Filled Polytetrafluoroethylene Composites Research Articles

Study on the nanoindentation of polytetrafluoroethylene filled with knitted graphene by MD simulations

Knitted graphene with excellent mechanical properties was employed to reinforce polytetrafluoroethylene (PTFE) and their nanoindentation properties were investigated by molecular dynamics simulation. Importantly, the performance of pure PTFE, monolayer graphene (GR) and knitted graphene (KGR) filled PTFE composites were compared based on the extracted morphology, stress and energy to reveal the indentation resistance mechanism of modified materials. The effect of loading depth and environment temperature on nanoindentation was also considered. The simulated results indicated that the indentation resistance of KGR/PTFE composite was superior to others because knitted graphene was able to withstand greater external loads than monolayer graphene. The fundamental reason was that the adsorption effect of KGR on the PTFE chains made their composite carry more external force. Both loading depth and ambient temperature also affected the indentation resistance performance, but loading depth had a greater impact than temperature. The inherent mechanism was explored from interaction potential energy.

Optimization and prediction of tribological behaviour of filled polytetrafluoroethylene composites using Taguchi Deng and hybrid support vector regression models

This study presents optimization and prediction of tribological behaviour of filled polytetrafluoroethylene (PTFE) composites using hybrid Taguchi and support vector regression (SVR) models. To achieve the optimization, Taguchi Deng was employed considering multiple responses and process parameters relevant to the tribological behaviour. Coefficient of friction (µ) and specific wear rate (Ks) were measured using pin-on-disc tribometer. In this study, load, grit size, distance and speed were the process parameters. An L27 orthogonal array was applied for the Taguchi experimental design. A set of optimal parameters were obtained using the Deng approach for multiple responses of µ and KS. Analysis of variance was performed to study the effect of individual parameters on the multiple responses. To predict µ and Ks, SVR was coupled with novel Harris Hawks’ optimization (HHO) and swarm particle optimization (PSO) forming SVR-HHO and SVR-PSO models respectively, were employed. Four model evaluation metrics were used to appraise the prediction accuracy of the models. Validation results revealed enhancement under optimal test conditions. Hybrid SVR models indicated superior prediction accuracy to single SVR model. Furthermore, SVR-HHO outperformed SVR-PSO model. It was found that Taguchi Deng, SVR-PSO and SVR-HHO models led to optimization and prediction with low cost and superior accuracy.

Study on the reinforcing effect of nano-SiO2 filled PTFE composites

The wear behavior and coefficient of friction for Nano-SiO2 filled polytetrafluoroethylene (PTFE) was investigated under dry conditions. The ball indentation hardness, tensile strength and elongation at break were determined. It was found that both ball indentation hardness and tensile properties were better reinforced by nano-SiO2 particles. The tribological properties of the nano-SiO2 PTFE composite and the regular SiO2 PTFE composite were compared for several applied loads. The worn surfaces were examined by means of scanning electron microscopy (SEM) and 3D profilometry. It was determined that the wear rate of PTFE composites filled with Nano-SiO2 particles considerably decreased. The friction forces were found to be lower for the Nano-SiO2 filled composites than those in the regular particles composite for the same experimental conditions.

Fabrication of 0.8BaTi4O9-0.2BaZn2Ti4O11 filled and glassfiber reinforced polytetrafluoroethylene composites with near-zero temperature coefficient of dielectric constant

A study on 0.8BaTi4O9-0.2BaZn2Ti4O11 (BZT) filled and glassfiber (GF) reinforced polytetrafluoroethylene (PTFE) was described. The content of GF was 4 wt. %, and the BZT content varied from 26 wt. % to 66 wt. %. BZT complex phase powder was prepared by one synthetic route and modified using perfluorooctyltriethoxysilane (F8261). The microstructure, thermal properties, dielectric properties and temperature coefficient of dielectric constant of the composites were investigated in detail. The results revealed that BZT/GF/PTFE composites hold outstanding dielectric properties and stable thermal properties. Moreover, the specimens exhibited strong hydrophobicity due to the modification of filler using F8261. The BZT/GF filled PTFE composites exhibited reliable dielectric constant (εr = 4.4), acceptable dielectric loss (tan δ = 0.001), low water absorption (0.02%) and a near-zero temperature coefficient of dielectric constant (τε = 1.57 ppm/°C) at filler with contents of 4 wt. % GF and 46 wt. % BZT.

Evaluation of surface treatment on Li2Mg3SnO6 ceramic powders and the application of Li2Mg3SnO6 powders filled polytetrafluoroethylene composites

In this paper, we studied the properties of polytetrafluoroethylene (PTFE) based and Li2Mg3SnO6 (LMS) filled composites. The LMS powders were synthesized by one synthetic process and modified by C14H19F13O3Si (F8261). The content of modified LMS changed from 26 to 66 wt%. XRD and TEM were employed to investigate the crystal phase of obtained LMS. The analysis of XPS and Contact Angle were conducted to study the surface characteristics of F8261 modified LMS. The morphology, microstructure, dielectric properties of PTFE based composites filled with untreated LMS and modified LMS were investigated in detail. Further, various theoretical models were put forward to discuss the dielectric constant of the composites. At last, the modified LMS filled PTFE composites exhibited reliable dielectric constant (εr = 3.61), acceptable dielectric loss (tan δ = 0.002), stable frequency dependence of dielectric constant and low temperature coefficient of dielectric constant (τε = 9.42 ppm/°C) at filler loading of 46 wt% LMS.

Novel high dielectric constant and low loss PTFE/CNT composites

Spherical Ca0.55Nd0.3TiO3 ceramic filled polytetrafluoroethylene composites (abbreviated as PTFE/CNT) with different filler volume fractions were prepared. The effects of filler volume fraction on microstructure, dielectric properties and thermal property were studied by scanning electron microscope, vector network analyzer and thermal dilatometer, respectively. The SEM results show that spherical particles are advantageous to reduce the porosity in the interphase which would increase the dielectric loss. Moreover, both the dielectric constant and dielectric loss increased with the increasing volume fraction of CNT microspheres. The high dielectric constant and low dielectric loss composite can be prepared when the ceramic volume fraction is 50 V%: εr = 12, tan δ = 8.5 × 10−4 (at 10 GHz). Different models were used to predict the dielectric constant of composite, and the effective medium theory shows the least deviation from the experiment. The experimental coefficient of thermal expansions of composites with different volume fractions were less than theoretical data due to the change from loosely bound polymer chain to tightly bound polymer chain which would restrain the coefficient of thermal expansions of composites.

Microstructure and microwave dielectric properties of Na1/2Sm1/2TiO3 filled PTFE, an environmental friendly composites

A study on Na1/2Sm1/2TiO3 filled and glassfiber reinforced polytetrafluoroethylene (PTFE) composites was described. The GF content was a fixed value of 4 wt%, and the NST content in the composite matrix changed from 26 to 66 wt%. The paper consisted of the manufactural process of the composite and the effects of filler content on the properties of the substrate, such as morphology, moisture absorption, density, dielectric properties and temperature coefficient of dielectric constant. As NST filler loading increased from 26 to 66 wt%, the dielectric constant and loss tangent experienced a continuously increase while the development in τε was opposite. X-Ray Diffraction, FTIR and XPS were used to analyze the microstructure of modified ceramic powder. It was proved that the silane coupling agent has been grafted on the NST surface successfully. At last, the NST/GF filled PTFE composites exhibited good dielectric constant (εr = 4.95), low dielectric loss (tan δ = 0.00147), acceptable water absorption (0.036) and temperature coefficient of dielectric constant (τε = −164) at filler loading of 4 wt% GF and 46 wt% NST.

Effects of perfluorooctyltriethoxysilane coupling agent on the properties of silica filled PTFE composites

Fused amorphous SiO2 filled polytetrafluoroethylene (PTFE) microwave substrate composites were manufactured. The composition of all the samples was 57 wt% SiO2 and 43 wt% PTFE. The effects of compound silane coupling agents on the properties of the SiO2 filled PTFE composites were investigated, including density, water absorption, dielectric properties and temperature coefficient of dielectric constant. Compound coupling agents x wt% KH550+ (1.5−x) wt% F8261 (x: mass ratio to SiO2 ceramic, x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were used to pre-treat SiO2 fillers and the performance of composites were improved with appropriate amounts of coupling agents. The SEM results show that SiO2 particles modified with compound coupling agents are well dispersed in PTFE polymer and exhibit a strong connection with PTFE. The dielectric constant of all the composites shows excellent frequency stability within the frequency from 1 to 18 GHz. The SiO2 ceramic filler modified with 1.1 wt% F8261 and 0.4 wt% KH550 simultaneously has the highest contact angle and the lowest surface energy, besides, the composite achieves a most compact structure with a maximum density of 2.059 g/cm3. At the same time, this composite obtains optimal properties, including good dielectric properties (e r ~ 2.89, tanδ ~ 0.0007), acceptable water absorption of 0.2%, temperature coefficient of dielectric constant (τ e ) of 32.32 ppm/°C. Moreover, the ratio of experimental and theoretical dielectric constant can achieve 98.86%, which is far greater than that in previous reports.

Effects of Content of Chopped Glass Fibers on the Properties of Silica Filled PTFE Composites

In this work, the polytetrafluoroethylene (PTFE)-based composite substrates were manufactured by mixing, calendering, hot-pressing sintering. The composition of all the samples was PTFE, SiO2 and chopped E-glass fibers. The effects of content of E-glass fibers on the properties of the SiO2 filled PTFE composites were investigated, including density, water absorption, dielectric properties (er, tanδ), coefficient of thermal expansion (CTE) and temperature coefficient of dielectric constant (τe). The compositions of inorganic materials mixture are (62 ? x) % SiO2 + x % E-glass fiber (x: mass ratio to composites, x = 0, 1, 1.5, 2, 2.5, 3). The results show that as the content of E-glass fibers is 2.5 wt.%, this composite obtains optimal properties, including excellent dielectric properties (er~2.9123, tanδ~0.0011), acceptable water absorption of 0.075%, temperature coefficient of dielectric constant of 10 ppm/?C and coefficient of thermal expansion of 15.87 ppm/?C.

Effect of irradiation on interfacial interaction and structure formation in filled PTFE composites

The supramolecular structure and tribological properties of filled polytetrafluoroethylene composites irradiated above the melting point of the crystalline phase of the polymer component and the phase transitions in them are investigated. In unirradiated composites, phase separation is observed, that is, the separation of the filler from the polymer matrix. The supramolecular structure of the polymer component does not depend on the nature and concentration of the filler, and it is characterized by the formation of lamellae during sintering and subsequent crystallization. Radiation exposure leads to the disappearance of the phase separation and the formation of axiolites with the radial orientation of fibrils, in the center of which the filler particles are located. Changes in the structure are explained by an increase in interfacial interactions through the radiation grafting of macromolecules (and low-molecular-weight products) to the surface of the filler particles. The linear wear rate of irradiated composites is 50 times lower relative to the unirradiated samples because of the transition from the delamination to abrasive wear mechanism.

Effect of sintering temperature on the crystallization behavior and properties of silica filled PTFE composites

The present study investigated the effect of sintering temperature on the crystallization behavior of polytetrafluoroethylene (PTFE) polymer in SiO2 filled PTFE (PTFE/SiO2) composites, as well as the dependences of dielectric properties, thermal conductivity, water absorption and density on the sintering temperature of composites. The composites were sintered by hot pressing at temperatures of 350–390 °C. The melting peaks of the sintered composites were recorded by the differential scanning calorimetry (DSC), and heats of melting were calculated from the peak areas in DSC curves, then the crystallinity of PTFE in composites was deduced. The intensities of the crystal diffraction peak for PTFE were observed by X-ray diffraction analysis. Moisture absorption of the composites was measured conforming to IPC-TM-650 2.6.2. Archimedes’ principle was used to find out the density of the composites. The dielectric constant and loss tangent of the composites were evaluated at microwave frequency region using strip line resonator method according to IPC-TM-650 2.5.5.5 specification. Thermal conductivity was measured by laser thermal conductivity meter. Morphology of PTFE crystals and dispersion of fillers in the PTFE matrix were studied using scanning electron microscopy.

TiO2 and SiO2 filled PTFE composites for microwave substrate applications

TiO2 and SiO2 filled polytetrafluoroethylene (PTFE) composite substrates were fabricated for microwave circuit applications. The total content of TiO2 and SiO2 fillers was a fixed value of 55 wt%, and the content of TiO2 in the PTFE matrix varied from 1 wt% to 9 wt%. The influences of TiO2 filler loading on the microstructure, density, moisture absorption, microwave dielectric properties and coefficient of thermal expansion of filled PTFE composites were investigated. The distribution of filler was uniform throughout the PTFE matrix. The dielectric constant (e r) showed an increasing trend as the TiO2 content increased, while the dielectric loss (tanδ) decreased up to 5 wt% TiO2 filler loading and then slightly increased till 9 wt% TiO2 loading. Composites showed a similar trend of decreasing moisture absorption, and increasing linear coefficient of thermal expansion (CTE), density as the TiO2 filler content increased. Our results revealed that the TiO2 and SiO2 filled PTFE composites exhibited good dielectric properties (e r ~ 2.87, tanδ ~ 0.00075), acceptable moisture absorption (0.2 %), CTE (17 ppm/°C) and tensile strength (7.32 MPa) at filler loading of 5 wt% TiO2 and 50 wt% SiO2.

Dynamic Mechanical Analysis and Three-Body Abrasive Wear Behaviour of Thermoplastic Copolyester Elastomer Composites

Various amounts of short fibers (glass and carbon) and particulate fillers like polytetrafluoroethylene (PTFE), silicon carbide (SiC), and alumina (Al2O3) were systematically introduced into the thermoplastic copolyester elastomer (TCE) matrix for reinforcement purpose. The mechanical properties such as storage modulus, loss modulus, and Tanδby dynamic mechanical analysis (DMA) and three-body abrasive wear performance on a dry sand rubber wheel abrasion tester have been investigated. For abrasive wear study, the experiments were planned according toL27orthogonal array by considering three factors and three levels. The complex moduli for TCE hybrid composites were pushed to a higher level relative to the TCE filled PTFE composite. At lower temperatures (in the glassy region), the storage modulus increases with increase in wt.% of reinforcement (fiber + fillers) and the value is maximum for the composite with 40 wt.% reinforcement. The loss modulus and damping peaks were also found to be higher by the incorporation of SiC and Al2O3microfillers. The routine abrasive wear test results indicated that TCE filled PTFE composite exhibited better abrasion resistance. Improvements in the abrasion resistance, however, have not been achieved by short-fiber and particlaute filler reinforcements. From the Taguchi’s experimental findings, optimal combination of control factors were obtained for minimum wear volume and also predictive correlations were proposed. Further, the worn surface morphology of the samples was discussed.

ZrTi2O6 filled PTFE composites for microwave substrate applications

A new kind of ZrTi2O6 filled polytetrafluoroethylene (PTFE) microwave composite substrates was fabricated through the hot-pressing process. The microwave dielectric properties of ZrTi2O6/PTFE composites were measured using stripline resonator method. The relative dielectric constant (er) and loss tangent (tanδ) of the composites increase with an increase of the volume fraction of ZrTi2O6 ceramic (0–46 vol%). The experimental dielectric constants of the composites match well with theoretically predicted values by Lichtenecker mixing rule. As the volume fraction of ZrTi2O6 ceramic increases, the thermal expansion coefficient and the temperature coefficient of dielectric constant decrease. The ZrTi2O6 filled PTFE composite exhibits a dielectric constant of 7.42 with a loss tangent of 0.0022 (10 GHz) at an optimum filler loading of 46 vol%.

Effect of Connectivity on Microwave Dielectric Properties of Low Loss Ceramics Filled PTFE Composites

Effects of connectivity patterns on the dielectric properties of polytetrafluoroethylene (PTFE) composites filled with low-loss Zn-based ceramics (ZnWO4, ZnMoO4) were investigated at microwave frequencies. The dielectric constant (K), dielectric loss (tan δ) and temperature coefficient of resonant frequency (TCF) of the 0–3 connectivity composites were dependent on the type and amount of ceramics. For the composites with 0.2 volume fraction (Vf) of ZnMoO4, the K and tan δ increased with number of connectivity and internal strain, respectively. Typical results of K = 2.99, tan δ = 3.155×10−3 and TCF = 0 ppm/°C were obtained for the 0–2 connectivity composites with 0.2 Vf of ZnMoO4.

The Addition of a Nano-SiO<sub>2</sub> on the Tribological Properties of PTFE Composite

A kind of novel polytetrafluoroethylene (PTFE)-based composite filled with nano SiO2 are developed for sliding tribological applications. The specimens are fabricated with the compression moulding technique. And the mechanical and tribological properties of the composites are investigated. It is demonstrated that these properties are influenced by the content of fillers. The wear resistances of all the developed PTFE composites are much higher than that of pure PTFE with very low coefficients of friction. Among the developed composites, the mixture of PTFE + 30% nano SiO2 exhibits the best combination of properties. The improved tribological performance of nano-SiO2 filled PTFE composites can be attributed to the improved structural integrity of the composites.

Frictional behavior investigation on three types of PTFE composites under oil‐free sliding conditions

PurposeThe purpose of this paper is to investigate the frictional behavior of polytetrafluoroethylene (PTFE) composites under oil‐free sliding conditions.Design/methodology/approachThe friction force and power consumption of pressure packing seals, which were, respectively, made of common filled PTFE, 30 wt% CF (carbon fiber) + PTFE and C/C (carbon/carbon) + PTFE, are studied in a reciprocating oil‐free compressor arrangement. Their coefficient of friction is tested on a block‐on‐ring type tribometer.FindingsThe results indicate that influence of mean sliding velocity on filled PTFE composites is apparently more predominant than the others. The friction force curvilinear path of 30 wt% CF+PTFE is hardly influenced by changing crankshaft turn angle. For C/C+PTFE, the effect of mean piston velocity on friction force is not evident. The results also indicate that the friction coefficient of C/C+PTFE is lower than that of 30 wt% CF+PTFE if their applied normal force exceeds 9.8 N. Furthermore, their variation curve of friction force is little different and the power consumption of C/C+PTFE is slightly higher than that of 30 wt% CF+PTFE.Research limitations/implicationsNeither the effect of real contact area on friction coefficient measured in a tribometer nor the influence of the temperature on friction force and power tested in a compressor is not taken into consideration here.Practical implicationsOwing to its good mechanical performances and frictional behaviors, C/C+PTFE is an optimum and promising material under conditions with sealing pressure up to 10 MPa and sliding velocity exceeding 4.0 m/s.Originality/valueA novel material called C/C+PTFE is considered to make packing rings for oil‐free reciprocating compressors and its friction behaviour is tested on a refitted compressor.

Comparison of alumina and magnesia filled PTFE composites for microwave substrate applications

Flexible microwave substrates have been fabricated using micron size powders of α-Al2O3 and MgO filled in polytetrafluoroethylene (PTFE) matrix through SMECH process, comprising of sigma mixing (SM), extrusion (E), calendering (C) followed by hot pressing (H). Prior to fabrication of the composites, silane coating on the fillers was done to preclude moisture absorption. Filler loading in the PTFE matrix was varied in steps (10–70wt.%) and their effects on the microwave dielectric properties (ε′r and tanδ) at X-band (8.2–12.4GHz) were evaluated using waveguide cavity perturbation technique. Optimum filler loading for both alumina and magnesia filled composites were found out by systematically varying the filler concentration. SEM microgrpahs revealed uniform distribution of filler in the matrix without any delamintaion of stacked calendered tapes. A comparative study of the magnesia filled samples with and without silane coating is also carried out to ascertain the effects of brucite phase formed during silane coating process on the dielectric and moisture absorption properties of composite substrates.

Effects of fibrous fillers on friction and wear properties of polytetrafluoroethylene composites under dry or wet conditions

The friction and wear behavior and mechanism as well as the mechanical properties of polytetrafluoroethylene (PTFE) composites filled with potassium titanate whiskers (PTW) and short carbon fibers (CF) under dry, wet and alkaline conditions were investigated. Experiments indicated that owing to appropriate cooling and boundary lubricating effects, the filled PTFE composites showed much lower frictional coefficient and better wear resistance under alkaline than dry and wet sliding conditions. The wear resistance of carbon-fiber-filled PTFE was much better than that of potassium titanate-whisker-filled PTFE composites in water. Results also showed that the transfer film on counterpart rings was significantly hindered by water and alkali. Hydrophilic-filler-reinforced PTFE composites yield higher wear rate when sliding under water.

Tribological properties of PTFE composites filled with surface-treated carbon fiber

Carbon fibers (CF) were surface treated with concentrated HNO3, silane coupling agent, rare earth solution and rare earth sol, respectively. The friction and wear behavior of polytetrafluoroethylene (PTFE) filled with differently surface treated CF were studied. The worn surfaces of CF/PTFE composites were then examined with scanning electron microscope (SEM). It is found that the wear volume loss of the rare earth sol treated CF filled PTFE composites reaches the lowest value when the modifier concentration is 10 wt%. It is only about 65% of the wear volume loss of the PTFE filled with untreated CF. Among all the treatments to CF, rare earth sol treatment is the most effective and the lowest friction and wear volume loss of CF/PTFE composite is exhibited.