Friction and wear of rare earths modified carbon fibers filled PTFE composite under dry sliding condition

Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The friction and wear properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under dry sliding condition, were investigated on a block-on-ring M-2000 tribometer. Experimental results revealed that RE treatment largely reduced the friction and wear of CF reinforced PTFE (CF/PTFE) composites. The RE treated composite exhibited the lowest friction and wear under dry sliding. Scanning electron microscopy (SEM) investigation of worn surfaces and transfer films of CF/PTFE composites showed that RE treated CF/PTFE composites had the smoothest worn surface under given load and sliding speed, and a continuous and uniform transfer film formed on the counterface. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RE treatment, and more carboxyl groups were introduced onto CF surfaces after RE treatment. The increase in the amount of oxygen-containing groups increased the interfacial adhesion between CF and PTFE matrix, and accordingly increased the tribological properties of the composite.     

The NMR-MOUSE: quality control of elastomers.

New applications of the NMR-MOUSE (mobile universal surface explorer) to non-destructive quality control of elastomers are reported. One example concern the thermal aging of fast clutches which was probed by measurements of 1H transverse relaxation time. Novel methodological developments show that 1H double-quantum filtered NMR signals can be generated in the inhomogeneous fields of the NMR-MOUSE for characterization of residual dipolar couplings. This technique was applied to characterize reference natural rubber samples with different crosslink density and carbon black and silica fillers.     

Investigation of Carbon Black Network in Natural Rubber with Different Bound Rubber Contents

A new method was applied to modify the surface activity of virginal carbon black (VCB). LA‐57, one kind of hindered amine light stabilizer, was adsorbed onto the carbon black surface through a strong shear force induced by the screws of a HAAKE internal mixer. The modified carbon black (MCB) was characterized by FT‐IR and thermogravimetric analysis (TGA). The bound rubber content of the natural rubber (NR) compounded with MCB and VCB varied with the fraction of LA‐57 on the MCB surface. The nonlinear effect at small strains, generally referred as the Payne effect, was investigated in the rubber compounds based on the different bound rubber contents. The NR compound containing the lowest bound rubber content had an obvious Payne effect. Based on the bound rubber content, the types of filler network varied from direct contact mode to the joint rubber shell mechanism.     

Effect of Carbon Fiber Surface Oxidation on Tribological Properties of PTFE Composite under Oil-Lubricated Conditions

Air-oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil-lubricated conditions 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 the carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen-containing groups on CF surfaces were increased greatly. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix, and large scale rubbing-off of PTFE was prevented; therefore, the tribological properties of the composite were improved.     

Influence of composition of carbonyl iron particles on dynamic mechanical properties of magnetorheological elastomers

Magnetorheological elastomers (MRE) are known as smart materials. However, the magnetorheological (MR) effect of MRE is not high enough at present, which limits its engineering applications. Prior studies have shown that magneto-induced shear storage modulus and MR effect were mainly determined by the performance of the ferromagnetic particles. In this paper, MRE samples were prepared by carbonyl iron particles (CIP) of different compositions based on silicon rubber under external magnetic field. Their microstructures were observed using an optical digital microscope and a scanning electron microscope. The dynamic mechanical properties of MRE samples were measured using a modified dynamic mechanical analyzer under varying magnetic field strength and frequency. The results show that the carbon content of CIP have a greater impact on the dynamic mechanical properties of MRE. The magneto-induced shear storage modulus and MR effect can be increased by selecting CIP of low carbon content. In addition, the damping property is also significantly influenced by the carbon content of the CIP. This study is expected to provide guidance for fabrication of high performance MRE.     

Surface activity studies on carbon-silica dual phase fillers using flow microcalorimetry and multiple probe temperature programmed inverse gas chromatography

Carbon–silica hybrid particles (or carbon silica dual phase fillers (CSDPF)) are used as high performance fillers for elastomers and were originally developed to combine the best aspects of carbon black and silica in one package. In this work a range of such fillers with differing silicon content have been analysed, together with a range of carbon black and silica samples, using flow micro-calorimetry (FMC) and multiple probe temperature programmed inverse gas chromatography (MPTPIGC). The probe set for FMC comprised: ethyl acetate, pyridine, tributylamine; and propan1-ol. The linear increase in both heat and level of adsorption (from dry heptane) of all the probes within the CSDPF silicon content range investigated indicated that the interactions in the FMC were with the silica phase of the CSDPFs. FMC data for a variety of silica reference samples clearly indicates that the linear increase in adsorption activity does not continue beyond ca. 15% w/w silicon. MPTPIGC data obtained using a range of saturated and unsaturated linear and cyclic hydrocarbons together with benzene and pinacolone showed no clear relationship to silicon content. In fact the retention characteristics of CSDPF resembled those of carbon black more than silica. Differences in the carbon phase of the CSDFS and carbon blacks could be resolved using MPTPIGC. This study therefore highlights the complimentary nature of FMC and MPTPIGC in surface analytical studies of fillers.     

Reinforcing mechanism of a novel hydrophilic nano-carbon black in natural rubber latex

Novel water-dispersible carbon nanoparticles (PNASS-CBs) were produced by radical polymerization of sodium 4-styrenesulfonate (NASS) on the surface of carbon black (CB) in the solid state. Scanning electron microscopy (SEM) and the Payne effect results showed that the modified CBs were less likely to form particle networks and thus dispersed better in the natural rubber (NR) matrix, with an average size of 90 nm that was much less than that of the aggregated pristine CBs. We propose that the appropriate modification of CBs mitigates filler-filler interaction and enhances the filler-rubber interaction, which can also be proved by the higher bound rubber contents of the NRL/PNASS-CB composites. When a NRL/PNASS-CB composite is subjected to an outside force, e.g. tensile, more physically absorbed rubber chains (bound rubber) slip and self-adjust their absorbed spots on the CBs’ surface (stress redistribution) in order to jointly share the applied stress. This has a positive effect on the resistance to damage of the rubber molecular chains. Therefore, the addition of the hydrophilic CBs in NR latex leads to significant improvements in the mechanical properties of the NRL/PNASS-CB composites.     

The effect of nitrogen and oxygen plasma on the wear properties and adhesion strength of the diamond-like carbon film coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the PTFE substrates were modified with O₂ and N₂ plasma to enhance the adhesion strength of the DLC film to the substrate. The effect of the plasma pre-treatment on the chemical composition and the surface energy of the plasma pre-treated PTFE surface was investigated by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated PTFE.In the N₂ plasma pre-treatment, the XPS result indicated that defluorination and the nitrogen grafting occurred on the plasma pre-treated PTFE surface, and the water contact angle decreased with increasing the plasma pre-treatment time. In the O₂ plasma pre-treatment, no grafting of the oxygen occurred, and the water contact angle slightly increased with the treatment time. In the pull-out test, the adhesion strength of the DLC film to the PTFE substrate was improved with the plasma pre-treatment to the PTFE substrate, and N₂ plasma pre-treatment was more effective than the O₂ plasma pre-treatment. In the ball-on-disc test, the DLC film with the N₂ plasma pre-treatment showed good wear resistance, compared with that with O₂ plasma pre-treatment.     

Surface modification of diamond-like carbon films with perfluorooctyl functionalities and their surface properties

Photolysis of perfluoroazooctane with diamond-like carbon (DLC) films led to the surface modification to introduce perfluorooctyl functional groups, confirmed by means of FT-IR, XPS, Raman and TOF-SIMS measurements. The DLC films modified with fluorine moieties showed reduction of the surface energy evaluated by contact angle to water, as compared with pristine DLC film. The contact angle of chemically modified DLC film is 105°, comparable to that of polytetrafluoroethylene (PTFE). By monitoring with XPS, we found that the results on the value of fluorine/carbon ratio of fluorinated DLC films depending on irradiation time are consistent with those of contact angle. Chemical modification of DLC films with perfluorooctyl functionalities also led to improvement of their frictional properties. The friction coefficient of the modified film is 0.05 under vacuum condition, whereas that of the pristine film shows very high value (>1).     

The friction and wear properties of divinylbenzene-grafted UHMWPE fiber-filled serpentine/PTFE composite

Divinylbenzene-grafted Ultra-high-molecular-weight polyethylene (UHMWPE) fibers were used to reinforce the Polytetrafluoroethylene (PTFE) composite and the friction and wear behaviors of UHMWPE/PTFE composite were studied on the ring-block machine under vacuum condition. The worn surfaces of specimens were investigated using scanning electron microscopy and energy dispersive spectroscopy (EDS). The results showed that the friction coefficient and temperature of UHMWPE/PTFE composites with surface-treated UHMWPE fiber were apparently lower than that with untreated one. In conclusion, the surface treatment favored the improvement of the higher interface strength and so had good effect on improving the tribological properties of the composites. The dominant wear mechanisms were adhesion wear, plastic deformation, brittle facture, and spalling. The EDS analysis of the worn surface indicated the trend of the tribochemical reaction of the Fe related to the transfer of the PTFE.     

Effect of the Rubber Components on the Mechanical Properties and Braking Performance of Organic Friction Materials

Vegetable oil modified phenolic resin (PF) mixed with four kinds of rubber modifiers, i.e., styrene butadiene rubber, styrene butadiene 2-vinyl pyridine rubber, nitrile butadiene rubber, and carboxyl nitrile butadiene rubber (CNBR), were used as matrices for organic friction materials. The mechanical and thermal degradation properties of all of the blends were investigated. Friction and braking tests of the organic friction materials based on the different matrices and reinforced with hybrid fibers were carried out. The results showed that the resin was most compatible with CNBR; the CNBR/PF blend possessed much higher impact and toughness, and the friction material based on this blend as a matrix exhibited better friction and braking performance. It was concluded that CNBR, the rubber with the most reactive groups, resulted in better mechanical properties of the friction material, and hence optimized the friction, wear and braking performances.     

基于X射线衍射法研究改性脱硫灰基生态橡胶的制备过程及机理

脱硫灰作为半干法脱硫技术主要副产品,其利用难度大且成本高,导致大量脱硫灰以直接堆放和填埋的方式处理,不但造成环境污染,而且浪费潜在资源。橡胶作为广泛应用的聚合物材料,在橡胶制备加工过程中需大量使用填料改善其力学性能、加工性能和填充增容。炭黑与白炭黑作为常用的橡胶填料,其不仅生产工艺繁杂,而且对能源和资源消耗量大,导致成本较高。面对上述问题,如何利用脱硫灰开发一种价格低廉的无机橡胶填料,既是固体废弃物高附加值利用又是资源可持续发展的重要途径之一,也是橡胶企业大幅降低填料成本提高经济效益的重要途径之一。由于脱硫灰属于无机材料,橡胶属于有机材料,为了更好的降低脱硫灰界面与橡胶界面(无机界面/有机界面)的不相容性,需要对脱硫灰进行化学改性处理。以该课题组前期取得的研究成果为基础,创新性以改性脱硫灰取代部分炭黑制备改性脱硫灰基生态橡胶。利用XRD对改性脱硫灰基生态橡胶制备过程各阶段的生产物质进行测试,即丁苯橡胶密炼胶制备阶段、改性脱硫灰基生态橡胶密炼胶制备阶段和改性脱硫灰基生态橡胶制备阶段,从微观层面揭示丁苯橡胶密炼胶制备过程、改性脱硫灰基生态橡胶密炼胶制备过程和改性脱硫灰基生态橡胶制备过程,阐明硫化过程中丁苯橡胶密炼胶与改性脱硫灰的结合机理。同时采用SEM对丁苯橡胶密炼胶与改性脱硫灰基生态橡胶密炼胶的微观形貌进行测试,以进一步佐证所获得的相关机理。结果表明:改性脱硫灰加入丁苯橡胶密炼胶后,改性脱硫灰基生态橡胶密炼胶的最大转矩F max大幅下降、最小转矩F L保持稳定、ΔF=F max-F L显著下降,同时焦烧时间t 10与正硫化时间t 90均缩短。硫化诱导期为0~387 s、硫化反应期为387~1586 s和硫化平坦期为1586~1800 s。在硫化诱导期形成非交联网络结构、硫化反应期前期形成基本交联网络结构、硫化反应期后期完善交联网络结构和硫化平坦期保持交联网络结构。以期为高附加值的脱硫灰资源化利用提供一定理论依据和技术支持。     

Effect of Carbon Black Nature on Vulcanization and Mechanical Properties of Rubber

The influence of the basic properties of carbon black, such as structure, panicle size, and surface activity on the vulcanization and mechanical properties of filled natural rubber compounds was investigated in detail. This is important for a better understanding of the rubber performance and the mechanism of reinforcement. In particular, the effect of carbon black surface activity, which was changed by introducing one kind of hindered amine light stabilizer on rubber reinforcement is emphasized.     

聚四氟乙烯材料表面激光改性与刻蚀

利用波长为248 nm的准分子激光束在不同激光能量密度下照射聚四氟乙烯(PTFE)材料的表面,并用扫描电镜(SEM)、X射线光电子能谱(XPS)、拉曼(Raman)光谱等手段对激光处理前后样品的表面形貌、化学成分和结构进行测量和分析,进而对激光与聚四氟乙烯相互作用的机理进行了研究。实验结果表明,激光辐照使聚四氟乙烯表面产生去氟效应,导致表面碳化、分子链的交联以及含氧基团的产生,随着激光能量密度的增加,C=C双键逐渐形成。这些结构的变化可以导致表面硬度和粘结性增强。激光能量密度的大小对照射后样品表面的物理性质和化学结构有着重要的影响,它是聚合物表面激光改性和烧蚀的关键因素。     

Research on the icephobic properties of fluoropolymer-based materials

Fluoropolymer, because of the extremely low surface energy, could be non-stick to water and thus could be a good candidate as anti-icing materials. In this paper, the icephobic properties of a series of fluoropolymer materials including pristine PTFE plates (P-PTFE), sandblasted PTFE plates (SB-PTFE), two PTFE coatings (SNF-1 and SNF-CO1), a fluorinated room-temperature vulcanized silicone rubber coating (F-RTV) and a fluorinated polyurethane coating (F-PU) have been investigated by using SEM, XPS, ice adhesion strength (tensile and shear) tests, and static and dynamic water contact angle analysis. Results show that the fluoropolymer material with a smooth surface can significantly reduce ice adhesion strength but do not show obvious effect in reducing ice accretion at −8 °C. Fluoropolymers with sub-micron surface structures can improve the hydrophobicity at normal temperature. It leads to an efficient reduction in the ice accretion on the surface at −8 °C, due to the superhydrophobicity of the materials. But the hydrophobicity of this surface descends at a low temperature with high humidity. Consequently, once ice layer formed on the surface, the ice adhesion strength enhanced rapidly due to the existence of the sub-micron structures. Ice adhesion strength of fluoropolymers is highly correlated to CA reduction observed when the temperature was changed from 20 °C to −8 °C. This property is associated with the submicron structure on the surface, which allows water condensed in the interspace between the sub-micron protrudes at a low temperature, and leads to a reduced contact angle, as well as a significantly increased ice adhesion strength.     

Investigation of Transfer Behaviors of Embedded Polytetrafluoroethylene in Different Metal Substrates

Transfer behaviors of molded polytetrafluoroethylene (PTFE) blocks embedded in metal substrates were studied using a DFPM reciprocating tribometer under designed conditions. The substrate properties markedly affected the embedded PTFE transfer behaviors. For instance, the surface friction coefficient when embedded in AISI-1045 steel had evident fluctuations even after 1000 cycles although the friction coefficient decreased with the increase of the sliding cycles. On the other hand, the friction coefficient when the PTFE was embedded in 2024Al was remarkably reduced during the first 200 cycles, reaching a low and stable state. The loads played different roles in the transfer process; a higher load was advantageous for the steel-PTFE embedded composites, but it resulted in the opposite result for the Al-PTFE embedded composites. The motion direction of the GCr15 tribometer steel ball had no remarkable effect on the transfer behaviors. The worn surface of the substrates and the steel ball were observed and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results indicate that the efficiency of second transfer film formation on the 2024Al substrate was better than for the AISI-1045 steel. The adhesion properties of Al enhanced the mechanical transfer of PTFE during the friction process.     

聚丁二烯的固体NMR研究

用脉冲谱仪在室温下测量了不同链节结构的聚丁二烯固体核磁共振氢谱,谱图的差异明显可见。报导了由星型支化样品核磁共振谱分解得到的二个洛伦茨峰的化学位移及强度参数的温度依赖关系。通过测量掺入不同性质炭黑的高顺聚丁二烯样品的FID信号与温度的关系,研究了炭黑与橡胶的相互作用,实验结果表明,不能肯定炭黑对橡胶补强作用的"双壳层模型"。很可能这种补强作用是由于炭黑的加入产生的相分散均匀化的结果,     

基于FTIR与XRD的改性脱硫灰取代部分炭黑 制备复合橡胶的补强机理研究

脱硫灰是半干法脱硫的主要副产品,其利用难度大且成本高,导致大量脱硫灰以直接堆放和填埋的方式处理,不但造成环境污染,而且浪费潜在资源。炭黑(8 000 元·t-1)与白炭黑(6 000 元·t-1)是常用的橡胶补强填料,生产工艺繁杂,消耗大量能源和资源,导致成本较高。面对上述问题,如何利用脱硫灰开发一种价格低廉的无机橡胶补强填料,既是固体废弃物高附加值利用的重要途径之一,也是橡胶企业大幅降低填料成本提高经济效益的重要途径之一。由于脱硫灰属于无机材料,橡胶属于有机材料,为了更好的降低脱硫灰界面与橡胶界面(无机界面/有机界面)的不相容性,需要对脱硫灰进行化学改性处理,以提高脱硫灰代替部分炭黑制备橡胶的力学性能。该研究创新性以硅烷偶联剂Si69、硅烷偶联剂KH550与脱硫灰制备改性脱硫灰,然后以改性脱硫灰取代部分炭黑制备复合橡胶。根据国家与行业标准测试复合橡胶的力学性能,如拉伸强度、撕裂强度和硬度。利用扫描电子显微镜(SEM)对复合橡胶的微观形貌进行测试与分析,傅里叶变换红外光谱仪(FTIR)对改性脱硫灰的组成结构进行测试与分析,X射线衍射仪(XRD)对改性脱硫灰的矿物组成进行测试与分析,以揭示硅烷偶联剂Si69与硅烷偶联剂KH550协同对脱硫灰的改性机理,以及改性脱硫灰对复合橡胶的补强机理。结果表明：采用硅烷偶联剂KH550与硅烷偶联剂Si69协同改性脱硫灰,其取代炭黑的增强效果最佳,即复合橡胶的拉伸强度为20.36 MPa、撕裂强度为45.71 kN·m-1和邵尔A硬度为66;硅烷偶联剂KH550与硅烷偶联剂Si69协同改性脱硫灰,不仅保持脱硫灰依然良好的碱性,有利于对复合橡胶起到增强效果;而且可以改善脱硫灰的表面特性与结构,提高改性脱硫灰与丁苯橡胶的无机界面/有机界面相容性。     

Effects of carbon fiber surface treatment on the tribological properties of 2D woven carbon fabric/polyimide composites

Polyacrylonitrile (PAN)-based carbon fabric (CF) was modified with strong HNO₃ oxidation and then introduced into polyimide (PI) composites. The friction and wear properties of the carbon fabric reinforced polyimide composites (CFRP), sliding against GCr15 stainless steel rings, were investigated on an M-2000 model ring-on-block test rig under dry sliding. Experimental results revealed that the carbon fiber surface treatment largely reduced the friction and wear of the CFRP. Compared with the untreated ones, the surface-modified CF can enhance the tribological properties of CFRP efficiently due to the improved adhesion between the CF and the PI matrix. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after surface treatment, which improved the adhesion between the fiber and the PI matrix and improved the friction-reduction and anti-wear properties of the CFRP. An erratum to this article can be found at     

Effect of an electric field on friction of silicone rubber against steel in the motor base oil's environment

The paper presents the experimental results of research on the effect of an external DC electric field on the coefficient of friction of silicone rubber (elastomer) during its rubbing against a steel surface in the „pin–on–disc” experimental set-up. In the tests there were used silicone rubber samples, the pure PAG and PAO synthetic base oils and their blends with an antiwear (ZDDP) additive. The coefficient of friction μ was determined under conditions with and without an external DC electric field. A DC electric field was generated between a silicone rubber sample and a rotating steel disc (a friction pair). A sample holder was electrically isolated from other metal parts of a tribometer and was connected to one of the poles of a DC power supply, while the other pole was connected by means of the carbon brushes to a rotating steel disc. The experimental results show that the external DC electric field established between the rotating steel disc and a silicone rubber sample causes the coefficient of friction to decrease. It was also found that the coefficient of friction μ depends on the steel disc's angular velocity n, the contact pressure p, and the type of base oil and its blends with the additive used.