Polytetrafluoroethylene Composites Research Articles

Highly expanded fine-cell foam of polylactide/polyhydroxyalkanoate/nano-fibrillated polytetrafluoroethylene composites blown with mold-opening injection molding

To manufacture entirely biodegradable polylactic acid (PLA) foam with a high expansion ratio and a fine-cell structure, we attempted to design economically viable material recipe as well as the injection foam molding (FIM) process. It is well-known that PLA foam featuring high expansion and fine cells is challenging to achieve on FIM technique due to its intrinsically low melt strength. To overcome the inferior foaming characteristics of PLA in this study, nano-fibrils of polytetrafluoroethylene (PTFE) were added expecting an increase of molecular chain entanglements. Another bio-based biodegradable polymer, polyhydroxyalkanoate (PHA) was also blended with PLA to improve the impact strength of the final foams. High-pressure FIM process combined with mold-opening technique was performed to make highly expanded PLA foams with varied material recipes. A constant amount (0.6 wt%) of supercritical nitrogen was injected into FIM system and uniformly mixed with various polymer compositions. The gas-laden melt was injected into the mold cavity to create the foamed PLA samples. Finally, we could demonstrate that it is clearly feasible to manufacture entirely biodegradable PLA foams having a high expansion ratio and a desirable cellular structure using an advanced FIM process.

Friction and wear resistance of polytetrafluoroethylene-based composites reinforced with ceramic particles under aqueous environment

Polytetrafluoroethylene (PTFE) exhibits excellent potential under aqueous lubrication due to its low water absorption, low friction, and good corrosion resistance. However, its poor wear resistance limits its application. In this paper, PTFE was reinforced with different kinds of ceramic particles, and the physical properties were tested using various methods. The tribological behavior of PTFE composites sliding against a super duplex stainless steel was investigated under deionized water and seawater lubrication. The worn surface was examined by scanning electron microscopy, energy-dispersive spectroscopy, and 3D topography. All four kinds of ceramic fillers promoted the crystallinity of the PTFE matrix. Particle-reinforced PTFE showed better tribological performance under seawater than under deionized water. The fragility of ceramic particles played an important role in the anti-wear performance of the PTFE composites. Breaking and shedding of Si3N4 or SiO2 particles would generate and aggravate abrasive wear between friction pairs. With the good crush resistance of SiC particles and seawater lubrication effect, the wear rate of the composite decreased by 80% in seawater compared with pure PTFE. The h-BN-filled PTFE showed a good and stable tribological performance under water and seawater because of the low interlaminar shear strength of h-BN.

Cholic acid is a versatile coating-forming dispersant for electrophoretic deposition of diamond, graphene, carbon dots and polytetrafluoroethylene

Sodium cholate (ChANa) is used for the first time as an advanced charged dispersant and coating-forming molecular agent for electrophoretic deposition (EPD) of different advanced materials, such as diamonds, carbon dots, graphene and polytetrafluoroethylene (PTFE). The amphiphilic structure of ChANa facilitates its adsorption on the materials and allows their good dispersion. The coating formation mechanism is based on gel-forming properties as well as pH-dependent solubility and pH-dependent charge of ChANa. A conceptually novel strategy is proposed for the deposition of PTFE films and composites. PTFE films prepared by EPD show strong adhesion to stainless steel substrates. Potentiodynamic and impedance spectroscopy studies indicate that PTFE films provide corrosion protection of steel. The potentiodynamic studies of the coated stainless steel substrates show significant reduction of corrosion current, whereas impedance spectroscopy show increasing impedance. The film thickness is varied in the range of 1–30 μm by variation of deposition time in the range of 0.5–5 min and deposition voltage in the range of 7–50 V. Building on the strong dispersion power and electrochemical properties of ChANa we demonstrate the feasibility of composite film fabrication by a combined electrodeposition method, which involves electropolymerization of polypyrrole and EPD of diamonds. This investigation opens new and unexplored routes in the electrochemical deposition of advanced materials using ChANa as a co-dispersing and coating-forming agent.

Tribological Behavior of PTFE Composites Filled with PEEK and Nano-ZrO2

In order to study the tribological properties of PTFE modified by hard nanoparticles and soft polymer under dry friction conditions, the tribological properties of polytetrafluoroethylene (PTFE) filled with different volume contents of polyether ether ketone (PEEK) and nano-ZrO2 were investigated at a linear speed of 2 m/s, normal load of 200 N, and ambient temperature conditions for 60 min using a block-on-ring wear tester. A multiple-layer feedforward artificial neutral network (ANN) was used to simulate and analyze the friction coefficient and volume wear rate. The results showed that the friction coefficient and volume wear rate of PTFE composites were effectively reduced when nano-ZrO2 and PEEK were filled separately or simultaneously. The best tribological properties were obtained when the composites were filled with 5–8 vol% nano-ZrO2 and 20 vol% PEEK simultaneously; the volume wear rate was only 1.29 × 10−6 mm3/Nm and the friction coefficient was only 0.15. An ANN can accurately simulate and predict the friction coefficient and volume wear rate of composites, and the predicted results were consistent with the experimental results. A groove appeared in the volume wear rate simulation diagram when the volume content of nano-ZrO2 was about 7% with or without PEEK. This phenomenon indicates that the composites in this region had a lower volume wear rate. Therefore, the addition of nano-ZrO2 and PEEK can effectively improve the tribological properties of PTFE. As a simulation analysis method, an ANN can accurately analyze and predict the tribological properties of composites.

Synergistic enhancement of thermal conductivity for low dielectric constant boron nitride–polytetrafluoroethylene composites by adding small content of graphene nanosheets

Abstract Polymer composite with high thermal conductivity (TC) and low dielectric property has great applications in electronic packaging. Herein, we fabricated a series of boron nitride nanosheets–graphene nanosheets–polytetrafluoroethylene (BNNs–GNs–PTFE, BGP) composites, in which the GNs contents of composites were all constant at 1 wt%, via liquid mixing, followed by cold-pressing and sintering. The results demonstrated that the BGP composites possessed good crystallization, excellent thermal stability, high TC and low dielectric property. When BNNs–GNs content was 25 wt%, the BGP composite had a TC of 1.41 W m−1 K−1. The synergetic effect of BNNs and GNs on the enhancement of composite's TC was investigated with a modified effective medium theory (EMT) model. In addition, we found that the dielectric constant and dielectric loss of BGP composites remained at a low level. The study indicated that adding small content of GNs into BNNs–PTFE composite can significantly enhance the composite's TC, while maintaining its low dielectric constant.

Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

This work provides a lab-scale investigation of the ballistics of solid fuel formulations based on hydroxyl-terminated polybutadiene and loaded with Al-based energetic additives. Tested metal-based fillers span from micron- to nano-sized powders and include oxidizer-containing fuel-rich composites. The latter are obtained by chemical and mechanical processes providing reduced diffusion distance between Al and the oxidizing species source. A thorough pre-burning characterization of the additives is performed. The combustion behaviors of the tested formulations are analyzed considering the solid fuel regression rate and the mass burning rate as the main parameters of interest. A non-metallized formulation is taken as baseline for the relative grading of the tested fuels. Instantaneous and time-average regression rate data are determined by an optical time-resolved technique. The ballistic responses of the fuels are analyzed together with high-speed visualizations of the regressing surface. The fuel formulation loaded with 10 wt.% nano-sized aluminum (ALEX-100) shows a mass burning rate enhancement over the baseline of 55% ± 11% for an oxygen mass flux of 325 ± 20 kg/(m2∙s), but this performance increase nearly disappears as combustion proceeds. Captured high-speed images of the regressing surface show the critical issue of aggregation affecting the ALEX-100-loaded formulation and hindering the metal combustion. The oxidizer-containing composite additives promote metal ignition and (partial) burning in the oxidizer-lean region of the reacting boundary layer. Fuels loaded with 10 wt.% fluoropolymer-coated nano-Al show mass burning rate enhancement over the baseline >40% for oxygen mass flux in the range 325 to 155 kg/(m2∙s). The regression rate data of the fuel composition loaded with nano-sized Al-ammonium perchlorate composite show similar results. In these formulations, the oxidizer content in the fuel grain is <2 wt.%, but it plays a key role in performance enhancement thanks to the reduced metal–oxidizer diffusion distance. Formulations loaded with mechanically activated ALEX-100–polytetrafluoroethylene composites show mass burning rate increases up to 140% ± 20% with metal mass fractions of 30%. This performance is achieved with the fluoropolymer mass fraction in the additive of 45%.

Separation of Water-Oil Emulsions Using Composite Membranes with a Cellulose Acetate Surface Layer

Composite polytetrafluoroethylene – cellulose acetate membranes containing 8 to 19% of the latter by weight, depending on the number of composite layers, were obtained by spraying cellulose acetate suspended in acetone on the surface of a polytetrafluoroethylene substrate. It was found that the wettability of the surface layer of the membrane with a drop of distilled water increased as a result of the deposition of cellulose acetate on the surface of the initial membrane. A decrease in the specific flux of membranes from 4613 to 96 dm3 /(m2· hr) depending on the number of layers after the deposition of cellulose acetate was observed. It is shown that membrane modification leads to an increase in retention capacity of oil products from an oil-in-water emulsion from 84.0 to 99.9 %, while the size of the smallest particles separated by the membrane decreases after modification from 450 nm to 207 nm. A decrease in the absolute value of the ζ -potential with a decrease in the concentration of petroleum products in the emulsion was also detected.

Complications and relapses after alloplasty of large and giant hernia of the esophageal aperture of the diaphragm

The review of the literature presents the content analysis of surgical treatment of large and giant hernia of the esophageal aperture of the diaphragm as well as the analyses of complications when using the main methods of hernioplasty. Alloplasty of the esophageal aperture of the diaphragm remains a large and unresolved surgical problem, as evidenced by the analyzed literature sources, mainly reviews and clinical recommendations.Firstly, alloplasty can cause postoperative complications with a frequency of up to 20%, especially when using rigid polypropylene and composite polytetrafluoroethylene mesh implants with circular paraesophageal fixation. Modern biological nets now show high incidence of anatomical relapses, so most specialists continue to use synthetic implants, of which the most promising ones are lightweight, mesh, partially absorbable structures.Secondly, clear indications for alloplasty have not been developed, for example, according to the size of the hernia of the esophageal opening in the diaphragm, which is the main risk factor for relapses.Thirdly, it is still not clear what indicator should be used to estimate the size of hernia of the esophageal aperture of the diaphragm and, therefore, it is not clearly defined which hernias are considered small, which are large and which are giant, despite the fact that the three terms constantly appear in the medical literature.Fourthly, the optimal technique for alloplasty has not been determined with large and especially giant hernias, which would prevent anatomical relapses, and at the same time would not cause postoperative complications.It is necessary to outline the following ways to solve these problems: to develop effective and at the same time safe methods of alloplasty of large and giant hernias; to determine clear indications for alloplasty of the esophageal opening of the diaphragm, depending on the size of hernias; to create an appropriate, applied classification of hernias of the esophageal aperture of the diaphragm.

Role of reinforcement types and silica nanoparticles on tribofilm growth at PTFE-Steel interface

Abstract Tribological behaviors of polytetrafluoroethylene (PTFE) reinforced with carbon fibers (CF), aramid fibers (AF) and hybrid “CF + AF” were comparatively investigated. It is demonstrated that the hybrid composites reinforced with “CF + AF” exhibit greatly enhanced wear resistance, when compared to the composites reinforced only with CF or AF. Adding only 0.3 vol% silica (SiO2) nanoparticles into the hybrid composites further reduces wear rate by up to 47.3%. Mechanochemistry of PTFE molecules and nanostructures of the tribofilms were comprehensively explored. Our work provides direct evidence that SiO2 nanoparticles released from the composites are compacted into the tribofilms, while the reinforcement types exert an important influence on mechanochemistry of PTFE molecules. This work puts forward new strategies for developing highly wear-resistant PTFE composites via regulating tribo-physical and -chemical actions.

Preparation and characterization of silica aerogel/polytetrafluoroethylene composites

In order to improve their thermal insulation performance, silica aerogel reinforced polytetrafluoroethylene (PTFE) composites with 10–30 wt% silica aerogel were prepared and tested. The morphology, density, structure and thermal properties of the composites were characterized through scanning electron microscopy, infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller analysis, thermo-gravimetric analysis (TGA) and thermal conductivity analysis. A theoretical model of the effective thermal conductivity (ETC) was developed based on the three-level homogenisation theory. It was found that the density of the composites decreases linearly with the mass fractions of silica aerogel. The composites showed remarkable smaller pore radius (1–10 nm) when compared to that of the pure silica aerogel (10–35 nm). The FTIR and TG results confirmed that the reaction of silica aerogel and PTFE occurs during the mixture or heating stage. But the reaction did not effect the structure of the composites. Moreover, the ETC of the composites along the silica aerogel contents can be divided into two stages, where the critical content is 18 wt%. The lowest thermal conductivity can reach 0.13 W m−1·K−1. The ETC of the composites predicted by the theoretical model is in good agreement with those experiment results. The volume fractions of the PTFE in the silica aerogel pore are 87% and 73% for the two stages, respectively, and mainly the large pores on the surface of the silica aerogel particles are filled by PTFE.

Tribological performance of graphite-filled polyimide and PTFE composites in oil-lubricated three-body abrasive conditions

Graphite filled polytetrafluoroethylene (PTFE) and polyimide (PI) composites were tested against tool steel under nominal contact pressure of 6.32 MPa and sliding speed of 1.91 m/s in clean ISO 46 lubricant, and also contaminated lubricant with 4200 ppm of silica sand. Pin-on-disk test results show higher friction and wear of the tribopair in the contaminated condition. Micromechanical properties of the bulk polymers were measured using nanoindentation technique, and softening of the material at elevated temperatures was measured. SEM analysis of the contacting surfaces before and after testing showed abrasive wear as the dominant wear mechanism, and microcutting was a less pronounced wear mechanism in the case of PI composite in contaminated test condition. EDS analysis showed that there was no film transfer from polymers to the countersurface, however it indicated higher oxidation on the wear track of the steel disk slid against PI. Particle embedding in the polymer was shown by EDS and is the reason for scratches seen on the steel disk wear tracks. Both polymers are found to be suitable materials from a tribological standpoint for bearing pad applications.

Bioinspired Design of LDH‐Based Mobile Building Materials with Enhanced Mechanical and Ultraviolet‐Shielding Performance

AbstractGlass fiber reinforced polytetrafluoroethylene composites (PTFE/GF composites) with the excellent performance have been given considerable attention due to their increasing applications in large architecture areas such as stadiums, amusement parks, parking lots, etc. However, the brittleness of glass fiber can hinder the performance of PTFE/GF composites. The PTFE/MLDH (modified ZnAl‐layered double hydroxide)/GF composites inspired by layer‐layer structure are prepared via the multi‐layered dipping method, which consists of GF acting as a reinforcement, PTFE acting as matrix, and MLDH acting as the layer‐layer structure. The results of study show that the high strength and surperflexibility of PTFE/MLDH/GF composites are higher than pure PTFE/GF composites. Especially, when the PTFE/MLDH/GF composites contain 1.6 wt% MLDH, the folding endurance reaches up to 39 035 times, the tensile strength reaches up to 163.57 MPa, and strain reaches up to 8.33%. More significantly, the strength and surperflexibility are illustrated by a mechanism model and it is used to further broaden the application of PTFE/GF composites in mobile building materials. Moreover, it is discovered that the PTFE/MLDH/GF composites have unique translucent performance and excellent ultraviolet‐shielding properties in this study, which further broaden its range of applications.

Ultralow Wear PTFE-Based Polymer Composites—The Role of Water and Tribochemistry

The role of water in the tribochemical mechanisms of ultralow wear polytetrafluoroethylene (PTFE) composites was investigated by studying 10 and 20 wt % polyether ether ketone (PEEK)-filled and 5 w...

Friction and wear characterization of graphite/Polytetrafluoroethylene composites against stainless steel: A comparative investigation under different environments

The friction and wear characteristics of Polytetrafluoroethylene composites filled with 15 wt.% and 25 wt.% graphite were investigated against stainless steel under dry sliding and in aqueous environments. A pin on disc tribometer was employed for experimentation at room temperature. The friction performance of 15 wt.% Graphite/Polytetrafluoroethylene proved better than 25 wt.% Graphite/Polytetrafluoroethylene under all conditions, however the wear performance was better for 25 wt. % Graphite/Polytetrafluoroethylene. Moreover, the tribological behaviour of all the composites enhanced in natural sea water environment. An average COF (0.02) and wear rate (1.27 × 10-5mm3/Nm) were attained for 15 wt. % Graphite/Polytetrafluoroethylene in sea water; and an average COF (0.0293) and wear rate (5.2 × 10-6mm3/Nm) were obtained for 25 wt. % Graphite/Polytetrafluoroethylene in sea water. From SEM analysis it was revealed that the better tribological performance of graphite/Polytetrafluoroethylene in sea water is due to the formation of lubricious films on the surfaces in sea water.

Structure and Thermophysical Characteristics of Polytetrafluoroethylene Composites with Few-Layer Graphene Nanoplatelets

The structure, composition, and thermophysical properties of a PTFE composite with few-layer graphene nanoplatelets have been studied by IR spectroscopy, Raman spectroscopy, and differential scanning calorimetry. Small addition of graphite nanoplatelets (2–6 wt %) have been shown to increase the melting point, enthalpy of melting, and degree of crystallinity of PTFE. This effect is attributed to the fact that graphene nanoplatelets serve as centers of additional crystallization of PTFE from the mixture.

Newly developed polytetrafluoroethylene composites based on F8261-modified Li2Mg2.88Ca0.12TiO6 powder

Li2Mg2.88Ca0.12TiO6 (LMCT) was modified by silane coupling agent (C14H19F13O3Si, F8261), and then filled in polytetrafluoroethylene suspension (PTFE) using hot treating approach. The weight fraction of LMCT varied from 30 to 70 wt %. XRD patterns presented the crystal phase of LMCT powders. The analyses of TEM, XPS, and FTIR were performed to characterize the surface states of LMCT fillers. The effects of LMCT filling content on the microstructure and dielectric properties were also investigated. Several theoretical models were discussed and compared with the dielectric constant of LMCT/PTFE substrates with respect to different LMCT content. Furthermore, the temperature and frequency dependence of dielectric constant were also considered on the composites. At last, the LMCT/PTFE composite substrates possessed relatively high dielectric constant (εr = 4.33) and extremely low dielectric loss (tan δ = 0.001) at filler loading of 50 wt % LMCT.

Surface modification of halloysite nanotubes grafted by dodecylamine and their application in reinforcing polytetrafluoroethylene

AbstractThe modification of halloysite nanotubes (HNTs) as fillers is very effective at improving the performance of polymers. A novel modification of HNTs through grafting dodecylamine onto their surfaces was conducted here. Owing to the improvement in dispersibility of HNTs in polytetrafluoroethylene (PTFE), the mechanical properties and wear resistance (in particular) of the dodecylamine-modified HNT-filled PTFE composite were enhanced significantly.

Modification of Si3N4 ceramic powders and fabrication of Si3N4/PTFE composite substrate with high thermal conductivity

Abstract Si3N4 filled polytetrafluoroethylene (PTFE) composites were prepared for microwave composite substrates. The analyses of Si3N4 powder by XPS and FTIR confirmed the successful grafting of Si3N4 powder by F8261. The effects of Si3N4 content on the microstructure, density, moisture absorption, thermal conductivity and microwave dielectric properties (er, tan δ) of Si3N4/PTFE composites were investigated. With an increase of Si3N4 content, the density, dielectric constant and moisture absorption increase. The composite filled with the modified ceramic powders have better dielectric properties, and the powders are more compatible with PTFE. Different models are used to predict the thermal conductivity of the composite substrate. When the content of Si3N4 ceramic filler is 62 vol% (70 wt%), the prepared Si3N4/PTFE composite exhibits excellent low dielectric loss (tan δ = 0.0014), low dielectric constant (er = 4.03), high thermal conductivity (λ = 1.3 W/m·K) and relatively low water absorption (0.032%).

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.

The effect of different layered materials on the tribological properties of PTFE composites

Two-dimensional (2D) lamellar materials have unique molecular structures and mechanical properties, among which molybdenum disulfide (MoS2) and graphitic carbon nitride (g-C3N4) with different interaction forces served as reinforcing phase for polytetrafluoroethylene (PTFE) composites in the present study. Thermal stability, tribological and thermomechanical properties of composites were comprehensively investigated. It was demonstrated that g-C3N4 improved elastic deformation resistance and thermal degradation characteristics. The addition of g-C3N4 significantly enhanced anti-wear performance under different loads and speeds. The results indicated that PTFE composites reinforced by g-C3N4 were provided with better properties because the bonding strength of g-C3N4 derived from hydrogen bonds (H-bonds) was stronger than that of MoS2 with van der Waals force. Consequently, g-C3N4 exhibited better thermomechanical and tribological properties. The result of this work is expected to provide a new kind of functional filler for enhancing the tribological properties of polymer composites.