Pure PTFE Research Articles

Enhanced Combustion Properties of Al-Si Eutectic Alloy in Energetic Mixtures

This study investigates the feasibility of using an Al-Si eutectic alloy as a reactive fuel in energetic mixtures. Al-Si eutectic alloy powders were obtained from secondary resources and ground to a particle size of less than 100 μm. We examined these powders’ burning characteristics and thermal properties compared to pure Al powder. Results showed that the burning rate of energetic mixtures containing Al-Si eutectic alloys was 1.5 to 2.0 mm/s higher than those with pure Al. Additionally, the activation energy of pure PTFE was reduced from 81.29 kJ/mol to 61.75 kJ/mol when the Al-Si alloy was added. The formation of oxides, carbides, and fluorides in the combustion products of Al-Si-based mixtures significantly influenced their thermodynamics.

Investigation of Tribological Behavior of PTFE Composites Reinforced with Bronze Particles by Taguchi Method

Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.

High Temperature Friction and Wear Behavior of PTFE/MoS2 Composites

High performance polymer matrix composites with low friction and wear rate are of urgent requirement in sliding bearings and gaskets. In this study, the PTFE/MoS2 composites were prepared and the effect of testing temperature on the tribological properties were investigated. Results show that the friction coefficient and wear rate are approximately (0.14–0.19) and (4.18–13.38 × 10−4 mm3/Nm) at testing temperatures from 25 to 250 °C, respectively. At testing temperatures above 200 °C, the coefficient of friction of the composite with the addition of MoS2 is lower than that of pure PTFE, while the wear rate of the composite material with the addition of 2 wt.% and 5 wt.% MoS2 is lower than that of pure PTFE at temperatures above 150 °C. At low testing temperatures (25–100 °C), the main wear mechanism is that of slight abrasive wear, while from 150 °C to 250 °C, the main wear mechanism transformed to fatigue and severe abrasive wear.

Design and construction of PTFE porous membranes with high modulus and structural stability via in-situ interlocking and anchoring strategy

PTFE nanofiber membrane, as an effective supplement to biaxial stretched PTFE membrane, suffers from low modulus and poor structural stability. In this study, the PTFE porous membrane with high modulus and structural stability was designed and achieved via the in-situ interlocking and anchoring strategy by co-electrospinning polyacrylonitrile (PAN) into PTFE matrix. During the sintering process, the continuous flexible PTFE nanofibers formed, while PAN nanofibers was pre-oxidized to create a stable trapezoidal structure. The effects of pre-oxidized PAN (OPAN) nanofibers' content and diameter on the morphology and structure of the PTFE/OPAN composite nanofiber membrane were investigated in detail. Results showed that the introduction of OPAN nanofiber effectively improve the modulus and structural stability of PTFE nanofiber membrane. The Young's modulus and tensile strength of the composite nanofiber membrane were over 50 MPa and 2 MPa, which were 1166% and 80% higher than that of pure PTFE nanofiber membrane, respectively. These results of this work would contribute to solve the defects of PTFE nanofiber membrane's low modulus and poor structural stability, and then expand its application scope.

Experimental Study on Damage Characteristics of Copper-Reinforced Polytetrafluoroethylene Shaped-Charge Warhead Liner.

Polymer materials have important applications in the4 terminal effect and damage by shaped-charge warheads. However, the low strength of pure PTFE materials reduces the penetrability of the expansive jet from these warheads, hindering its application. This study improves the strength of pure PTFE material by adding Cu powder to the shaped-charge liner. Three types of PTFE/Cu composites with different densities are prepared. The effect of increasing the density on the performance of an expansive jet is studied by a dynamic mechanical property experiment, microscopic analysis, numerical simulation, and a penetration experiment. The results show that the toughness and impact strength of the PTFE/Cu composites improve when 18–50.5% Cu is added. The strength of the composite increases linearly with the increase in Cu content. Numerical simulations and X-ray pulse experiments reveal that the addition of Cu powder enhances the cohesiveness of the head of the expansive jet. The jet head becomes more cohesive as the Cu content is increased. However, the length and diameter of the jet become smaller. The jet can create a deeper hole in the steel target and increase damage as more Cu is added to the liner.

Bifunctional RbBiNb2O7/poly(tetrafluoroethylene) for high-efficiency piezocatalytic hydrogen and hydrogen peroxide production from pure water

Overall water splitting initiated by the green energy is a challenging yet promising route to address the worldwide environmental and energy issues. Herein, we report the implementation and unraveling of the piezoelectric effect of RbBiNb2O7/poly(tetrafluoroethylene) (RBNO/PTFE) on promoting the thermodynamically favorable 2e- reaction to significantly enhance their overall water splitting (i.e., simultaneously producing H2O2 and H2) via piezocatalysis. HRTEM, XPS and FTIR results confirm the successful preparation of RBNO/PTFE. The piezo-responses of RBNO/PTFE are uncovered by PFM. Remarkably, exceptional H2 and H2O2 production rates (i.e., 260.79 and 219.23 μmol g-1h-1, respectively) are achieved over RBNO/PTFE in pure water without cocatalysts upon the ultrasonic excitation, far exceeding those of pure RBNO and PTFE. Specifically, the piezoelectric polarization of PTFE causes the band tilt of RBNO, leading to the energy match between the required redox potential and the band structure of RBNO towards dynamically favorable H2 and ·OH mediated H2O2 generation. In addition, the hydrophobic modification of PTFE over RBNO makes water oxidation reaction occur toward the H2O2 production. Given the diversity of materials possessing the mechanical-force-to-chemical-energy conversion, this work may provide a robust way to underpin future advances in the catalytic renewable-energy production.

Hydrophobicity, water moisture transfer and breathability of PTFE-coated viscose fabrics prepared by electrospraying technology and sintering process

Coating of PTFE on the fabrics is one facial method to obtain the hydrophobic/superhydrophobic property. However, the breathability of the PTFE-coated fabrics prepared by traditional methods (e.g., sputtering) is significantly affected. Electrospraying technology was able to create the pure PTFE coating layer on any substrates and the following sintering process is necessary to obtain the hydrophobic/superhydrophobic property. In this work, the PTFE-coated viscose fabrics were firstly prepared via electrospraying technology and then stabilized after 10 min sintering process with different temperatures ranging from 150 °C to 210 °C. The morphology, hydrophobicity, breathability, and water moisture transfer of the PTFE-coated viscose fabrics as well as the chemical compatibility between PTFE microparticles and viscose fabric were investigated. With increased sintering temperature, the PTFE coating layer on the viscose fabric became physically denser, which corresponded to the reduced breathability. Only when sintering temperature was equal to or higher than 190 °C, the stable hydrophobicity of PTFE-coated viscose fabric was found. When sintering temperature was increased from 190 °C to 210 °C, the contact angle hysteresis of the hydrophobic PTFE-coated viscose fabric decreased from 9.2° to 3.4° and the one-way water moisture transfer was enhanced.

Adhesive-Free Adhesion between Plasma-Treated Glass-Cloth-Containing Polytetrafluoroethylene (GC-PTFE) and Stainless Steel: Comparison between GC-PTFE and Pure PTFE.

In this study, the effect of plasma treatment on glass-cloth-containing polytetrafluoroethylene (GC–PTFE) was investigated. Previous plasma studies investigated pure PTFE (which does not contain glass cloth) but not GC–PTFE. The effect of Ar + H2O plasma treatment on GC–PTFE was investigated. The Ar + H2O plasma-treated GC–PTFE sheets were thermally compressed to stainless steel (SUS304) foils without using adhesive, and the GC–PTFE/SUS304 adhesion strengths were measured using a 90° peel test. The adhesion strength increased with the increase in the plasma treatment time (0.8 and 1.0 N/mm at 20 s and 300 s, respectively). Thus, strong adhesion between GC–PTFE/SUS304 was achieved without adhesive. This improvement in the adhesion properties of GC–PTFE can be attributed to the generation of oxygen-containing functional groups and the decrease in the surface roughness of the samples. Thereafter, the adhesion properties of GC–PTFE and pure PTFE were compared. Because, unlike pure PTFE, GC–PTFE has no weak boundary layer, GC–PTFE exhibited better adhesion properties than pure PTFE under short plasma treatment times.

Adaptation brings increased efficiency

The Lewa M900 is a pump head with a hydraulically actuated diaphragm made of pure PTFE and a diaphragm holder made of stainless steel. Now the company has further developed the pump head, doubling its volumetric efficiency and adapting it for use with the smaller Lewa Ecoflow models.

Wear resistant solid lubricating coatings via compression molding and thermal spraying technologies

This work combines two industrially friendly processing methods in order to create wear resistant and solid-lubricating composite coatings potentially suitable for high load applications. Layered composite coatings were fabricated over wrought stainless steel 444 (SS444) by compression molding a mixture of solid lubricant polymer, polytetrafluoroethylene (PTFE, 80 wt%), and wear resistant polymer, polyimide (PI, 20 wt%), onto iron aluminide (Fe3Al) thermal spray coatings without the need of either primers or adhesives. The fabrication process consisted of three main steps: deposition of the Fe3Al thermal spray coating onto a SS444 substrate and transfer into a metal mold; transfer, compress, and sinter mixed polymeric powder onto the thermal spray coating; and finally, sample cooling to room temperature. This method takes advantage of the high surface roughness of thermal spray coatings, which increases mechanical adhesion of slippery PTFE to the underlying metallic material. Coatings were produced with and without a small amount of graphite (5 wt%) to analyze its impact on sliding and wear properties. Unlike current coating technologies, the thickness of the coatings presented herein can be easily and quickly tailored by varying the amount of polymer powder added to the mold prior to compression or by grinding after fabrication. We produced and analyzed coatings ~1.3 mm in total thickness that portray coefficient of frictions ~0.1, similar to pure PTFE. The calculated wear rates for both coatings with and without graphite are an order of magnitude lower than what has been previously reported for coatings of similar composition. The influence of graphite on wear properties was found to be minimal due to the high content of self-lubricating PTFE yet can act as a way to lower material costs and increase the coatings load capacity.

Novel PTFE/CNT composite nanofiber membranes with enhanced mechanical, crystalline, conductive, and dielectric properties fabricated by emulsion electrospinning and sintering

Polytetrafluoroethylene/multiwalled carbon nanotubes (PTFE/CNT) nanofiber membranes were prepared by emulsion electrospinning and high temperature sintering. Compared with pure PTFE nanofiber membranes, at low CNT content, the mechanical properties of PTFE/CNT nanofiber membranes were improved. For example, the tensile strength of PTFE/CNT (0.5 wt%) composite nanofiber membranes increased from 2.5 MPa to 5.92 MPa, and the elongation at break increased from 123% to 330%. The conductivity of PTFE/CNT (5 wt%) nanofiber membranes reached 1.5 S/m. Meanwhile, the dielectric constant and dielectric loss of PTFE/CNT (5 wt%) nanofiber membranes are 58.46 and 2372.3 respectively. The PTFE/CNT (1 wt%) composite nanofiber membrane displayed an optimal reflection loss of −53.2 dB with a thickness of 2.0 mm. After adding CNT, water contact angle value was slightly reduced from 135° of pure PTFE to 133.55°, but still has good hydrophobicity. What's more, the obtained PTFE/CNT nanofiber membranes also showed good thermal properties and permeability as well as oil absorption characteristics, endowing it many great potential applications, such as electromagnetic wave absorption, electronic packaging, and oil-water separation and so on.

Tribological Behavior of Poly(tetrafluoroethylene) and Its Composites Reinforced by Carbon Nanotubes and Graphene Sheets: Molecular Dynamics Simulation

Low‐dimensional fillers play an important role in improving the tribological properties of poly(tetrafluoroethylene) (PTFE) composites. However, the reinforcement mechanism is not fully understood, since few in situ experiments are able to capture the dynamics evolution and interfacial behavior of fillers. Herein, the tribological behavior of PTFE composites filled with graphene (Gr) sheets and carbon nanotubes (CNT) at the nanoscale is investigated. The results demonstrate that the composites filled with the CNT and Gr fillers have much better wear resistance than that of the pure PTFE, and the wear amounts are reduced by 76.2% and 85.7%, respectively. The relative bond and angle energy of PTFE indicate less deformation in the reinforced composite matrices. The calculations of interfacial interaction energy and radial distribution function reveal that the Gr fillers have better reinforcements than CNT due to stronger interactions at the Gr/PTFE interfaces.

Comparative Study on the Frequency and Wear of Thermoplastic Polymeric Materials Based on PTFE

The widespread use of thermoplastic polymeric materials in various industrial fields has shown considerable interest in understanding the frictional and wear behavior. Among these polymers, polytetrafluoroethylene, also called PTFE, is a high-performance plastic that offers high chemical and thermal resistance and low friction. Additives such as fiberglass, carbon and graphite fillers are added to PTFE to significantly increase thermal conductivity, stiffness and self-lubricating properties. The materials subjected to the experimental analysis were pure PTFE, PTFE + 15% fiberglass, PTFE + carbon-graphite which slipped, under conditions of dry friction, on a sample of non-alloy steel construction SR EN 10025 from 1994. The tests were performed on a pin-on-disc tribometer. The effect of loading and sliding speed on the tribological properties of the polymer / steel combination under dry slip conditions was investigated and the specific wear rate for the experimental conditions was evaluated. The tests were performed at loads of the pin of Fn1=1N, Fn2=3N, Fn3=5N and Fn4=10N and sliding speeds of 1=1m/s, 2=3m/s. The results obtained indicated that the coefficient of friction decreases with increasing load. The wear rate for the analyzed materials was between 10-13...10-15 m2/N, the fiberglass reinforced PTFE material having the lowest wear rate. The present paper, through a comparative analysis of the friction and wear behavior, highlights the effects that the ingredients introduced in the basic material have, under the action of the exploitation factors (loading, sliding speed).

Research on the Effect of Temperature on Tribological Properties of PTFE Composites under Oil Lubrication Conditions

PTFE and its composites are widely used in various reciprocating sealing materials due to their extremely low friction coefficient. As pure PTFE has poor wear resistance at high temperature, it is necessary to study the tribological properties of PTFE with different fillers under the condition of high temperature and oil lubrication. The friction and wear properties of PTFE and PTFE composite material filled with bronze powder, carbon powder, carbon fiber, glass fiber and MoS2 powder were studied by standard friction and wear test using SRV-4 tribotester. Results showed that the wear resistance was all improved indicating that the fillers increased the wear resistance of PTFE, PTFE composite filled with MoS2 has the lowest coefficient at ambient temperature and the highest at high temperature, PTFE composites filled with carbon fiber have the lowest wear rate at all temperatures.

Improved Load-Bearing Capacity and Tribological Properties of PTFE Coatings Induced by Surface Texturing and the Addition of GO

The PTFE coatings with excellent corrosion-resistance and lubrication properties often stop functioning under high load conditions. In this study, a composite coating of PTFE filled with silane coupling agent modified graphene oxide (mGO/PTFE) was prepared by a simple spin-coating process on textured stainless steel (SS) substrate to protect the substrate from failure under high load rubbing. The grafting reaction between GO and silane coupling agent was analyzed by FTIR, Raman, XRD, TGA, and XPS. The morphologies and tribological properties of the mGO/PTFE coatings on the untextured and textured SS substrates were characterized by SEM and UMT tribometer. The results showed that GO surfaces were successfully grafted by silane coupling agent, resulting in that the composite coating of mGO/PTFE was denser than the pure PTFE coating. The tribo-test results confirmed that the groove texture processed by laser surface texture technology greatly improved the load-bearing capacity and anti-wear life of the PTFE coatings. The PTFE coating on the untextured SS surface fails within half an hour of rubbing at the applied load of 10 N, while the one on the groove-textured surface can maintain low and stable friction coefficient for a long time even under the load of 50 N. In addition, the results showed that the loading of mGO further improve the friction reduction and wear resistance of the PTFE coating on the textured SS surface. The wear scar width and the friction coefficient are significantly reduced by 70% and 30%, respectively, as the PTFE coating was filled by 1.0 wt% mGO. Finally, the mechanisms for achieving outstanding properties of the composite coating of mGO/PTFE on the textured SS surface were illustrated by analyzing the wear surfaces of the coating and the counterpart balls by SEM and EDS.

Surface-modified Li3Mg2NbO6 ceramic particles and hexagonal boron nitride sheets filled PTFE composites with high through-plane thermal conductivity and extremely low dielectric loss

Polytetrafluoroethylene has been widely applied in advanced electronic devices due to low dielectric loss and high thermal stability. Nevertheless, its low thermal conductivity can't satisfy heat diffusion demand under the situation of high-frequency and high-speed signal transmission. The PTFE-based composites filled with hybrid fillers of Li3Mg2NbO6 ceramic particles and hexagonal boron nitride sheets modified by phenyltrimethoxysilane were fabricated. Surface modification enhanced the interface compatibility between PTFE and fillers, thus obtaining tight microstructure and better dielectric properties for the composites. The dielectric properties, thermal conductivity, coefficient of thermal expansion and flexure strength of the composites were researched systematically. When the composites were filled with 40 vol% BN sheets and 10 vol% Li3Mg2NbO6 particles, the high through-plane thermal conductivity of 3.3 W·m−1·K−1 was obtained, which was 1220% higher than pure PTFE. Meanwhile, the low dielectric constant of 3.9, extremely low dielectric loss of 3.3 × 10−4 at 9.5 GHz and low coefficient of thermal expansion of 35 ppm/°C were also achieved. PTFE-based composites with high through-plane thermal conductivity and extremely low dielectric loss show huge potential for microwave substrates application.

Adhesion and Interface Properties of Polydopamine and Polytetrafluoroethylene Thin Films

Abstract Polytetrafluoroethylene (PTFE) has been studied as a low friction surface coating since its discovery. The high wear-rate of PTFE reduces the usefulness of the polymer for mechanical purposes; however, combining PTFE with polydopamine (PDA) has been shown to greatly reduce the film wear-rate. During rubbing tests involving PDA/PTFE thin films, a tenacious layer of PTFE remains intact after substantial testing even though pure PTFE film layers are destroyed quickly. Understanding the interface mechanics that allow PTFE and PDA to adhere so well during experimental rubbing tests is necessary to improve the wear-rate of PDA/PTFE thin films. In this study, we use density functional theory (DFT) and molecular dynamics (MD) simulations to investigate the adhesive properties and interface deformation mechanisms between PDA and PTFE molecules. Steered molecular dynamics (SMD) is then performed on isolated pairs of PDA and PTFE molecules to investigate different modes of deformation from equilibrium. PDA trimer oligomers were identified as the most adhesive to PTFE and selected to use in a PDA/PTFE thin film, where nano-indentation and scratch tests are performed. Our results indicate that a combination of the unique deformation mechanisms of PDA molecules and the penetration of PTFE molecules into the PDA substrate provide the PTFE/PDA interface with its wear resistance.

Synthesis of surface modified hydrophobic PTFE-ZnO electrospun nanofibrous mats for removal of volatile organic compounds (VOCs) from air

The article reports a two-step synthesis of composite nanofibrous mats of polytetraflouroethylene/zinc oxide (PTFE-ZnO); first, emulsion electrospinning of precursor solution was performed to yield as-spun mats followed by heat treatment at 280 °C. The surface of pure PTFE nanofibrous mats was modified by varying the amount of ZnO loadings in the electrospinning solution from 10 to 20 wt.%. Physiochemical characterization of synthesized mats was performed by FESEM, EDX, AFM, FTIR, Raman, TGA and contact angle goniometry. It was observed that fiber mean diameter decreased from 0.243 ± 15.10 μm to 0.17 ± 30.50 μm, RMS roughness increased from 112 to 627 nm and CA improved from 102.56° to 121.55° with the rise in ZnO content up to 20 wt% compared to the pure PTFE mats. Higher surface area, roughness and hydrophobicity of PTFE-ZnO mats resulted into significantly enhanced adsorption ability of VOCs on their surfaces against three model VOCs, namely, toluene, acetone and formaldehyde. The results have demonstrated that surface adsorption capacity of tested VOCs has considerably increased to 10, 07 and 03 folds respectively for the nanofibrous mats containing 20 wt.% ZnO, compared to pure PTFE mats. Based on these findings, these nanofibrous mats can potentially be used as filters for VOCs and particulate removal from air in the processing industries.

Effect of Graphite and Bronze Fillers on PTFE Tribological Behavior: A Commercial Materials Evaluation

This work presents a tribological evaluation of the influence of graphite and bronze fillers in two commercial composites in a dry sliding pin-on-disc test at the same contact severity ( parameter) and four testing conditions (varying both normal force and sliding velocity). Both fillers, in comparison to pure PTFE, significantly affected the coefficient of friction (COF) and the mass loss. The sliding distance required to reach steady-state for COF was statistically equal for all three materials. The COF experienced a relevant influence of both normal force and sliding velocity. The graphite filler acted as a solid lubricant and exhibited reductions in COF (∼27% on average) and in mass loss (∼4.2 times lower on average). The bronze filler, on the other hand, had a COF increase of up to 5% for conditions with lower normal force but showed a significant reduction on the specific mass loss (∼5.3 times lower on average). Due to its higher thermal conductivity, the composite filled with graphite presented lower tribosystem temperatures in thermography evaluations. Good agreement of the temperature data was found considering a model that proposes the rate of heat generated by friction. With respect to wear of the composites, evidence of adhesion (transfer films to the counterface) and abrasive (microploughing and microcutting) wear mechanisms was found, in addition to the identification of preferential wear.

Core-shell polytetrafluoroethylene @ phenolic resin composites: Structure and tribological behaviors

Abstract Polytetrafluoroethylene @ phenolic resin (PTFE@PR) core-shell particles were successfully synthesized through a versatile one-pot method, which were investigated in tribological characteristics. The core-shell structure was characterized by transmission electron microscopy (TEM), fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). The results demonstrated that core-shell composites possess the lower friction coefficient and better anti-wear performance. Friction coefficient of the composite is about 0.178 as low as pure PTFE at 50 N and 0.033 m/s. Meanwhile, the wear volume of the composite was measured at 0.59 mm3 by rubbing 1 h, which is merely a fifteenth of pure PTFE (8.94 mm3). The chemical action of core-shell composites resulted in the uniform and integrate transfer film, so that outstanding tribological performances of core-shell composites were exhibited.