Mechanism of size effects of a filler on the wear behavior of ultrahigh molecular weight polyethylene

Although the size effects of a filler are closely related to the complex multi-level structures of their polymer composites; unfortunately, such relationships remain poorly understood. In this study, we investigated the effects of various sizes (40-600 nm) of silicon carbide (SiC) fillers on the wear behavior of ultrahigh molecular weight polyethylene (UHMWPE) in the presence of the silane coupling agent KH-560. All of these SiC fillers improved the wear resistance of UHMWPE significantly, with a medium size (150 nm) being optimal. To examine the reasons for this behavior, we analyzed the multi-level structures of the samples in terms of their matrix structures (crystalline; amorphous; interphase), matrix-filler interactions (physical adsorption; chemical crosslinking; hybrid network) and the external effects of SiC fillers (bearing loads; transferring frictional heat). The high rigidity and thermal conductivity of SiC fillers and, more importantly, the intrinsic characteristics of the matrix structures (larger crystal grains; higher interphase; stronger amorphous entangled networks) were the key parameters affecting the enhancement in the wear-resistance of the UHMWPE. Herein, we also provide interpretations of the corresponding physical effects. Our results should improve our understanding of the structure-property relationships and, thus, should guide the formula design of UHMWPE composites.     

The tribological properties of SiC whisker-reinforced polyetheretherketone

SiC whisker-reinforced polyetheretherketone (PEEK) composites with different filler proportions were made into block specimens by compression molding. The friction and wear properties of the composites were investigated on a block-on-ring machine by running a plain carbon steel (AISI 1045 steel) ring against the composite block under ambient conditions. The morphologies of the wear traces and wear debris were observed by scanning electron microscopy (SEM). It was found that SiC whisker-reinforced PEEK exhibited considerably lower friction coefficient compared with pure PEEK, while SiC whisker as a filler at a content of 1.25 to 2.5 wt % was very effective in reducing the wear rate of PEEK. Especially, the lowest wear rate was obtained with the composite containing 1.25 wt % SiC whisker. The SEM pictures of the wear traces indicated that PEEK composites undertook abrasive wear that was enhanced with increasing SiC whisker content, while for the frictional couple of carbon steel ring/composite block (reinforced with 1.25 wt % filler), a thin, uniform, and tenacious transfer film was formed on the ring surface. It was also supposed that the differences in the content of SiC whisker as filler could cause the differences in the wear mechanisms of SiC whisker-reinforced PEEK composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2341–2347, 1998     

Effects of a coupling agent on the mechanical and thermal properties of ultrahigh molecular weight polyethylene/nano silicon carbide composites

Ultra‐high‐molecular‐weight polyethylene (UHMWPE)/nano silicon carbide (nano‐SiC) composites were prepared by compression molding. The effects of a coupling agent and the content of the filler on the filler dispersion and the mechanical and thermal properties of the composites were investigated. The results show that the mechanical properties of the composites first increased and then decreased with increasing SiC content. The macromolecular coupling agent exhibited a much better reinforcing effect than the small‐molecule coupling agent. The tensile strength of the composites with 3‐aminopropyltriethoxysilane (KH550), γ‐methacryloxypropyltrimethoxysilane (KH570), and silicone powders reached its maximum value when the silicon carbide (SiC) content was 3%. We found that a web of the UHMWPE/SiC/coupling agent was formed and played a significant role in improving the heat resistance of the composites. In addition, appropriate amounts of SiC could increase the crystallinity of UHMWPE via a process of heterogeneous nucleation. The comprehensive performance of the KH550/silicone/SiC/UHMWPE composites was the best. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication of Polyimide-Modified UHMWPE Composites and Enhancement Effect on Tribological Properties

Polyimide-modified ultrahigh molecular weight polyethylene (UHMWPE) composites were fabricated by hot-press molding process. Mesoscopic morphologies of polyimide/UHMWPE blending systems show high compatibility between the phases of polyimide and UHMWPE when the weight ratio of polyimide is no more than 50?wt%. Investigation of the tribological properties with a reciprocating ball-on-flat contact tribometer shows that the polyimide filler has important effects on the friction and wear behavior of UHMWPE composites. Compared to pure UHMWPE, the composite with 50?wt% polyimide improved tribological properties best and exhibited 43.1% reduction in friction coefficient and 66.7% reduction in wear volume loss.     

Mechanical properties study of micro‐ and nano‐hydroxyapatite reinforced ultrahigh molecular weight polyethylene composites

This is a comparative study between ultrahigh molecular weight polyethylene (UHMWPE) reinforced with micro‐ and nano‐hydroxyapatite (HA) under different filler content. The micro‐ and nano‐HA/UHMWPE composites were prepared by hot‐pressing method, and then compression strength, ball indentation hardness, creep resistance, friction, and wear properties were investigated. To explore mechanisms of these properties, differential scanning calorimetry, infrared spectrum, wettability, and scanning electron microscopy with energy dispersive spectrometry analysis were carried out on the samples. The results demonstrated that UHMWPE reinforced with micro‐ and nano‐HA would improve the ball indentation hardness, compression strength, creep resistance, wettability, and wear behavior. The mechanical properties for both micro‐ and nano‐HA/UHMWPE composites were comparable with pure UHMWPE. The mechanical properties of nano‐HA/UHMWPE composites are better compared with micro‐HA/UHMWPE composites and pure UHMWPE. The optimum filler quantity of micro‐ and nano‐HA/UHMWPE composites is found to be at 15 wt % and 10 wt %, separately. The micro‐ and nano‐HA/UHMWPE composites exhibit a low friction coefficient and good wear resistance at this content. The worn surface of HA/UHMWPE composites shows the wear mechanisms changed from furrow and scratch to surface rupture and delamination when the weight percent of micro‐ and nano‐HA exceed 15 wt % and 10 wt %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42869.     

Thermal properties,rheology and sintering of ultra high molecular weight polyethylene and its composites with polyethylene terephthalate

The addition of polyethylene terephthalate (PET) fibers in ultra high molecular weight polyethylene (UHMWPE) may be a promising approach to achieve improved wear properties in artificial joints. Since UHMWPE/PET composites are processed by compression molding, which involves compaction and sintering of polymeric powders, this article investigates their rheology, thermal properties, and sintering behavior to aid in the identification and selection of optimum processing conditions. Isothermal crystallization kinetics studies have revealed that crystallization of UHMWPE proceeds via heterogeneous nucleation and is governed by two‐dimensional growth. The crystallization rates of the composites were lower than those of the neat material, whereas their ultimate crystallinities were higher. The UHMWPE/PET composites had higher viscosity and elasticity than the neat resin. In the presence of PET fibers the onset of sintering took place at higher temperatures but proceeded at substantially higher rates as compared with pure UHMWPE. A marked discrepancy between the Eshelby‐Frenkel model and experimental sintering data suggests that viscous flow is not the prevailing mechanism for coalescence but rather that enhanced surface area, attributed to the highly developed internal morphology of UHMWPE particles, is the controlling factor. POLYM. ENG. SCI., 45:678–686, 2005. © 2005 Society of Plastics Engineers     

Study on tribological properties of frictional material based aromatic polyamide

The effect of inorganic fillers on the friction and wear behavior of frictional material based poly(m‐phenylene isophthalamide) (PMIA) is investigated. The polymer composites are prepared by compression molding. The friction and wear of PMIA composites are investigated on a block‐on‐ring machine by running the PMIA composite block against plain carbon steel. The morphologies of the worn surface of PMIA composite and the ring counterface are examined by using electron probe microanalysis. It is found that copper compounds including CuCl, CuCl₂, Cu₂O, and CuO filled PMIA exhibit considerably higher friction coefficient than unfilled PMIA, while the wear rate of those composites decrease. Especially, CuCl is the optimal filler in the copper compounds investigated above. The filled PMIA composite containing CuCl, graphite, and short carbon fiber shows the best properties for frictional material. The friction coefficient of CuCl–PMIA composite is higher than that of unfilled PMIA because of the abrasive action of CuCl particle. It is probably the smoother surface of counterpart ring and composite block that resulted in the lower wear rate and friction coefficient of PMIA composite. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2790–2794, 2001     

Processing and characterization of particles reinforced SiOC composites via pyrolysis of polysiloxane with SiC or/and Al fillers

Polysiloxane loaded with SiC as inert filler, and Al as active filler, was pyrolyzed in nitrogen to fabricate SiOC composites, and the processing and properties of the filled SiOC composites were investigated. Adding SiC fillers could reduce the linear shrinkage of filler-free cured polysiloxane in order to obtain monolithic SiC/SiOC composites. The flexural strength of SiC/SiOC composites reached 201.3 MPa at a SiC filler content of 27.6 vol.%. However, SiC/SiOC composites exhibited poor oxidation resistance, thermal shock resistance and high temperature resistance. Al fillers could react with hydrocarbon generated during polysiloxane pyrolysis at 600 °C and N₂ at 800 °C to form Al₄C₃ and AlN, respectively. The volume expansions resulting from these two reactions were in favor of the reduction in linear shrinkage and the improvement in flexural strength of SiC/SiOC composites. The flexural strength of Al-containing SiC/SiOC composites was 1.36 times that of SiC/SiOC composites without Al at an Al filler content of 20 vol.%. The addition of Al fillers remarkably improved the high temperature resistance and oxidation resistance of SiC/SiOC composites, but not thermal shock resistance.     

Elastomer modified phenolic resin-based composites with reduced scale friction: Influence of calcined petroleum coke on tribological and thermo-mechanical behavior

The present investigation deals with the effect of the concentration of calcined petroleum coke (CPC) on the dry sliding wear characteristics of elastomer modified phenolic resin-based friction composites. Other ingredients common in brake formulations like fiber, filler, and solid lubricant were excluded in the present formulations to understand the exclusive effect of the CPC concentration on the frictional, mechanical, and thermal properties of these composites. The composites were fabricated by hot mixing followed by compression molding, and subsequent post-curing. The coefficient of friction (COF) and the specific wear rate of these composites sliding against a cast-iron disc were measured and analyzed. The change in surface topography of these composites before and after sliding operation was investigated by scanning electron microscopy. An effort was made to correlate the surface morphology of these composites before and after sliding with friction and wear behavior. The investigation reveals that CPC inclusion improved the anti-wear behavior as it formed a uniform transfer layer over the rubbing surfaces. In case of optimum CPC loaded (200 phr) composite, the average COF and thermal conductivity values were found to be 0.15 and 0.61 W/m-K, respectively, as compared to 0.12 and 0.25 W/m-K for the base composite (without any CPC).     

原位合成碳化硅-硼化钛复相陶瓷的高温摩擦性能及其磨损机理

以SiC为基体,用TiC和B4C为原料反应生成TiB2,原位合成了SiC-TiB2复相陶瓷.通过测试SiC和SiC-TiB2的高温摩擦系数和比磨损率与温度、外加载荷的关系,研究了SiC-TiB2复相陶瓷的高温摩擦学性能.在空气中,外加载荷为0.2 MPa,摩擦速度为0.3 m/s时,SiC-TiB2复相陶瓷自对偶(SiC-TiB2/SiC-TiB2)高温摩擦呈现较好的高温自润滑性能.温度对SiC-TiB2/SiC-TiB2摩擦系数和比磨损率的影响与载荷有关.载荷为0.4 MPa时,比磨损率最大.用X射线衍射测试了SiC-TiB2/SiC-TiB2磨屑的组成,用扫描电子镜观察了SiC-TiB2/SiC-TiB2磨损断面,发现高温摩擦氧化是TiB2-SiC/SiC-TiB2磨损的主要机理.磨损断面包含摩擦氧化层、过渡层和基体亚表面3层,氧化层和过渡层接触紧密.磨屑具有典型包裹结构,其主要氧化物是无定形氧化硅.平滑的氧化层改进了摩擦表面的塑变性能,缓冲了摩擦应力,减小了高温比磨损率.     

Effect of nano fillers on the properties of polytetrafluoroethylene composites: Experimental and theoretical simulations

Polytetrafluoroethylene (PTFE) has excellent corrosion resistance and a low coefficient of friction; however, its high wear rate and low hardness severely limit its use. In the work, nano particles were used as fillers for PTFE. The composites were prepared by the homogeneous mixing of PTFE and other fillers and sintered at high temperatures. The work aimed to investigate the effect of various nano fillers (nanocarbon powders, graphene, fullerene, nano graphite powders, and nano copper powders) on the mechanical, thermal, and frictional properties of composites. The results of the experiments showed that the addition of graphene could improve the stress and strain values of the composites, and all the nano fillers could improve the thermal conductivity of the PTFE composites. The friction experiments showed that fullerenes could significantly improve the wear resistance of PTFE composites. In the theoretical simulation, the thermal conductivity of PTFE composites was predicted using ANSYS software, with the changes in the temperature and friction force in the friction process. The theoretical simulation results matched with the experimental values, which proved the accuracy of the theoretical simulations.     

Tribological behavior and applications of carbon fiber reinforced ceramic composites as high-performance frictional materials

Due to the favorable tribological, mechanical, chemical, and thermal properties, carbon fiber reinforced ceramic composites, especially carbon fiber reinforced carbon and silicon carbide dual matrix composites (C/C–SiC), has been considered as high-performance frictional materials. In this paper, current applications and recent progress on tribological behavior of C/C–SiC composites are reviewed. The factors affecting the friction and wear properties, including the content of silicon carbide and carbon matrix, carbon fiber preform architecture, as well as the matrix modification by alloy additives and C/C–SiC composites under various test conditions are reviewed. Furthermore, based on the current status of researches, prospect of several technically available solutions for low-cost manufacturing C/C–SiC composites is also proposed.     

Mechanism of filler action in reducing the wear of PTFE polymer by differential scanning calorimetry

Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear‐reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block‐on‐ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea‐frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The role of synthetic and natural fillers on three‐body abrasive wear behaviour of glass fabric–epoxy hybrid composites

Polymer matrix composites are a promising candidate in tribological applications due to possibility of tailoring their properties with special fillers. The comparative performance of Glass–Epoxy (G‐E) composites with influence of synthetic fillers such as graphite (Gr) and silicon carbide (SiC) and biobased natural filler jatropha oil cake (JOC) was experimentally investigated. All the composites were fabricated using vacuum‐assisted resin infusion (VARI) technique. The mechanical properties were studied in accordance with ASTM standards. The three‐body abrasive wear studies were carried out with rubber wheel abrasion tester as per ASTM‐G65 standard. Two different loads namely 22 N and 32 N with different abrading distances viz, 135, 270, 405, and 540 m are test parameters. The results reveal that addition of JOC in G‐E composites has significant influence on wear under varied abrading distance/load. Further, it was found that SiC filled G‐E composites exhibited better wear resistance compared to Gr/JOC filled G‐E composites. The operating wear mechanisms have been studied by using scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of filler type and content and the manufacturing process on the performance of multifunctional carbon/poly-lactide composites

Two nanosized carbonaceous fillers, vapor grown carbon nanofibers and exfoliated graphite nanoplatelets, were used to prepare poly(lactide acid) composites at various concentrations from 0 up to 20 wt.%. The two fillers were also combined in order to explore possible synergistic actions. Two compounding processes, melt mixing and polymer dissolution, and two forming methods, injection and compression molding, were used to manufacture the composites. The flexural properties, impact strength, storage and loss modulus, Vicat softening temperature, and electrical conductivity of neat matrix and composites were determined as a function of the filler type and content, and of the processing method used. The filler dispersion within the polymer matrix, the presence of agglomerates and the existence of voids were studied using field-emission scanning electron microscopy. It is concluded that compounding by polymer dissolution followed by compression molding leads to composites with the lowest percolation threshold and surface conductivity and highest storage modulus whereas extrusion injection molding results in composites with the highest mechanical properties. The results can be used to engineer biodegradable composites with specific properties for targeted applications.     

Mechanical and three‐body abrasive wear behaviour of SiC filled glass‐epoxy composites

Fiber/filler reinforced polymer composites are known to possess high strength and attractive wear resistance in dry sliding conditions. How these composites perform in abrasive wear situations needs a proper understanding. Hence, in this research article the mechanical and three‐body abrasive wear behaviour of E‐glass fabric reinforced epoxy (G‐E) and silicon carbide filled E‐glass fabric reinforced epoxy (SiC‐G‐E) composites are investigated. The mechanical properties were evaluated using Universal testing machine. Three‐body abrasive wear tests are conducted using rubber wheel abrasion tester wherein two different loads and four varying abrading distances are employed. The results showed that the wear volume loss is increased with increase in abrading distance and the specific wear rate decreased with increase in abrading distance/load. However, the presence of SiC particulate fillers in the G‐E composites showed a promising trend. The worn surface features, when examined through scanning electron microscopy, show higher levels of broken glass fiber in G‐E system compared to SiC‐ filled G‐E composites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Experimental and simulated investigation of temperature distribution of UHMWPE laminated composites during hot pressing process

In this article, the influence of molding temperature on the mechanical properties and ballistic impact behavior of the ultrahigh molecular weight polyethylene (UHMWPE) laminated composites has been investigated. The results demonstrate that with the temperature increasing from 80 to 120 °C, the tensile strength decreases while the interlaminar bonding strength increases. The UHMWPE laminated composites manufactured by hot pressing of 75 layers UHMWPE fabrics show excellent ballistic performance when the molding temperature reaches 120 °C, indicating that dominant failure mechanism of the UHMWPE laminated composites are delamination, the fiber tension as well as bulging. Furthermore, a numerical model has been proposed to predict the temperature distribution of the UHMWPE laminated composites for a better understanding of the effect of molding temperature on the ballistic performance. The results show that the simulated results and experimental data are in good agreement. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45874.     

Abrasive wear performance and antibacterial assessment of untreated and treated ZnO‐reinforced polymer composite

In this work, the response of different filler loading of zinc oxide (ZnO) reinforced ultra‐high‐molecular‐weight polyethylene (UHMWPE) on mechanical, abrasive wear, and antibacterial properties were studied. Two variants of untreated ZnO‐reinforced UHMWPE (U‐ZPE) and treated ZnO‐reinforced UHMWPE (T‐ZPE) with aminoproplytriethoxysilane (APTES) were used to compare the improvement of the mechanical, abrasive wear, and antibacterial properties. The abrasive wear and friction behaviors were monitored using a pin‐on‐disc (POD) test rig with different applied loads and sliding speeds against 400‐grit size of silicon carbide (SiC) abrasive paper under dry sliding conditions. The antibacterial assessments of the composites were tested against two common human body bacteria, that is, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Results have shown that T‐ZPE possess higher ultimate tensile strength and elongation at break values as compared to U‐ZPE. Furthermore, the T‐ZPE have higher wear resistance compared to U‐ZPE and pure UHMWPE. The average coefficient of friction (COF) of UHMWPE was not significantly affected by the addition of both untreated and treated ZnO filler. The wear mechanisms were studied under scanning electron microscopy (SEM). Both U‐ZPE and T‐ZPE composites showed active inhibition against E. coli and S. aureus bacteria. POLYM. COMPOS., 34:1020–1032, 2013. © 2013 Society of Plastics Engineers     

The influence of several silicates on the fretting behavior of UHMWPE composites

Five kinds of silicates (attapulgite, kaolin, montnorillonite, synthetic mica, and talc) reinforced ultra-high molecular weight polyethylene (UHMWPE) composites were prepared. The fretting performance of the composites was investigated using an oscillating reciprocating friction and wear tester in a ball-on-plate mode. The thermodynamic property and crystallinity of the composites were evaluated, and the worn morphology was also observed. Result shows that the heat-resistance and the crystallinity of the composites are generally improved. The friction coefficient and mass loss of the composites reduced than those of the neat UHMWPE. Thereinto, the attapulgite/UHMWPE composite shows the best fretting resistance performance. The heat resistance of composites increases due to the reinforcement of silicates. Meantime, the friction load can be distributed by the filler in the matrix. Moreover, the different fretting resistance performance of the composites is due to the different dispersion degree and the interfacial bonding force between the fillers and the UHMWPE matrix.     

Tribological Performance of Bamboo Fabric Reinforced Epoxy Composites

Bamboo fiber is one of the strongest natural fibers with high strength-to-weight and stiffness-to-weight ratios and can be used economically for manufacturing fiber-reinforced composites. In this paper, bamboo fabric-reinforced epoxy composite is manufactured and its tribological properties for load-bearing applications are investigated. Sliding wear tests are conducted using a linear reciprocating tribometer and the effect of dry and lubricated contact conditions, applied load, sliding speed, temperature, and woven fabric direction on the coefficient of friction and wear rate are investigated. A scanning electron microscope is used to define the wear mechanisms at room and elevated temperatures. It is observed that the fabric orientation influences the mechanical and tribological performances of the composite material. Wear rate increases at higher loads and working temperatures; however, the effect of sliding speed is not remarkable, especially under lubricated contact conditions. The results present in this paper can be used for designing bamboo-reinforced epoxy composites for load-bearing applications, under different working conditions.