PTFE Matrix Research Articles

Mechanical Property Improvement of Carbon Fiber-Reinforced PTFE Composites by PA6 Filler Dispersion

Mechanical properties of carbon fiber reinforced composites and polyamide6 (PA6) particles dispersed carbon fiber hybrid-reinforced composites were investigated. Mechanical properties were improved by incorporating PA6 particles into the PTFE matrix. Hybridization effects on the mechanical properties of carbon fiber reinforced-PTFE composites with PA6 particles are discussed. In the present experiment, an attempt has been taken to disperse PA6 particles into carbon fiber-reinforced composites (CFRP) matrix to fabricate carbon fiber-reinforced hybrid composites (CFHRP). The main purpose of hybridization is to optimize the properties of the matrix for high performance fiber-reinforced composites.

Polytetrafluoroethylene modification by radiation grafting of vinylidene chloride and its dehydrochlorination

A process has been designed for manufacturing a new composite material consisting of a PTFE matrix with a carbon phase implanted in the surface layer of up to 30 μm thickness. The process involves radiation graft polymerization of vinilydene chloride (VDC) from the vapor phase onto the PTFE matrix followed by dehydrochlorination of implanted PVDC. The VDC grafting kinetics, the distribution of the grafted polymer and the carbon phase, and the mechanical characteristics of the composite material have been investigated. It has been shown that unlike initial PTFE, the composite possesses good adhesive bonding properties and a small contact angle.

Microstructure of PTFE-Based Polymer Blends and Their Tribological Behaviors Under Aqueous Environment

Four polytetrafluoroethylene-based polymer blends (PTFE blends) with polyimide (PI), polyether ether ketone (PEEK), poly(phenyl p-hydroxybenzoate) (PHBA), and perfluoroethylene propylene copolymer (FEP) were prepared by compression molding and follow-up sintering. Their microstructure was observed by scanning electron microscope. And the tribological behaviors of PTFE blends sliding against 316 steel under pure water and sea water lubrication were comparatively evaluated using block-on-ring tribology test rig. The worn surface of counterpart was examined by X-ray photoelectron spectroscopy. The results showed that by blending with the four polymers, PTFE exhibited the transformed microstructure and improved wear resistance. Compared with FEP, rigid polymers PI, PHBA, and PEEK can enhance the wear resistance of PTFE greatly because they can effectively improve the load-carrying capacity of PTFE matrix and can more efficiently prevent the crystalline bands of PTFE from being pulled out. However, because of the weak inhibition on the pulling out of PTFE crystalline bands, FEP cannot enhance the wear resistance of PTFE as significantly as other polymers. In addition, the friction coefficients and wear rates of PTFE and its blends were lower under the lubrication of sea water than under the lubrication of pure water, which was ascribed to more excellent lubricating effect of sea water originating from the deposition of CaCO3 and Mg(OH)2 onto the sliding surfaces.

Simulation of tribological functionality of heterogeneous tribomaterials

We simulated the tribological functionality of two heterogeneous tribomaterials used in conformal contacts by means of a FEM-based approach: journal bearing material AlSn20 and polymeric sealing material PTFE with bronze filler particles. For AlSn20, the emergency running capability, which is based on the activation (melting) of the soft phase tin, was simulated taking into account thermo-elasto-plastic behaviour of the material. For the PTFE bronze compound, we analysed the load bearing capacity of the particle-structured surface with varying volumetric fraction of particles, temperature, load and creep behaviour of the PTFE Matrix. The results show benefit of heterogeneous designs over homogeneous materials.

Structural characterization and high-temperature compressive creep of PTFE-based composites filled with inorganic nanoparticles

The PTFE-based nanocomposites with various contents of inorganic nanoparticles (n-AlN and n-Si3N4) were prepared by cold compaction followed by free sintering. The results of scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction show that PTFE spherulite formed in the nanocomposites. When 2 wt% inorganic nanoparticles were added into the PTFE matrix, the crystallinity increased from 34.3% to 42.1% and 43.2%, respectively. Moreover, the interplanar distances for each crystal plane were enlarged and the grain sizes were smaller than that of pure PTFE. In addition, the mechanical and high-temperature compressive creep properties were investigated. The results indicate that the introduction of inorganic nanoparticles largely increased the high-temperature compressive creep resistance, and the maximal reduction of percentage of creep strain was up to 68%. The tensile strengths of the nanocomposites increased with increasing filler content when it was no more than 2%, and then decreased with the further increase of the filler content, whereas the elongations at break showed a reverse tendency. Copyright © 2011 John Wiley & Sons, Ltd.

A Fluoropolymer Coating on Carbon Fibers Improves Their Adhesive Interaction with PTFE Matrix

Carbon fibers were treated in a HF glow discharge in tetrafluoroethylene and octafluorocyclobutane in order to improve their adhesion to poly(tetrafluoroethylene) matrix. As the result of the plasma treatment, a thin (20–140 nm) fluoropolymer coating was deposited onto the fiber surface. The structure of this coating was studied by means of IR spectroscopy, XPS, AFM and SEM techniques. The coating material appeared to be similar to PTFE in its chemical composition but distinguished by branched, partially crosslinked, amorphous structure and included unsaturated chemical bonds. The coating thickness of 70 nm was sufficient to effectively screen the field of molecular forces of the initial substrate, thus, decreasing the surface energy of the fibers and improving their compatibility with the PTFE matrix. The adhesive strength in the PTFE–carbon fiber systems, measured by means of the microbond test, more than doubled upon the plasma treatment (the local interfacial shear strength increased from 10.7 to 29.7 MPa, apparent IFSS from 4.3 to 7.8 MPa), and the interfacial frictional stress increased by 70%. The new composite material consisting of 20% short coated carbon fibers in the PTFE matrix showed better mechanical, thermal and tribological characteristics as compared with the composite reinforced with untreated fibers.

Mechanical Characterization of Silica Reinforced-PTFE Matrix Composites

Most of the currently available technologies require the use of materials with unusual combinations of properties that cannot be met by metallic alloys, ceramic or conventional polymeric materials. Polymer composites are designed to meet the requirements and challenges of industry, where there is an increasingly growing demand for special materials, involving the best cost-benefit relationship. The main objective of this work is to characterize a poly(tetrafluoroethylene) (PTFE) matrix reinforced with silica particles. The approached used consisted in investigating the macroscopic mechanical behavior and correlating the experimental results with a suitable viscoelastic analytical model. Moreover, to assess the influence of the particles on the viscosity, stiffness and strength of the composite, the behavior of the PTFE-silica composite is compared with the behavior of the bare PTFE matrix.

Effects of Accelerated Ageing in a PTFE Matrix Polymer Composite

AbstractThe objective of this work is to present a comparative study of the behaviour of a polymer composite before and after accelerated ageing with exposure to UVB radiation and water vapour. The goal is to propose a methodology to characterise material ageing by observing its phenomenological behaviour without taking into account chemical or physical changes that result from ageing. With this objective, tensile and creep tests were performed and the experimental results were used in an inverse approach to identify the material parameters in a three‐parameter rheological model. A silica‐polytetrafluoroethylene (PTFE) matrix reinforced composite was investigated. It was verified that significant differences in the composite behaviour only occurred after a long time. In particular, the strength of the composite increased significantly.

Effect of Particle Size on the Microwave Dielectric Properties of Alumina‐Filled PTFE Substrates

α‐alumina of different particle sizes of 50 nm, 0.4, 3, and 7 μm have been incorporated into the PTFE matrix to prepare flexible composite substrates. A proprietary process comprising of sigma mixing, extrusion, and calendering, followed by hot pressing (SMECH process) has been used to obtain dimensionally stable ceramic‐filled PTFE substrates. Variation of the dielectric constant, loss tangent and moisture absorption of filled PTFE composites has been ascertained as a result of filler loading.

Effects of silane coatings in aqueous and non-aqueous media on the properties of magnesia filled PTFE laminates

Silane coated on magnesia particulates in isopropyl alcohol (IPA) medium, precluded the formation of brucite phase, which hitherto existed in silane coated on magnesia filler in aqueous medium. Both the types of coated MgO powders were separately filled in the PTFE matrix, and microwave flexible substrates were made by the process comprising of sigma mixing, extrusion, calendering and hot pressing (SMECH process). Filler content in the PTFE matrix was varied from 10 to 70 wt% and microstructures of the composites were analyzed using SEM technique. The dielectric properties of the planar substrates were measured at X-band using waveguide cavity perturbation technique. The IPC-TM-650 procedure was employed to evaluate the moisture absorption characteristics.

PTFE based composite anion exchange membranes: thermally induced in situ polymerization and direct hydrazine hydrate fuel cell application

Anion exchange membrane fuel cells (AEMFCs) are advantageous over proton exchange membrane fuel cells in terms of electrode reaction kinetics and electrocatalyst versatility. As one of the key materials for this type of fuel cell, AEM transports anions from cathode to anode during cell operation and governs the performance of AEMFC. In this work, we report on the fabrication of a novel type of PTFE based composite anion exchange membrane and its application in direct hydrazine hydrate fuel cells (DHFC). The membrane was prepared viain situ thermal polymerization of chloromethyl monomer in pre-treated PTFE matrix followed by quaternary amination and alkalization. Attributed to a high chloromethyl monomer uptake and a membrane structure featuring “hydrophobic matrix confined hydrophilic domain”, the fabricated membrane showed hydroxide conductivity up to 0.049 S cm−1 at room temperature and a maximum DHFC power density of 110 mW cm−2 at a voltage of 0.7 V. Such membranes are promising candidates for application in AEMFC.

Influence of serpentine content on tribological behaviors of PTFE/serpentine composite under dry sliding condition

Abstract This paper presents a PTFE/serpentine solid lubricant composite that exhibits low friction coefficient and low wear rate. It is postulated that synergistic effect alters the dominant wear mechanism of PTFE matrix. In order to examine the influence of serpentine content on tribological properties of PTFE/serpentine composite, six blends of PTFE with serpentine (in the range of 0–30 wt.%) were evaluated using a MMU-5G friction and wear tester. Tests were carried out in standard laboratory conditions with a nominal contact pressure of 2.85 MPa and a sliding speed of 0.48 m/s. The friction coefficient of the composite, which was weakly dependent on serpentine content, was stable roughly from μ = 0.10 to 0.12 during steady friction. Compared with the wear rate of unfilled PTFE, the wear resistance of PTFE/serpentine composite increased 24 times. However, the content of serpentine (5–30 wt.%) had little effect on wear rate of composite. The images of confocal laser scanning microscope (CLSM) revealed that the hybrid transfer film generated on the surface of mating pair is likely responsible for the lower wear rate obtained in these experiments.

Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment

A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133 ± 3° to 30 ± 4° treated at 100 °C for 3 h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65–0.10 treated by the mixture at 100 °C for 3 h. Hydrophilic groups such as carbonyl (C O) and hydroxyl ( OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K 0.27MnO 2·0.54H 2O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.

Hydrophilic treatment poly(tetrafluoroethylene) reinforced sulfonated poly(ether ether ketone) composite membrane for proton exchange membrane fuel cell application

A reinforced composite membrane based on SPEEK (sulfonated poly ether ether ketone) and porous PTFE substrate (polytetrafluoroethylene) is fabricated and investigated for proton exchange membrane fuel cell application. In order to improve the combination between SPEEK polymer and PTFE matrix, PTFE substrate is hydrophilically pretreated by naphthalene sodium solution. The experimental results indicate that SPEEK can impregnate into treated PTFE substrate (abbreviated as trPTFE) more easily. The variation of PTFE surface property before and after treatment is characterized by water contact angle experiment and ATR-FTIR technique. The impregnated status of SPEEK polymer in PTFE matrix is also characterized by ATR-FTIR. According to the appearance photo of two composite membranes, it is showed that SPEEK/trPTFE composite membrane has more uniform and homogeneous morphology. Moreover, the mechanical property of SPEEK/trPTFE composite membrane also has an advantage over pristine SPEEK membrane. Due to the reinforced effect of trPTFE substrate, thinner composite membrane can be applied in single cell evolution and achieves better performance as a result.

Preparation and properties of silica filled PTFE flexible laminates for microwave circuit applications

Micron and nano size silica fillers are incorporated in the PTFE matrix to prepare flexible composite substrates. A proprietary process comprising of sigma mixing, extrusion, calendering followed by hot pressing (SMECH process) has been employed to obtain nearly isotropic and dimensionally stable filled PTFE substrates. Theoretical modeling has been employed to predict the effective dielectric constant of the composite system and validated the results with experimental data. The distribution of particulate filler in the PTFE matrix has been studied using scanning electron microscopy. The linear coefficient of thermal expansion and ultimate tensile strength of the composite systems with respect to filler loading have been found out. Dielectric properties of the composite substrates at X-band frequency (8.2–12.4 GHz) are measured using waveguide cavity perturbation technique. Moisture absorption of fused silica filled substrates is found out conforming to IPC-TM-650 2.6.2.

Preparation and characterization of cordierite filled PTFE laminates for microwave substrate applications

Phase pure cordierite (2MgO · 2Al2O3 · 5SiO2) powder was prepared through solid state ceramic route. Silane coated cordierite powder was filled in the PTFE matrix through SMECH process comprising of sigma mixing, extrusion, calendering, followed by hot pressing, to fabricate flexible microwave substrates. Filling fraction of cordierite in the PTFE matrix was varied from 10 to 70 wt% and its effects on density, dielectric properties, coefficient of thermal expansion and water absorption were investigated. The morphology and filler distribution of the filled composite were studied by SEM. Waveguide cavity perturbation technique was employed to measure the dielectric properties of the composites at X-band (8.2–12.4 GHz). Dielectric constant and loss tangent were found increasing with filler loading from 10 wt% (er′ = 2.17, tan δ = 0.0007) to 60 wt% (er′ = 3.17, tan δ = 0.0034).

A mechanical durability comparison of various perfluocarbon proton exchange membranes

AbstractMechanical endurance and degradation mechanism of Nafion211 proton exchange membrane and ePTFE/PFSA composite PEMs were investigated in this article. It was found that the shrinkage stress caused by the water‐uptake is the primary source to induce the mechanical decay. The Nafion 211 is more stable when cycle‐stress is lower than 1.5 MPa, while the water‐uptake generating stress can reach to 2.23 MPa soaked in surroundings with condition of 25% RH and temperature at 25°C. The study also found that the ePTFE/PFSA composite PEMs are more durable than the Nafion membrane mostly due to the lower water‐uptake generating shrinkage stress of 0.34–0.4 MPa (25% RH@ 25°C) but not the high yield strength or breaking strength. The PFSA/ePTFE composite membranes can keep stable for more than 5000 cycles, which is about 40% higher than that of the pure Nafion membrane (about 3500 cycles.). For preparing durable proton exchange membrane, it is necessary to improve the proton exchange resin impregnation in the ePTFE matrix. Chemical bonding of the PTFE and the PSFI by modification of the PTFE matrix is also very effective to enhance the mechanical durability of the composite PEMs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Electromagnetic Property of MnZn Ferrite/SrTiO<sub>3</sub>/PTFE Composites

MnZn ferrite powder was modified by SrTiO3 sol and then filled into PTFE matrix to form MnZn ferrite/SrTiO3/PTFE composite. The effect of modification and heat-treatment on the electromagnetic property of the composite was investigated. The results revealed that the as-prepared composite possessed high permeability, high permittivity and low loss. The modification and heat-treatment could improve the electromagnetic property of the composites. The frequency dependence of the dielectric property of the composite is accorded with Debye relaxation theory.

Salicylic acid and derivatives anchored on poly(styrene- co-divinylbenzene) resin and membrane via a diazo bridge: Synthesis, characterisation and application to metal extraction

New materials for chelating solid-phase extraction have been prepared by grafting of salicylic acid and derivatives on poly(styrene- co-divinylbenzene) based sorbents. These sorbents are either resin bead-shaped Amberlite ® XAD-4 or membrane disk-shaped Empore™ SDB-XC. Grafting has been achieved via –N N– spacer. The grafted ligands are salicylic acid (SA), its dimer form methylenedisalicylic acid (MDSA) and trimer form aurintricarboxylic form (ATA) in order to study the influence of multi-functionalization on chelating properties. Grafting scheme was validated on a model molecule (4-ethylaniline) for optimisation of experimental conditions. The resulting sorbents have been characterised by FTIR, Py-GC/MS analysis and 13 C CP-MAS NMR. Grafting rates are higher for SA (25–38%) than for MDSA (16–17%) and ATA (9%), still the number of SA entities remains almost constant. Metallic sorption abilities of the two new sorbents – determined by ICP-AES – have been succcessfully assessed by means of flow-through experiments with synthetic solution of multielement cations (Cd 2+, Co 2+, Cu 2+, Mn 2+, Ni 2+, Pb 2+, Zn 2+, Fe 2+ and Al 3+). It evidenced the influence of the PTFE matrix, contained in Empore disks, for acidic pH. Finally, complexing capacities for Fe(III) were found to be higher for membranes (13.4 ± 0.7 for SA) than for resins (11.6 ± 0.6): this allows to consider grafted polymer membranes as competitive materials for SPE applications.

Fabrication and characterization of improved PFSA/ePTFE composite polymer electrolyte membranes

Capillary analogical experiments have been designed to simulate the impregnation of surfactant-contained Nafion ® solution in porous PTFE (ePTFE) matrix. It is found that the gas pressure in the capillary (initial P inner) is the most important factor for the solution impregnation although the capillary force has slight influence on the capillary rise. The Nafion ® solution can occupy 98.2% (4.91 cm vs. 5 cm) of the end-sealed capillary when the P inner is lowered to 5 × 10 2 Pa. Hence, the decrease of the gas pressure in the porous PTFE matrix is very important to obtain compact Nafion ®/ePTFE composite proton exchange membranes. The PFSA/ePTFE polymer electrolyte membranes (PEMs) prepared in the conditions of initial P inner of 5 × 10 2 Pa and 5 vol.% surfactant concentration are well impregnated and show a high resistance to the hydrogen gas permeability over 4500 dry/wet cycles, indicating a better durability and stability. These thinner and highly conductive composite membranes are significant to improve the fuel cell output voltage. The single cell with the PEM prepared at optimized conditions gives the open circuit voltages of 0.954 V and current density of 1 A cm −2 @ 0.6 V at 60 °C.