etc. It is concluded with the current problems and future perspectives of interfacial engineering, such as core-shell strategies and hierarchical interfaces in polymer-based composite dielectrics for high-energy-density capacitor applications. In addition, an in-depth understanding of the roles of interfaces on the dielectric properties of nanocomposites can be achieved by indirect analysis techniques (theoretical simulation) and direct analysis techniques (scanning probe microscopy). Our systematic discussions on molecular, crystal and interfacial structures provide guidance for designing fluoropolymer-based nanocomposites for high-performance capacitor applications.

A critical review on the material aspects of triboelectric nanogenerators (TENG)

Triboelectric nanogenerators (TENG) take the advantage of coupling effect for harvesting energy in the area of electronics for various self-powered applications. These nanogenerators are capable of converting energy in our surroundings into electrical energy by using the process of electrostatic induction and contact electrification. Triboelectric layers of a TENG are formed basically with the use of various polymers, metals and other inorganic materials like PTFE (Poly tetra fluoro ethylene), PDMS (polydimethyl siloxane), FEP (Fluorinated ethylene propylene) and Kapton. Selection of different materials for the device fabrication is very important since it contribute towards the triboelectric effect and also forms the fundamental structure for the proposed TENG device. In this review article, we emphasis mainly on various triboelectric materials considering factors such as stability, flexibility, power density etc., to improve upon the electrical output of the devices for different applications.

Confined Oxygen Promotes Radical Generation for Methane Oxidation Toward Liquid Oxygenates

The activation of methane (CH4) gas to produce value-added liquid hydrocarbons has been a challenging issue in catalytic research. Electrochemical oxidation is one of the alternative methods to oxidize methane and can be usually performed at ambient temperature, which can solve the problems of methane steam reforming caused by high temperature. However, electrochemical direct methane oxidation still have limitations that it should competes with oxygen evolution reaction, resulting in low efficiency. Also, oxygenates generated from methane oxidation can be easily overoxidized to carbon dioxide which is not appropriate product for the purpose of electrochemical system to make liquid hydrocarbons , suggesting solution to transport problem in the industry.Therefore, we suggest new system to convert methane into liquid products via oxygen reduction reaction using cathode. Recently in some papers, oxygen is used as an oxidant in photocatalytic system to oxidize methane into liquid hydrocarbons. Herein, hydrogen peroxide (H2O2) generated from oxygen reduction reaction can produce hydroxyl radical, superoxide radical, and hydroperoxide radical with strong activity to break first C-H bond from CH4. By combining methyl radical activated from methane and radicals generated from H2O2, we could make formic acid with high selectivity. Through the reduction reaction on cathode and oxidation reaction by radicals, intermediate products, such as methanol and methyl hydroperoxide, were finally converted into formic acid. Furthermore, overoxidation, one of important limitation in direct methane oxidation, can be prevented by using cathode where reduction reaction occurs on electrode.In this work, we synthesized metal organic framework (MOF)-derived cobalt single atom using ZIF-67. The cobalt single atom has high faradaic efficiency (FE) in acidic media with low onset potential, which is over 80% at 0.5 V (vs RHE). To efficiently utilize H2O2 produced by oxygen reduction reaction, additional hydrophobic layer was introduced with gas diffusion electrode (GDE) by coating poly tetra fluoro ethylene (PTFE) on catalyst layer. Additional PTFE layer on GDE confined H2O2 and CH4 together, offering higher possibilities to be reacted. In addition, liquid oxygenates generated from the reaction have hydrophilic properties that prevents further reactions by reducing the diffusion of liquid products toward cathode due to hydrophobic layer. By applying new system into flow cell, the low solubility of methane in the electrolyte can be alleviated to achieve high production rate. At last, This new system using oxygen reduction reaction to oxidize methane can make a new pathway for many chemical reaction area in the point that the system can be applied in any industrial reactions where H2O2 included. Figure 1

Delamination detection on composite laminates using the modal displacement unevenness coefficient

This paper develops a new detection method taking the power function of the modal displacement curvature difference as a damage index to accurately identify the location and degree of the delamination. The 4-layer Poly Tetra Fluoro Ethylene films of size 0.02 m × 0.11 m are embedded between adjacent carbon fiber prepregs being 0.06 m and 0.115 m away from the left edge, respectively. The force-hammer excitation experiment is carried out on the prepared laminates with fixed supports at both ends, and the frequency response curves of measuring points are processed by the Polylscf algorithm in Dong-Hua Data Analysis System. The finite element model of delaminated laminates is established through adding new layers with film properties, and the modal displacements of nodes are compared with experimental data. The number of measuring points in the experiment is limited, making the precise characterization of surface abrupt characteristics difficult. The numerical results are used to calculate the square of the Gaussian curvature difference between the modal displacements of intact and damaged laminates. Significant improvement of the delamination detection accuracy is achieved in this process, confirming that the developed method constitutes a valuable tool for the Non-Destructive Testing of the laminates.