Research on high temperature friction properties of PTFE/Fluorosilicone rubber/silicone rubber

Silicone rubber (MVQ) has excellent heat resistance, but poor high temperature friction stability, which limits its application in the field of high temperature sealing. Polytetrafluoroethylene (PTFE) is self-lubricating, but its compatibility with rubber is relatively weak. In order to improve the high-temperature friction property of silicone rubber, fluorosilicone rubber (FVMQ) was used as a compatibilizer, and PTFE was added to MVQ by mechanical blending. The friction and wear properties of PTFE/FVMQ/MVQ composites at different temperatures were studied. The results show that compared with MVQ, the mechanical properties of PTFE/FVMQ/MVQ composites was basically unchanged, the coefficient of friction was hardly affected by temperature, and the amount of wear decreased with increasing temperature. PTFE/FVMQ/MVQ composites showed excellent high-temperature abrasion resistance. The high-temperature wear mode was mainly changed from abrasive wear to adhesive wear. The molten layer formed by high-temperature friction can prevent air from directly contacting the surface rubber, which inhibited rubber surface oxidation reaction process.     

Friction and wear behavior of PI and PTFE composites for ultrasonic motors

High‐performance polymer‐based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS₂). To explore the wear mechanisms, the tribo‐pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS₂/PTFE, the AF/MoS₂/PI has much better tribological performance under high loads and speeds.     

Processing of aromatic thermosetting copolyesters into foams and bulk parts: characterization and mechanical properties

Fully dense sheets of aromatic thermosetting copolyester (ATSP) have been produced by blending ATSP oligomers, curing the blend to produce foam, grinding the cured material to a powder, followed by sintering of the cured powers via hot press. The resulting product possesses an excellent combination of mechanical strength and high‐temperature performance to help improve part functionality, gain long‐term reliability, and cost savings. Dynamic mechanical analysis of this system featured a glass transition higher than most available performance thermosets and thermoplastic polymers or reversible bonding polymer system described in literature. Compression and tensile properties of the foam and fully dense ATSP structures exceed those of most engineering polymers. Copyright © 2016 John Wiley & Sons, Ltd.     

Composites Based on Polytetrafluoroethylene and Detonation Nanodiamonds: Filler–Matrix Chemical Interaction and Its Effect on a Composite’s Properties

Specific properties of PTFE composites filled with ultradisperse detonation diamonds (UDDs) with different surface chemistries are studied. It is found for the first time that filler in the form of UDDs affects not only the rate of PTFE thermal decomposition in vacuum pyrolysis, but also the chemical composition of the products of degradation. The wear resistance of UDD/PTFE composites is shown to depend strongly on the UDD surface chemistry. The presence of UDDs in a PTFE composite is found to result in perfluorocarbon telomeres, released as a readily condensable fraction upon composite pyrolysis. The chemical interaction between PTFE and UDDs, characterized by an increase in the rate of gas evolution and a change in the desorbed gas’s composition, is found to occur at temperature as low as 380°C. It is shown that the intensity of this interaction depends on the concentration of oxygen-containing surface groups, the efficiency of UDDs in terms of the composite’s wear resistance being reduced due to the presence of these groups. Based on the experimental data, a conclusion is reached about the chemical interaction between UDDs and a PTFE matrix, its dependence on the nanodiamond surface chemistry, and its effect on a composite’s tribology.     

Effect of atomic oxygen irradiation on the structural and tribological characteristics of polytetrafluoroethylene and its composites

Based on the ground‐based simulation facility, the effects of atomic oxygen (AO) irradiation on the structural and tribological properties of pure polytetrafluoroethylene (PTFE) and carbon fiber and MoS₂‐filled PTFE composites were studied by scanning electron microscopy, X‐ray photoelectron spectroscopy, and a ball‐on‐disc tribometer. The results shown that AO irradiation had significant effects on the structural and tribological properties of pure PTFE, in which the surface morphologies, mass loss, friction coefficient, and wear rate had been changed greatly after AO irradiation. However, it was noticeable that the addition of carbon fiber and MoS₂ filler to PTFE could improve the AO resist capacity and tribological properties of PTFE composites significantly. Copyright © 2016 John Wiley & Sons, Ltd.     

The oxidation‐treated interface on tribological properties of carbon fibers‐reinforced PTFE composite under oil‐lubricated condition

The effect of air oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil‐lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF–PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air‐oxidated composites. X‐ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen‐containing groups on CF surfaces was largely increased. The increase in the amount of oxygen‐containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix and large scale rubbing‐off of PTFE was prevented, therefore, the tribological properties of the composite were improved. Copyright © 2009 John Wiley & Sons, Ltd.     

Structure–tribological property relationship of nanoparticles and short carbon fibers reinforced PEEK hybrid composites

In a previous work, the roles of low‐loading, that is, 1 vol %, nano‐SiO₂ particles on the tribological behavior of short carbon fibers (SCFs)/polytetrafluoroethylene (PTFE)/graphite filled polyetheretherketone (PEEK) were studied. In the present work, the effects of nanoparticle content, varying from 1 to 4 vol %, on the structure and the tribological performance of the composite was investigated. The polished cross sections of the composites were inspected using a scanning electron microscope (SEM). The incorporated nanoparticles significantly reduce the friction coefficients of the composite. With low pressure‐sliding velocity (pv) factors, nanoparticle agglomerates seem to exert an abrasive effect on SCF, and thereby lead to high wear rates. Under such conditions, an increase in nanoparticle content decreases the wear resistance. With high pv factors, the nanoparticles remarkably improve the wear resistance of the composite and the nanoparticle contents do not play an important role on the wear resistance. The worn surfaces, transfer films and wear debris of the composites were analyzed. The tribological mechanisms were discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 801–811, 2010     

Comparative study of the effects of nano‐sized and micro‐sized CF and PTFE on the thermal and tribological properties of PEEK composites

The tribological characteristics of PEEK composites fretting against GCr 15 steel were investigated by a SRV‐IV oscillating reciprocating ball‐on‐disk tribometer. In order to clarify the effect of type and size of fillers on the properties of PEEK composites, nano‐sized and micro‐sized CF and PTFE fillers were added to the PEEK matrix. The thermal conductivity, hardness, and fretting wear properties of PEEK composites reinforced by CF or PTFE were comparatively studied. The results showed that the type and size of the fillers have an important effect on both the friction coefficient and wear rate, by affecting their thermal conductivity, hardness, as well as the surface areas of their transfer films. In comparison, the effect on improving the tribological properties of micro‐sized CF was superior to that of nano‐sized CF, while the effect of nano‐sized PTFE was superior to that of micro‐sized PTFE. Considering the acceptable friction coefficient and wear rate of the composite under the fretting wear test, it seemed that 4% nCF, 20% mCF, 2% nPTFE and 10% mPTFE were desired additive proportions. And it also can be found that during the fretting wear test, the abrasive and adhesive wear resulted in accumulative debris at the contacting surface. The transfer films made of debris were formed on the counterfaces.     

Combined effect of fibers and PTFE nanoparticles on improving the fretting wear resistance of UHMWPE‐matrix composites

Ultra‐high molecular weight polyethylene composites reinforced with carbon fibers (CF) and polytetrafluoroethylene (PTFE) were prepared. The effects of fillers on the microstructure and fretting wear behavior of composites were investigated. The results of X‐ray diffraction and scanning electron microscopy measurements indicated that the microstructure of composites were greatly changed, and the distinct interface between fillers and matrix had been formed with the incorporation of CF and PTFE. In addition, results also showed that the simultaneously filled with CF and PTFE at a proper weight fraction contributed to dramatically improving the friction reducing and wear resistance of ultra‐high molecular weight polyethylene. It can be found that there exists synergism between fillers. Copyright © 2015 John Wiley & Sons, Ltd.     

稀土对玻璃纤维填充金属-塑料多层复合材料抗冲击磨损性能的影响

研究了稀土元素处理玻璃纤维填充金属－塑料多层复合材料在冲击载荷、干摩擦条件下的摩擦和磨损性能，并利用扫描电子显微镜（SEM）对磨损表面进行了观察和分析，结果表明，用稀土表面改性剂处理玻璃纤维表面，可以提高玻璃纤维与聚四氟乙烯之间的界面结合力，改善复合材料的界面性能，并有利于在偶件表面形成分布均匀、结合强度高的转移膜，使复合材料与偶件表面之间的对摩减轻，大幅度地降低了复合材料的磨损，从而使复合材料具有优良的摩擦性能和抗冲击磨损性能。     

Structure and tribological properties of Cu–PU–PTFE composite coatings prepared by low‐energy electron beam dispersion with glow discharge

Polytetrafluoroethylene (PTFE) composite coatings doped copper acetate and polyurethane (PU) were prepared on rubber substrate by low‐energy electron beam dispersion technique. The effects of dopant and glow discharge treatment on the surface morphology, structure and tribological properties of the coatings were investigated. The results showed that Cu–PTFE composite coatings form uniform surface and dense column structure with spherical aggregations under glow discharge treatment. PU coating shows the large size of protuberance structure but PU–PTFE coating presents spherical structure. Both of the coatings become relative dense and smooth after discharge treatment, and Cu–PU–PTFE composite coatings possess a smoother surface and lower polar component of surface energy. Cu doping weakens the crystallinity and ordering degree of composite coatings, but glow discharge increases the ordering degree and branched structure of C―H groups. Friction experiment indicated that Cu fails to improve the wear resistance of PTFE coatings but glow discharge treatment can do it. Cu–PU–PTFE coatings after discharge treatment have the higher wear resistance and lower coefficient of friction. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of irradiation dose rate on curing characteristics of carbon fiber/polymer composites by low‐energy electron beam

During in situ low‐energy electron beam (E‐Beam) curing for carbon fiber‐reinforced polymer composite, prepregs undergoes 3 sequenced curing processes, namely E‐Beam‐induced curing, postray curing after irradiation, and thermally induced curing. In this study, the irradiation dose rate (IDR) is demonstrated to be influential on the redistribution of the curing portions in the 3 curing stages and directly influences the interlaminar bonding quality of the stepwise cured laminates. Differential scanning calorimetry results showed that higher IDR resulted in higher temperature of irradiated prepregs, and hence, a higher degree of curing was induced by the E‐Beam within a dose range of 0 to 500 kGy as compared to lower IDRs, which decreased the interlaminar physical adhesive quality between layers. Analysis indicates that other than pure physical adhesion between uncured layers, postray curing can further enhance the interlaminar shear strength for cured laminates by introducing cross‐layer chemical bonding in the interlaminar zone.     

Friction and Wear of Semi-Crystalline Polytetrafluoroethylene with Spherulitic Micro-Morphology

Polytetrafluoroethylene (PTFE) is an important engineering material with a low coefficient of friction but a high rate of wear. As a semi‐crystalline polymer, its wear resistance is related to its micro‐morphology. Friction and wear properties of semi‐crystalline non‐spherulitic PTFE have been widely studied, but no investigation is reported about tribological properties of spherulitic PTFE due to difficulties in finding such properties. In this paper, friction and wear properties of PTFE with spherulitic micro‐morphology are studied for the first time. The results show that, first, under the same experimental condition, when two kinds of PTFE are rubbed against the steel disc, the number and size of debris of spherulitic PTFE are much less and smaller than that of debris of PTFE without spherulitic crystals. This means that the wear resistance of spherulitic PTFE is better than that of semi‐crystalline PTFE without spherulitic micro‐morphology. Second, the friction property of spherulitic PTFE is also different from that of PTFE without spherulitic crystals. Finally, the friction and wear mechanisms of spherulitic PTFE and non‐spherulitic PTFE are compared.     

Effect of solid lubricant particles on the tribological properties of PTFE composites lubricated with natural seawater

An orthogonal test was used to design different mixture ratios of molybdenum disulfide(MoS₂), graphite, and SiO₂ particles, which were filled with polytetrafluoroethylene (PTFE) composite. MoS₂-, graphite-, and SiO₂-modified PTFE was obtained by pressing and sintering, and the processing parameters were determined using progressive studies and experiments. The friction and wear properties of different PTFE composites lubricated with natural seawater were analyzed using an MMU-5G wear tester. A laser scanning confocal microscope was employed to examine the morphological characteristics of the worn surface. Moreover, the influence of particle proportions on the tribological property of composites was analyzed. Results show that the addition of SiO₂, MoS₂, and graphite can increase the bearing capacity, improve the wear resistance, reduce the friction coefficient, and increase the self-lubricating ability of the PTFE matrix.     

The Potential of O‐MMT as a Reinforcing Filler for Uncured and Dynamically Cured PVC/XNBR Composites

Organic montmorillonite modified with quaternary ammonium (O‐MMT) was compounded with uncured and dynamically cured poly(vinyl chloride)/carboxylated nitrile butadiene rubber (PVC/XNBR) composites, using a Brabender Plasticorder at 130°C and 50 rpm rotor speed. The reinforcing efficiency of the O‐MMT was investigated in the uncured PVC/XNBR composite and the dynamically cured PVC/XNBR counterpart. Mixing and dynamic curing of the composites were monitored by typical torque‐time curves derived from a Brabender internal mixer. The torque‐time curves revealed that the dynamic curing process was successful and the incorporation of O‐MMT has no adverse effect on the processibility of the composites. It has been found that the introduction of crosslinks within the rubbery phase in the presence of the O‐MMT has further improved the tensile properties. DMA studies revealed that dynamically cured composite with O‐MMT showed higher storage modulus than the composite without O‐MMT. Furthermore, a one‐step tensile modulus vs. temperature curve and a related one peak tensile loss modulus vs. temperature curve were obtained, consequently, both are characteristics of a miscible polymers system. Further evidence on the composite miscibility was purchased by thermal scans from DSC, which showed a single glass transition temperature of PVC/XNBR composites. This claim was further supported by ATR‐IR spectra which revealed that hydrogen bonding is extensively involved in PVC/XNBR composites. This evidence unveiled the exact nature of the specific interactions responsible for miscibility and hence, enhanced mechanical properties. Furthermore, we proved in our studies the reinforcing role played by layered clay due to better dispersion, as well as improved interactions.     

Structural and tribological properties of polytetrafluoroethylene composites in atomic oxygen environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of glass fiber (GF) and MoS₂ filled polytetrafluoroethylene (PTFE) composites were investigated in a ground‐based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 10¹⁵ cm^–2 s^–1. The structural changes were characterized by XPS and attenuated total‐reflection Fourier transform infrared spectroscopy, and the tribological changes were evaluated by friction and wear tests and SEM analysis of the worn surfaces. It was found that AO irradiation induced the degradation of PTFE molecular chains, and the primary erosion mechanism is collisionally induced rather than chemically induced. The addition of MoS₂ filler significantly increased the AO resistance of PTFE composites. Friction and wear tests indicated that GF and MoS₂ improved the tribological properties of materials before and after AO irradiation. Short GF and MoS₂ exhibited a good synergistic effect for improving the AO resistant and tribological properties of PTFE material. Copyright © 2012 John Wiley & Sons, Ltd.     

聚苯硫醚/聚四氟乙烯复合涂层研究进展

聚苯硫醚、聚四氟乙烯均是耐高温、耐腐蚀的树脂,同时聚四氟乙烯有极低表面能,而聚苯硫醚与金属有良好结合力,结合二者的优点,有望制备出集合耐腐蚀、耐高温、超疏水等优异性能为一体的功能涂层,因此以聚苯硫醚、聚四氟乙烯为主要原料的复合涂料自1992年以来便倍受关注。本文从聚苯硫醚、聚四氟乙烯各自的性能出发,综述了聚苯硫醚/聚四氟乙烯复合涂层三种不同制备工艺:分层涂覆、共混涂覆、梯度涂覆;详细说明了涂层的五大优异性能:耐腐蚀性、超疏水性能、阻垢性能、耐高温性以及耐磨性能,最后本文还描述了聚苯硫醚/聚四氟乙烯复合涂层的广阔应用前景。     

Investigation of sub‐micron size cenosphere fillers and filler loading on the mechanical and tribological peculiarity of polyester composites

This paper investigates the effect of sub‐micron size cenosphere filler and filler loading on mechanical and dry sliding wear property of polyester composites. Composites are fabricated by filling with 10 and 20 wt% of 800 and 200‐nm size of cenosphere filler particles. Neat polyester composite is also prepared for comparison analysis. Dry sliding wear test is conducted for these composites over a range of sliding distance with different sliding velocities and applied loads on a pin‐on‐disc wear test machine. Taguchi methodology and analysis of variance (ANOVA) is used to analyze the friction and wear characteristics of the composites. The artificial neural network (ANN) approach is implemented to the friction and wear data for corroboration. In this work, mechanical properties of composites such as hardness, tensile strength, tensile modulus, flexural strength, and compressive strength revealed that mechanical properties and wear resistance of the composites increase with a decrease in the particle size. The measured Young's moduli are comparable to standard theoretical prediction models. The morphology of worn composite specimens has been examined by scanning electron microscopy to understand the dominant wear mechanisms. Finally, optimal factor settings are determined using a genetic algorithm (GA). Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamic viscoelastic properties of unsintered polytetrafluoroethylene

The molecular motion of unsintered polytetrafluoroethylene (PTFE) was studied by dynamic viscoelastic measurements. From results for variously heat treated suspension polymerized (molding powder) PTFE, the following conclusions are drawn. Molding powder, as received, has a high degree of crystallinity according to calorimetric results and lower magnitude of the γ relaxation, but the behavior of the β relaxation suggests that the crystals are disordered more than those of the sintered PTFE. The β relaxation peak for an emulsion polymerized PTFE (fine powder) occurs at a higher temperature and is sharper than that for the molding powder, so that the crystals of the fine powder are better ordered than that for the molding powder. The behavior of the β relaxation for the radiation induced-polymerized PTFE is affected by polymerization conditions, particularly concentration of emulsifier. It is concluded from the results for the unsintered PTFE polymerized by various methods that the nature of crystalline state is decided during the course of simultaneous polymerization and crystallization. Molding powder as received has a relatively high magnitude of relaxation between 30°C to 180°C, but with little temperature dependence in this temperature range. This relaxation is diminished by gamma-ray irradiation. Since the molding powder has a complicated morphology, the relaxation in this temperature range is attributed to inter-particle friction rather than a relaxation associated with motion on the molecular level.     

Probing the tribological behaviors in water of novel poly(phthalazione ether sulfone ketone) and its composites based on the state of aggregation and the microstructure

In this paper, novel poly(phthalazione ether sulfone ketone) (PPESK) and its composites reinforced with carbon fibers (CFs) were prepared, and their tribological behaviors in pure and sea water were comparatively investigated. Affected by the noncoplanar twisted aromatic structure in the molecular skeleton, the aggregation of the macromolecular chain in PPESK was amorphous, resulting in very high water absorption of PPESK matrix. The invading water molecules led to a sharp decrease in the hardness of PPESK surface, resulting in very high wear rate of PPESK in water. Although CF/PPESK composites had higher water absorption than pure PPESK, their wear processes in water were no longer dominated by high water absorption but by the load‐carrying effect of CFs, ascribed to the good CF/PPESK interfacial adhesion. Therefore, CF/PPESK composites exhibited very low wear rates in the order of 10^?7 mm³/Nm in water, which decreased with the CF content increasing until the content of CFs reached 50%. The results revealed that the most critical factor determining the wear behavior of a fiber‐reinforced polymer composite sliding in water is the fiber/matrix interface but not the water absorption of the polymer matrix. Copyright © 2017 John Wiley & Sons, Ltd.