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Tribological Evaluation of a UHMWPE Hybrid Nanocomposite Coating Reinforced With Nanoclay and Carbon Nanotubes Under Dry Conditions
Abstract
A novel hybrid polymer nanocomposite coating of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with nanoclay (C15A) and carbon nanotubes (CNTs) has been developed to protect metallic mating surfaces in tribological applications. The hybrid nanocomposite coatings were deposited on aluminum substrates using an electrostatic spraying technique. Ball-on-disk wear tests using a 440C stainless steel ball as the counterface were conducted on the coatings under dry conditions to determine the optimum amount of the loadings of the nanofillers and evaluate their tribological performance at different normal loads and linear velocities. Micro-indentation, raman spectroscopy, scanning electron microscopy (SEM), and optical profilometry techniques were used to characterize the coatings in terms of hardness, dispersion of the nanofillers, morphology, and wear mechanisms, respectively. Results showed that the UHMWPE hybrid nanocomposite coating reinforced with 1.5 wt % of C15A nanoclay and 1.5 wt % of CNTs did not fail even until 100,000 cycles at a normal load of 12 N and a linear speed of 0.1 m/s showing a significant improvement in wear resistance as compared to all other coatings evaluated in this study.
... Azam et al. [75] conducted one such study whereby they developed a novel hybrid nanocomposite coating of UHMWPE reinforced with two nanofillers, namely: nanoclay (C15A) and carbon nanotubes (CNTs). They selected nanoclay based upon its excellent mechanical properties and barrier properties. ...
... • Raman spectroscopy: Researchers have also used Raman spectroscopy to ascertain the dispersion of the nanofillers and also to evaluate their interfacial interaction with the UHMWPE matrix. Umar et al. [75,76], used Raman spectroscopy to evaluate the interaction of CNTs with the UHMWPE matrix, based upon the shifting of the peaks corresponding to the G-band to higher wave numbers. The shifting of the G band towards higher frequencies is attributed to the disentanglement of the CNTs in the UHMWPE matrix as a result of polymer penetration into the CNT bundles, resulting in a good load transfer. ...
... Ismaila et al. [69], used Raman spectroscopy to evaluate the dispersion of GNPs within the UHMWPE matrix based upon the presence/absence of the signature peaks related to GNPs in the raman spectra. • Scanning electron microscopy (SEM)/energy dispersive X-Ray analysis (EDX): One of the most common characterization technique used to quantitatively analyze the dispersion of the nanofillers within the UHMWPE matrix is SEM in conjunction with EDX which helps in obtaining the elemental mapping of the nanofillers [63,68,69,75,76]. The combination of these two techniques has also been used to ascertain the failure or the non-failure of the coatings by most of the researchers. ...
In the recent past, polymer coatings have gained the attention of many researchers due to their low cost, their ability to be coated easily on different substrates, low friction and good anti-corrosion properties. Various polymers such as polytetrafluroethylene (PTFE), polyether ether ketone (PEEK), polymethylmethacrylate (PMMA), polyurethane (PU), polyamide (PA), epoxy and ultra-high molecular weight polytheylene (UHMWPE) have been used to develop these coatings to modify the surfaces of different components to protect them from wear and corrosion. However, among all these polymers, UHMWPE stands out as a tribologist’s polymer due to its low friction and high wear resistance. These coatings have found their way into applications ranging from microelectro mechanical systems (MEMS) to demanding tribological applications such as bearings and biomedical applications. Despite its excellent tribological properties, UHMWPE suffers from limitations such as low load bearing capacity and low thermal stability. To overcome these challenges researchers have developed various routes such as developing UHMWPE composite and hybrid composite coatings with several types of nano/micro fillers, developing composite films system and developing dual film systems. The present paper is an effort to summarize these various routes adopted by different researchers to improve the tribological performance of UHMWPE coatings.
... Just like in the case of bulk UHMWPE, it is essential to improve the load bearing capacity of the UHMWPE coating for better performance. One of the strategies used by researchers is to develop UHMWPE nanocomposite and hybrid nanocomposite coatings reinforced with various nanofillers, such as carbon nanotubes (CNTs) [27,28], graphene [29], nanoclay [30], and nanoclay/CNTs [31]. Azam et al. [30] reinforced UHMWPE with different wt % of nanoclay and found that 1.5 wt % nanoclay-reinforced UHMWPE coating did not fail until 100,000 cycles at a normal load of 9 N and a linear speed of 0.1 m/s. ...
... One of the strategies used by researchers is to develop UHMWPE nanocomposite and hybrid nanocomposite coatings reinforced with various nanofillers, such as carbon nanotubes (CNTs) [27,28], graphene [29], nanoclay [30], and nanoclay/CNTs [31]. Azam et al. [30] reinforced UHMWPE with different wt % of nanoclay and found that 1.5 wt % nanoclay-reinforced UHMWPE coating did not fail until 100,000 cycles at a normal load of 9 N and a linear speed of 0.1 m/s. However, the 1.5 wt % nanoclay/UHMWPE coating could not sustain a load of 12 N, whereby it failed immediately. ...
... As can be seen from the flow chart, the procedure is a combination of sonication and magnetic stirring to achieve a good distribution of the alumina particles in UHMWPE matrix. [27,28], graphene [29], nanoclay [30], and nanoclay/CNTs [31]. Azam et al. [30] reinforced UHMWPE with different wt % of nanoclay and found that 1.5 wt % nanoclay-reinforced UHMWPE coating did not fail until 100,000 cycles at a normal load of 9 N and a linear speed of 0.1 m/s. ...
Due to a growing demand for protecting metallic components from wear and tear, polymer coatings are being extensively researched and developed as one of the most effective and efficient solutions to reduce friction and wear in demanding tribological applications. The present study focuses on developing a polymer nanocomposite coating of ultra-high molecular polyethylene (UHMWPE) reinforced with different loadings (0.5, 3, 5, and 10 wt %) of alumina to protect steel surfaces. Wear tests were conducted on the coated samples using a tribometer with a ball-on-disk configuration, sliding against a 440C hardened stainless steel ball as a counterface to evaluate the wear life and the load-bearing capacity of the developed coatings. Micro-indentation, energy dispersive X-ray spectroscopy, scanning electron microscopy, and optical profilometry techniques were used to characterize the coatings in terms of hardness, dispersion of the nanofillers, morphology, and wear mechanisms, respectively. Results showed that the UHMWPE nanocomposite coating reinforced with 3 wt % and 5 wt % of alumina did not fail, even until 250,000 cycles at a normal load of 12 N and a linear speed of 0.1 m/s, showing a significant improvement in wear resistance as compared to the pristine UHMWPE coating.
... Pristine UHMWPE coatings tested under normal loads of 7 and 9 N did not fail after 5000 cycles but failed after~3600 cycles under 12 N normal load [53]. It is worth highlighting that this result is different from those reported by Azam and Samad, where the same UHMWPE coating, coated with the same technique, failed at 5000 cycles under 9 N normal load [54,55]. The processing and grades of UHMWPE can hardly influence tribological performance [56]. ...
... Under water lubrication, the platelet structure of nanoclay formed a torturous path to the diffusion of water molecules, alleviating the softening of the polymer. Instead of a bulk nanocomposite, the same combinations of hybrid nanocomposites were studied in coating form [55]. Since nanocomposite coating has greater hardness, it has 24% higher COF. This secondary hybrid UHMWPE nanocomposite coating exhibited a longer wear life of~100,000 cycles under normal load of 12 N. ...
Polymer nanocomposites with enhanced performances are becoming a trend in the current research field, overcoming the limitations of bulk polymer and meeting the demands of market and society in tribological applications. Polytetrafluoroethylene, poly(ether ether ketone) and ultrahigh molecular weight polyethylene are the most popular polymers in recent research on tribology. Current work comprehensively reviews recent advancements of polymer nanocomposites in tribology. The influence of different types of nanofiller, such as carbon-based nanofiller, silicon-based nanofiller, metal oxide nanofiller and hybrid nanofiller, on the tribological performance of thermoplastic and thermoset nanocomposites is discussed. Since the tribological properties of polymer nanocomposites are not intrinsic but are dependent on sliding conditions, direct comparison between different types of nanofiller or the same nanofiller of different morphologies and structures is not feasible. Friction and wear rate are normalized to indicate relative improvement by different fillers. Emphasis is given to the effect of nanofiller content and surface modification of nanofillers on friction, wear resistance, wear mechanism and transfer film formation of its nanocomposites. Limitations from the previous works are addressed and future research on tribology of polymer nanocomposites is proposed.
... The technical performance of this pad depends on several factors, including but not limited to the tribological, physical, and mechanical properties of selected materials [1 -3]. Moreover, research has proved that a single element cannot fulfill all brake pad requirements since the different function is required in the friction material formation [4]. Similarly, the selection of composite ingredients for pad application depends not only on their function but also on the ingredient cost, processability, availability, and the latest blending techniques, including dimension stability, preforming capability, and mixing [5]. ...
... It was observed that the compressive strength for carbon-based friction materials varies with different formulations. The relationship between the quantity and nature of constituent influences the strength of the composite and hence determines final properties [4]. The varying compressive strength observed in Figure 1 may be attributed to the different concentrations of components in the formulation of each friction material. ...
This research focuses on the mechanical and effect of oil absorption on the tribological properties of carbon-based brake pad material (CBP). Carbon-based materials, including those at a nanosize, are combined for developed brake pad material. The mechanical properties related to wear properties such as compression strength, stiffness, hardness, and absorption properties were determined. The effect of oil absorption on the tribological properties of carbon-based materials was investigated. The obtained properties are compared with that of a ceramic-made brake pad (commercial). The experimental results show that the mechanical and absorption properties of the developed brake pad material varied with the combination and quantity of additives used to develop each brake pad material. CBP material offered higher performance than ceramic-made brake pads. The CBP material showed a higher shear strength of about 110%, 51% enhanced compressive strength, 35% greater modulus, comparative statistical hardness, 98% lesser water intake, and 97% oil absorption rate than ceramic made brake pad. The tribological properties of friction material after soaked in oil proved that absorption properties affect tribological properties of brake pads, which can be attributed to the oil content in the material system. The effect of oil uptakes on wear rate and friction of the commercial brake pad was higher than CBP materials, implying that the loading of carbon-based materials is a viable way to reduce absorption rate, which helps in increasing brake pad performance. The improved properties are suggestive of materials combinations that may be used to develop brake pad materials.
... Ultra-high molecular weight polyethylene (UHMWPE) is one such polymer which shows low friction, higher impact, wear and chemical resistance than its counterparts [4,7,11]. To further improve the mechanical properties of UHMWPE, researchers have reinforced it with different nanofillers independently, such as carbon nanotubes (CNTs) [4,12], nanoclays [13,14], carbon fibers [15,16], ceramic nanoparticles [17,18], graphene [5,19] or in combination to form hybrid nanocomposites [13,20]. Out of these reinforcements, graphene has recently been discovered to offer greater matrix properties enhancement because of its 2D nature, high aspect ratio, high mechanical, thermal and electrical properties [21][22][23]. ...
... Ultra-high molecular weight polyethylene (UHMWPE) is one such polymer which shows low friction, higher impact, wear and chemical resistance than its counterparts [4,7,11]. To further improve the mechanical properties of UHMWPE, researchers have reinforced it with different nanofillers independently, such as carbon nanotubes (CNTs) [4,12], nanoclays [13,14], carbon fibers [15,16], ceramic nanoparticles [17,18], graphene [5,19] or in combination to form hybrid nanocomposites [13,20]. Out of these reinforcements, graphene has recently been discovered to offer greater matrix properties enhancement because of its 2D nature, high aspect ratio, high mechanical, thermal and electrical properties [21][22][23]. ...
Polymer nanocomposite coatings with low friction and high wear resistance are being developed to protect aluminium surfaces against wear and tear during dry and boundary lubrication. In the present study, pure and graphene nanoplatelets (GNPs) reinforced ultra-high molecular weight polyethylene (UHMWPE) nanocomposite coatings are deposited on aluminium thrust bearings. Each bearing makes an ROD contact with a metallic disc counterface to simulate the contact configuration in an actual bearing. A set of tests involving pure and reinforced UHMWPE coatings under dry and liquid contact lubrication is conducted. The wear test results reveal that UHMWPE/1 wt-% GNPs performs better than the reference sample significantly. It reduces the friction and wear of aluminium both in the dry and boundary lubrication conditions at different conditions. The 1 wt-% GNPs reinforcement increases the load-bearing capacity of UHMWPE by 440% in the presence of base oil.
... UHMWPE were seen to be developed in the early 1950s has now gained much popularity due to their superior bio-compatible property [1][2][3][4], self-lubrication, chemically stable [6], and high wear and impact resistance property, which leads of path in biomedical as well as various engineering applications.During the absence of wet lubrication mating parts which are metallic in nature requires some kind of coating to resist wear and friction up to a greater extent and this is done by the researchers by using UHMWPE due to their terrific Tribological characteristics leading to reduced friction and high wear resistance. Researchers adopted a technique wherein nano and hybrid composites were synthesized using UHMWPE with reinforcements in the form of nano fillers like carbon nano tubes [7,8], graphene [9], nano clay [10] and nano clay/CNT [11].Reinforcing UHMWPE with different wt. % of nano clay and conducting Tribological tests upon them showed that the failure of 1.5% reinforcement did not happen until 100000 cycles with a normal load of 9N with a linear speed of 0.1m/s, but at a load of 15N it failed instantly [10]. ...
... Researchers adopted a technique wherein nano and hybrid composites were synthesized using UHMWPE with reinforcements in the form of nano fillers like carbon nano tubes [7,8], graphene [9], nano clay [10] and nano clay/CNT [11].Reinforcing UHMWPE with different wt. % of nano clay and conducting Tribological tests upon them showed that the failure of 1.5% reinforcement did not happen until 100000 cycles with a normal load of 9N with a linear speed of 0.1m/s, but at a load of 15N it failed instantly [10]. To overcome this again UHMWPE with 1.5 wt% nano clay and 1.5wt% CNT were combined to form hybrid composite and observed that the load bearing capacity is increased above 15N [11].Reinforcements are used along with the polymer to produce polyethylene which find their applications in many orthopaedic parts like knee joints and bone joints which leads to the synthesis of ultra-high molecular weight materials which can be used as bio-materials in practice. ...
Results of wear characteristics of Ultra High Molecular Weight Polyethylene (UHMWPE) Polymer Nanocomposites reinforced with micron zinc oxide and Nano zinc oxide are presented. Produced Nano ZnO had flower moprphology (typical flower petal has a length of ∼ 200 nm). Wear rates were acquired using a fabricated wear tester, with applied normal load of 20N, and 40N in rotation and reciprocation modes in dry conditions for 4 hours. In rotation mode neat specific wear rate of UHMWPE being 2.8 x 10⁻⁵ g/Nm for test duration of 2 hours and decreased thereafter to 1.9x10⁻⁵ g/Nm till the end of 4 hours of test duration with applied normal load of 20N. UHMWPE-5% micron ZnO showed highest specific wear rate in both rotation and reciprocation modes. UHMWPE-10% Nano ZnO exhibited intermediate specific wear rate in both rotation and reciprocation modes. UHMWPE-5% NanoZnO possessed lowest wear rate, and smooth worn-out surfaces were observed for UHMWPE-Nano ZnO composites. There has been a 3 fold increase in Ra and Rq values of worn out neat UHMWPE, 1.5 fold increase for micron ZnO composites. However, Ra and Rq values of UHMWPE-10% Nano ZnO composites are decreased. 3D surface images were complementing the test results obtained in this preliminary investigation.
... However, due to their low price, strong tribological qualities, and ease to be coating using simple procedures, polymer-based coatings have been employed as a substitute for lubricating and maintaining metal tribo-pairs. 104 Vlastimil Matějka et al. 105 summarized the influence of SiC particles of 40, 10, and 3 mm on wear behavior on ceramics of potassium titanate. Samples with increasing particle content by the structure of 3.4, 5.6, 9.0, and 14.6 vol.% for each size are fabricated. ...
The use of asbestos in brake pads is being eliminated due to its carcinogenic effect. Due to this, there is a need for better alternative in the brake pad material to replace asbestos fibers. This leads to the development of more natural fibers/filler-based brake pads which are safer to the environment, cheaper, and readily available. Moreover, bio fillers-based brake pads have shown excellent performance compared to asbestos. This paper addresses the different composition of brake pad materials and manufacturing techniques. Common binders like epoxy resin, Phenolic resin-based brake pads were analyzed and its effect on the mechanical, tribological, and thermal performance were critically analyzed. Also, the performance of metal matrix-based brake pad has been analyzed in detail. It has been observed that utilizing natural fibers as a reinforcement provides an excellent braking performance compared to metallic and carbon fiber-based brake pads. This research will open new avenues towards “Net Zero.”
... A novel nanocomposite coating of UHMWPE reinforced with nano clay and C nanotubes was developed to improve tribological properties of UHMWPE. This nanocomposite powder was deposited and fused onto the substrate which increased the melting temperature of the material [131]. ...
The selection of biomaterials as biomedical implants is a significant challenge. Ultra-high molecular weight polyethylene (UHMWPE) and composites of such kind have been extensively used in medical implants, notably in the bearings of the hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the Anterior Cruciate Ligament (ACL) graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and extremely high tensile strength. However, significant problems are observed in UHMWPE based implants, such as wear debris and oxidative degradation. To resolve the issue of wear and to enhance the life of UHMWPE as an implant, in recent years, this field has witnessed numerous innovative methodologies such as biofunctionalization or high temperature melting of UHMWPE to enhance its toughness and strength. The surface functionalization/modification/treatment of UHMWPE is very challenging as it requires optimizing many variables, such as surface tension and wettability, active functional groups on the surface, irradiation, and protein immobilization to successfully improve the mechanical properties of UHMWPE and reduce or eliminate the wear or osteolysis of the UHMWPE implant. Despite these difficulties, several surface roughening, functionalization, and irradiation processing technologies have been developed and applied in the recent past. The basic research and direct industrial applications of such material improvement technology are very significant, as evidenced by the significant number of published papers and patents. However, the available literature on research methodology and techniques related to material property enhancement and protection from wear of UHMWPE is disseminated, and there is a lack of a comprehensive source for the research community to access information on the subject matter. Here we provide an overview of recent developments and core challenges in the surface modification/functionalization/irradiation of UHMWPE and apply these findings to the case study of UHMWPE for ACL repair.
... The averaged Raman spectra of the coated metallic Ti64:W and CoCr:W specimens (pins and disks) as well as the uncoated and coated UHMWPE disks are depicted in Figure 6. While the uncoated metallic specimens were not Raman active, the uncoated UHMWPE disks (Figure 6b, blue) featured characteristic intense peaks at 2848 and 2880 cm −1 as well as weaker peaks at 1065, 1293, 1305, 1435, and 2724 cm −1 [94][95][96][97]. Moreover, the Raman spectra of all DLC-coated specimens showed strong similarities with two pronounced peaks around 1360 and 1560 cm −1 , which are typical positions for the D-and G-bands of amorphous carbon coatings [98]. ...
Diamond-like carbon (DLC) coatings have the potential to reduce implant wear and thus to contribute to avoiding premature failure and increase service life of total knee replacements (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt–chromium–molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While a detailed characterization of the tribological behavior is the subject of part II, part I focusses on the deposition of pure (a‑C:H) and tungsten-doped hydrogen-containing amorphous carbon coatings (a‑C:H:W) and the detailed characterization of their chemical, cytological, mechanical and adhesion behavior. The coatings are fabricated by physical vapor deposition (PVD) and display typical DLC morphology and composition, as verified by focused ion beam scanning electron microscopy and Raman spectroscopy. Their roughness is higher than that of the plain substrates. Initial screening with contact angle and surface tension as well as in vitro testing by indirect and direct application indicate favorable cytocompatibility. The DLC coatings feature excellent mechanical properties with a substantial enhancement of indentation hardness and elastic modulus ratios. The adhesion of the coatings as determined in modified scratch tests can be considered as sufficient for the use in TKAs.
... The consideration of various fillers is required to lead to an interactive impact bringing about an advancement in mechanical and tribological characteristics of the consequential composite. Reasonable improvements on the tribological properties have been observed on such UHMWPE composites with combined reinforcements [11,12]. The several particles that have been employed by scientists for reinforcement upon considering enrichment of the properties of UHMWPE are as follows: carbon fiber [13,14], grapheme/graphene oxide [15,16], carbon nanotube [17][18][19], micro/nano hydroxyapatite (HA) [20,21], nano-Al 2 O 3 [22], nano-SiO 2 [23]. ...
The artificial replacement of hip joints comes into play when an individual is affected by different types of arthritis or sudden trauma. Hip prosthesis involves the usage of UHMWPE as an acetabular element. The articulating surfaces of the joint are governed by different lubrication regimes such as boundary or mixed lubrication in which micro-wear debris is generated in the course of time, eventually leading to osteolysis. Present study attempts to design appropriate composite material for acetabular cups in hip joints using machine learning and evolutionary algorithm. Artificial neural network (ANN) was employed to develop models for UHMWPE composites with multiple nano and micro reinforcements mapping the mechanical and wear resistance of UHMWPE acetabular cup. Published experimental reports of UHMWPE composites with MWCNT, graphene and carbon fiber (CF) were used as a database to develop the ANN models for both mechanical and tribological properties. The models were used as objective optimization functions using genetic algorithm (GA) in single and multi-objective fashions for building composites with enhanced performance. The present materials informatics approach provides some convincing clues for experimental trials.
... Some of these polymers that have been extensively used include polytetrafluoroethylene (PTFE), polyimide (PI) and ultra-high molecular weight polyethylene (UHMWPE) [1][2][3]. Among all the polymers, UHMWPE is one of the best candidates for bearing applications because of its high strength, excellent wear resistance, high corrosion resistance and lower coefficient of friction [4][5][6][7][8]. It has also been extensively used for biomedical applications [9,10]. ...
Taguchi methodology was implemented to optimize and evaluate the effect of process parameters such as the applied pressure and time of holding on the tribological properties of ultra-high molecular weight polyethylene (UHMWPE) nanocomposite reinforced with different loadings of silicon carbide (SiC) nanoparticles. An L9 orthogonal array was used to design experimental matrix in terms of pressure, holding time, and the loading of SiC. UHMWPE/SiC nanocomposites were synthesized via ultrasonication and hot pressing. Pin on disk wear tests were carried out on the composites to evaluate the tribological properties such as specific wear rate and coefficient of friction. Friction and wear response were analyzed using analysis of variance and regression models. The effect of each parameter and optimal process parameters that result in minimum friction and specific wear rate were determined. The confirmation tests carried out verified the validity of the developed experimental design model.
Ultra-High molecular weight polyethylene (UHMW-PE) coatings have been gaining ground in various tribological applications because of their ease of deposition, outstanding wear resistance and low coefficient of friction. To further strengthen these properties, different types of micro/nanofillers such as carbon nanotubes, nanoclay, graphene oxide, alumina either individually (composite) or in combination (hybrid composite) are being added. As a result, these developed composite/hybrid composite coatings present with better mechanical and tribological properties including improved wear resistance and low coefficient of friction. In the current study, vastly found new low-cost fillers, namely, crumb rubber (CR) particles, which constitute majority of polymeric waste, are being explored as a reinforcement. UHMW-PE composite coatings reinforced with different loadings (5, 10 and 15 wt%) of CR were deposited on mild steel coupons using the electrostatic spray coating technique. These coatings’ mechanical and tribological properties were assessed using microhardness testing and ball on disk sliding wear tests, respectively. Results showed that, the composite coating reinforced with 10 wt% CR was able to sustain a considerably high load of 15 N, which was higher than the load bearing capacity of other similar UHMWPE coatings in the literature filled with a variety of fillers (12 N). The improvement in the performance of the coating is attributed to the excellent mechanical properties with a 94% increase in hardness, a 86% increase in the elastic modulus leading to higher H/E and H3/E2 parameters, coupled with the uniform dispersion of CR particles within the UHMWPE matrix.
Plasma treatment is a technique accepted universally for improving the adhesion of coatings to substrates because of its ease of use, environmental friendliness, and its adaptability. Hence, this research aims to further explore this technique and specifically investigate the effect of air–plasma treatment of different substrates (stainless steel, copper, brass, titanium, and aluminum) on the adhesion and tribological properties of an ultra-high molecular weight polyethylene polymer coating deposited on them. Several characterization techniques such as X-ray photoelectron spectroscopy, water contact angle, and roughness measurements are conducted to evaluate the surfaces before and after air–plasma treatment. Results showed that UHMWPE coating deposited on the plasma-treated stainless steel substrates demonstrated the best adhesion and tribological properties. This was attributed to the improved oxidation effect and the carbon cleaning effect of the plasma treatment on the stainless steel substrates as compared to other substrates.
Ultra-high molecular weight polyethylene nanocomposite coatings reinforced with 1 wt.% graphene nanoplatelets were deposited on aluminum substrates. Sliding wear tests with a pin-on-disc configuration were conducted at different temperatures (25 o C, 75 o C, 90 o C, 115 o C, and 125 o C) to evaluate the wear behavior of the coating at elevated temperatures. The ultra-high molecular weight polyethylene/1 wt.% graphene nanoplatelets nanocomposite coating showed an outstanding performance by passing the wear test without failing even until temperatures of 115 o C as compared to the pure ultra-high molecular weight polyethylene coating which failed at a much lower temperature of 75 o C, indicating an improvement in the operating temperature range of ultra-high molecular weight polyethylene by at least 44%.
This book first introduces polymers and polymer composites which are widely used in different industrial and engineering applications where the proper selection of fiber, filler, and polymer can be tailored for particular application. The primary objective of this book is to broaden the knowledge of tribology of polymer composites in a new dimension for Industry 4.0. For instance, the book covers polymer composites used as self-lubricating material used in the automotive industry and other manufacturing equipment to reduce the effect of energy loss due to friction and wear. This book is of interest to researchers and industrial practitioners who work in the field of tribology of polymer composites, manufacturing equipment and production engineering.
Polymer composites are those materials that form a synergistic mechanical advantage when reinforcement fillers are integrated into polymer. This advantage of the multiphase material possesses excellent wear and friction properties, hence found to be amenable with aerospace, automobile, and biomedical applications. The current article emphasizes the Tribological properties of various polymer composites concisely. However, alongside the Tribological advantage, there is a compromise in mechanical properties due to exposure of polymer composites to hazardous environments resulting in degradation and plasticization. With the advent of new manufacturing and processing techniques, by retaining the mechanical properties, the Tribological properties can be enhanced. In the current article, detailed attention to the microscopic and macroscopic Tribological aspects of polymer composites will be emphasized.
This chapter reviews the recent progress in tribological properties of 3D printed polymer nanocomposites and their applications. The printing of thermoplastic composite infused with different sizes of particles was reviewed. The processing of creating a 3D printed nanoparticle reinforced nanocomposite and their structure-property relations were discussed—valid information on several abrasion apparatus for tribological investigation was also provided. The influence of loading particles on the wear resistance and frictional behaviors of 3D printed nanoparticle reinforced nanocomposites were review. Similarly, the effect of applied load, speed (RPM), and sliding distance on the wear resistance and frictional behaviors of pure thermoplastic, including particle-filled composite, were also evaluated. The tribological properties concerning wear and friction were evaluated. The current application of 3D printed nanoparticle reinforced nanocomposites, and their revolutionary scope was also discussed.
High-performance CNTs reinforced polyether ether ketone (CNTs/PEEK) nanocomposites display an excellent combination of mechanical, thermal and tribological properties. It is a challenge to deposit high-performance CNTs/PEEK nanocomposite coatings via the coating techniques based on solution or melting processes due to low solubility and high melting point of PEEK for tribological applications. In this work, the CNTs/PEEK nanocomposite coatings with CNTs contents of 0.1, 0.5, 1.0 and 2.0 wt.% were prepared by flame spraying of mixed PEEK and CNTs powders using mechanical blending (MB) and ultrasound dispersion (UD) methods. The flame sprayed CNTs/PEEK nanocomposite coatings using UD powders preserved good CNTs dispersion, low porosity and surface roughness, adhesive coating-substrate interfaces. The thermal degradation of PEEK ascribed to overheating of in-flight particles and flame-rescanning coatings was limited by good CNTs dispersion in flame spayed CNTs/PEEK nanocomposite coatings with increase of CNT contents. The good dispersion of CNTs aided in initiating crystallization and confined crystalline growth resulting in high crystallinity degree and small crystallite size of PEEK matrix in the flame sprayed CNTs/PEEK nanocomposite coatings. The uniform nanocomposite coatings with well-dispersed CNTs and few PEEK degradation in optimum content of 1.0 wt.% preserved enhanced microhardness and superiorly tribological properties. The well-dispersed CNTs bonding with PEEK matrix enhanced the mechanical strength to restrict the generation of fatigue cracks from defects of voids, which promoted self-lubrication and wear-resistance of flame sprayed CNTs/PEEK nanocomposite coatings.
Ultra-high molecular weight polyethylene (UHMWPE) composite coatings reinforced with different concentrations (1, 3, 6, and 9 wt%) of submicron tungsten carbide (WC) particles were synthesized using electrostatic sprayed method, characterized and evaluated for corrosion resistance in 1 m HCl electrolytic solution. Results showed that the mechanical properties and adhesion strength of the coatings improved with the increasing WC content to an optimum loading of 6 wt%. These properties slightly dropped when the WC content was further increased to 9 wt% due to agglomeration of the WC particles. Furthermore, both the potentiodynamic polarization test and electrochemical impedance spectroscopy measurement confirmed the high corrosion protection efficiency of the UHMWPE/WC composite coatings over the pristine UHMWPE coating to a minimum of 80% improvement. The 1 wt% WC reinforced UHMWPE coating exhibited the highest corrosion resistance due to better dispersion of the WC particles in the matrix.
In-situ fabrication of nanocomposites facilitates the dispersion of nanofillers in organic matrixes by decreasing the agglomeration of nanofillers compared to a mechanical mixing method. UHMWPE nanocomposites filled SiO2 nanospheres (SNS) were in-situ fabricated by a sol-gel method in this work. Their sliding coefficient of friction and wear rate were determined by a high-speed ring-block wear test apparatus against 45# steel under dry friction conditions, and the tribological behaviors at elevated temperature were tested by a slurry abrasion wear configuration. The in-situ filled SiO2 nanospheres presented an excellent dispersion on UHMWPE, and the fabricated SNS/UHMWPE nanocomposites were found a remarkable enhancement in stiffness, glass transition temperature and hydrophobicity. Furthermore, the SNS/UHMWPE nanocomposites exhibited markedly improved tribological performances than the matrix UHMWPE and the referenced sample prepared by a mechanical mixing method: the sliding coefficient of friction was reduced by over 50% than that of the pristine UHMWPE against a 45# steel ring under dry friction, and the mass wear rate was ca. 59% of the UHMWPE matrix determined by a water-bath mortar at an elevated temperature.
Although extensive improvement has been done on the brake pad for vehicles, most recent materials used still encounter wear rate, friction, stopping distance and time deficiencies. In this regards, this study developed a polymer-based nanocomposite brake pad. Here, a combination of carbon-based materials, including those at a nanoscale, was used to produce the brake pad. Tribological performance, such as friction coefficient, wear rate and stopping distances of developed brake pad was investigated using an inertial dynamometer. The results revealed that the stopping distance, the coefficient of friction and wear rate varies with the brake pad formation and velocity. The micrographs show changes in the structural formation after the incorporation of carbon-based fillers. It also shows the smooth structure and uniform dispersion of the carbon fibre. The smooth surface of the worn brake pad is an indication of a tougher structure. Hence, it was deduced that the fabricated polymer-based hybrid composite had good tribological property. This improved property is suggestive of materials that may be successfully used for brake pad application.
In the present work, composites were developed with novel combination of particular fillers and fibers for an automotive brake system. The influence of short carbon fiber (SCF) on wear rate, coefficient of friction (CoF), modulus, compressive strength, hardness, and surface morphology of worn surface were examined. This investigation confirmed that 0.1% multiwalled carbon nanotubes (MWCNTs) reduced wear rate, CoF for all combinations of composite with carbon fiber. Results indicate that 0.1% (MWCNTs) and 10% SCF-filled composite had superior properties. This performance may be attributed to the uniform dispersion of fiber and the synergistic effect of SCF and MWCNTs, acting in concert that formed a more stable structure resulting in a high strength, stiffness, tougher, and high-heat absorption. Scanning electron microscopy (SEM) microstructure subsequently performed show change in structural development with a corresponding increase of the incorporation of SCF and MWCNTs, which eventually explained the improved properties of composite.
To tap the full potential of polymers to be used as tribo-materials under water lubrication, it is very important to improve their resistance to water uptake on the one hand and improve their strength and load bearing capacity on the other so that their performance under these conditions is not deteriorated. Hence, a unique approach of fabricating a hybrid polymer nanocomposite reinforced with nanoclay for improving the resistance to water uptake and carbon nanotubes (CNTs) to improve the mechanical/tribological properties is undertaken. Ultrahigh molecular weight polyethylene (UHMWPE) hybrid nanocomposites were fabricated via ball milling followed by hot pressing method. Functionalized multi-wall CNTs and C15A organoclay were used as nanofillers in UHMWPE matrix. Hybrid nanocomposites were developed with CNT loadings of 0.5, 1.5 and 3.0 wt% while keeping C15A organoclay content fixed at an optimized value of 1.5 wt%. Initially, the hybrid nanocomposites were optimized under dry sliding conditions whereby a loading of 1.5 wt% of CNTs and 1.5 wt% C15A organoclay resulted in the maximum reduction in the specific wear rate by about 64% as compared to pristine UHMWPE. Later, tribological performance of the optimized hybrid nanocomposite was compared with pristine UHMWPE and its UHMWPE nanocomposites under water-lubricated conditions sliding against a 440C stainless steel ball for 150,000 cycles. The specific wear rate showed a reduction by ~46% for the 1.5 wt% CNTs hybrid nanocomposites as compared to pristine UHMWPE under water lubrication. The improved resistance to wear was attributed to the uniform dispersion of both the nanofillers, namely CNTs and C15A organoclay which effectively increased the load bearing capacity of UHMWPE. Moreover, the excellent barrier properties of the platelet-like structure of C15A clay which presented a torturous path for the diffusion of the water molecule in UHMWPE reduced the softening of the surface layer leading to better resistance to wear under water lubrication.
Nanocomposites of ultra-high molecular weight polyethylene (UHMWPE) were developed via the ball milling method followed by hot pressing. Three different organically modified clays of 1.5 wt%, Nanomer I.28E, Nanomer I.30E, and Closite C15A, were used as reinforcements in the UHMWPE matrix. Ball on disc wear tests showed that all of the clay composites resulted in an improved wear resistance when compared to that of pristine UHMWPE. Scanning electron microscopy-Energy dispersion spectroscopy, X-ray diffraction, and optical profilometry are used to characterize the nanocomposites and the wear morphology. Among all the types of tested nanoclays, 1.5 wt% of C15A reinforced UHMWPE nanocomposite exhibited the highest wear resistance and the lowest coefficient of friction. Addition of 1.5 wt% C15A to UHMWPE reduced its wear rate by 41% and the coefficient of friction by 38% under dry sliding conditions. These improvements are attributed to the uniform dispersion of the clay platelets in the polymer matrix, preventing large scale material removal and also to the formation of a thin tenacious, continuous transfer film on the counterface. POLYM. COMPOS., 2016.
The current study is aimed to investigate the tribological properties of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with organoclay Cloisite (C15A). Nanocomposites are prepared using a high energy ball milling process followed by hot pressing. Three different loadings of 0.5 wt.%, 1.5 wt.%, and 3 wt.% of C15A, respectively, are used as reinforcement. Results from the ball-on-disk wear tests showed that nanocomposites reinforced with 1.5 wt.% of C15A exhibited best wear resistance and lower coefficient of friction (COF), with C15A reducing the wear rate by 41% and the COF by 38%, when compared to the pristine UHMWPE. These improvements are attributed to the uniform dispersion of the nanosized clay platelets preventing large-scale material removal and formation of a thin tenacious, continuous transfer film on the counterface for C15A organoclay composites. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical profilometry are used to characterize the morphology of the nanocomposites and the wear tracks. SEM images of worn surfaces indicated more abrasive wear for the case of pristine UHMWPE as compared to organoclay composites.
In the present scenario, polymers are extensively used for manufacturing of sliding components (against metals or other materials) such as gears, bearings, cams, rollers in conveyors etc. which undergo wear and tear. Thus the study of wear behaviour of polymers becomes necessary in order to enhance the life of such components. In the present research work, the adhesive wear characteristics of crystalline polymer Polyacetal (Polyoxymethylene-POM) and semi-crystalline polymer such as Nylon 6, Nylon 66 (aliphatic polyamides) were investigated. Polymers considered for this study are potential candidate materials for rollers in hybrid chains in food processing industry, medical equipments etc. Sliding wear tests were carried out under dry conditions using a pin- on-disc (ASTM G99) arrangement. The wear tests were performed against a mild steel disc (HRB 67) at room temperature under various loads (60, 80, 100N) and sliding speeds (1.8, 2.3, 2.8m/s). Cylindrical shaped polymers of 25 mm diameter were used for the wear tests. Among the three polymers, Polyacetal was observed the least wear rate and coefficient of friction irrespective of load and speed because of its crystalline nature. Nylon 6 exhibits higher frictional coefficient at higher sliding velocity. Frictional heating and subsequent local melting of the polymer apparently play a role on the wear of the polymers.
In this paper, polyester coating as the matrix was combined with 5wt% of clay nanoparticle and nanocomposites coating was applied on the surface of plain carbon steel components by electrostatic device. Coating structure and morphology of nanoparticles were investigated by SEM and TEM. The effect of adding nanoparticles and curing type on the corrosion resistance properties of coatings were investigated by Tafel test. The results of Tafel test shows that coating corrosion resistance is increased highly by adding nanoclay. Furthermore coatings cured in oven show higher corrosion resistance than coatings cured in microwave. The results of wear test show that adding nanoparticles markedly increases wear resistance of nanocomposite coating also, the type of curing affects on this properties.
Ultra-high molecular weight polyethylene (UHMWPE) is the most widely used
biopolymer for articulating surfaces, such as an acetabular cup liner interfacing
with a metal/ceramic femoral head. However, the formation of wear
debris leads to the aseptic loosening of implants. Thus, in order to improve the
life span via enhancing the fretting wear resistance, UHMWPE is reinforced
with ZnO/Ag nanoparticles. It is envisaged that the ZnO/Ag addition will also
exhibit antibacterial properties. In the current study, the synergetic effect of
the reinforcement of ZnO/Ag nanoparticles (0–3 wt.% combinations) on the
fretting wear behavior of a UHMWPE matrix is assessed. The phase characterization
of compression- molded UHMWPE-Ag-ZnO biopolymer nanocomposites
has elicited the retention of starting phases. All samples were
processed at >98% density using compression molding. Silver and ZnO reinforcement
showed enhanced hardness 20.4% for U3A and 42.0% for U3Z.
Fretting wear performance was evaluated at varying loads (5–15 N), keeping
in mind the weight at different joints, with constant frequency (5 Hz) as well
as amplitude of oscillation (100 lm). Laser surface profilometry showed
change of wear volume from 8.6 9 105 mm3 for neat polymer to
5.8 9 105 mm3 with 1 wt.% Ag + 1 wt.% ZnO reinforcement (at 15 N load).
Consequently, the mechanics of resistance offered by Ag and ZnO is delineated
in the UHMWPE matrix. Further, S. aureus viability reduction is 28.7% in
cases with 1 wt.% Ag addition, 42.5% with 1 wt.% ZnO addition, but synergistically
increase to 58.6% and 47.1% when each of Ag and ZnO is added
with 1 wt.% and 3 wt.%, respectively (when compared to that of the
UHMWPE control sample). Increased wear resistance and superior bioactivity
and enhanced anti-bacterial properties of 1 wt.% Ag + 1 wt.% ZnO and 3 wt.%
Ag + 3 wt.% ZnO shows the potential use of ZnO-Ag-UHMWPE biopolymer
composites as an articulating surface.
The cold spray deposition of ultra-high molecular weight polyethylene (UHMWPE) powder mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica was attempted on two different substrates namely polypropylene and aluminum. The coatings with UHMWPE mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica were very contrasting in terms of coating thickness. Nano-ceramic particles played an important role as a bridge bond between the UHMWPE particles. Gas temperature and pressure played an important role in the deposition. The differential scanning calorimetry results of the coatings showed that UHMWPE was melt-crystallized after the coating.
Reduced graphene oxide or graphene was dispersed in ultra high molecular weight polyethylene (UHMWPE) using two methods to prepare nanocomposite films. In pre-reduction method, graphite oxide (GO) was exfoliated and dispersed in organic solvents and reduced to graphene before polymer was added, while reduction of graphene oxide was carried out after polymer addition for in situ reduction method. Raman spectroscopic study reveals that the second method results in better exfoliation of graphene but it has more amorphous content as evident from selected area electron diffraction (SAED) pattern, wide angle X-ray and differential scanning calorimetry (DSC). The nanocomposite film produced by pre-reduction method possesses higher crystallinity (almost the same as that of the pure film) as compared to the in situ method. It shows better modulus (increased from 864 to 1236 MPa), better strength (increased from 12.6 to 22.2 MPa), network hardening and creep resistance (creep strain reduced to 9% from 50% when 40% of maximum load was applied for 72 h) than the pure film. These findings show that graphene can be used for reinforcement of UHMWPE to improve its tensile and creep resistance properties.
In this article, a series of graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) composites are successfully fabricated through an optimized toluene-assisted mixing followed by hot-pressing. The mechanical and tribological properties of pure UHMWPE and the GO/UHMWPE composites are investigated using a micro-hardness tester and a high speed reciprocating friction testing machine. Also, the wear surfaces of GO/UHMWPE composites are observed by a scanning electron microscope (SEM), to analyze the tribological behavior of the GO/UHMWPE composites. The results show that, when the content of GO nanosheets is up to 1.0 wt%, both the hardness and wear resistance of the composites are improved significantly, while the friction coefficient increases lightly. After adding GO, the tribological behavior of the GO/UHMWPE composites transforms from fatigue wear to abrasive wear associated with the generation of a transfer layer on the contact surface, which efficiently reduced the wear rate of the GO/UHMWPE composites.
Two types of modified layered aluminosilicates (montmorillonites) with different grain size and gallery spaces were tested as nanofillers in epoxy coating compositions for a steel substrate. Organophilic montmorillonites, in the amount of 2.5 and 5 wt% were introduced to waterborne and to solvent-type epoxy coating materials (based on bisphenol-A epoxy resins and various curing agents). The results of this work indicate that processing properties of coating compositions (leveling and drying time) as well as mechanical properties of coatings (hardness, scratch and abrasion resistance, adhesion to steel) were positively affected by a layered aluminosilicate nanofiller. Enhanced water resistance (lower water absorbance) of coats, especially those formed from waterborne compositions, has been found.
In the past few decades, there has been a growing demand for inert, wear-resistant, cost efficient, environmental friendly and low friction coatings. Polymer coatings are one of the best candidates to fulfill these demands due to their low density, anticorrosion properties, self-lubricity, low cost and ease of processing. However, some limiting factors such as low load bearing capacity restrict their applications. By keeping in view this limitation, polymer based nanocomposite coatings were developed in the present study by reinforcing ultra-high molecular polyethylene (UHMWPE) with different loadings of C15A nanoclay (0.5, 1.5 and 3 wt%) to improve the tribological performance of the polymer coating. A novel electrostatic powder spraying technique was used to deposit the coatings on an aluminum substrate. Tribological performance of pristine and C15A/UHMWPE nanocomposite coatings, with different loadings of C15A, was evaluated by using a ball-on-disk configuration with a counterface of 440C hardened stainless steel ball at room temperature under dry conditions. After the optimization of nanoclay loading, effect of linear sliding speed (such as 0.1, 0.2, and 0.3 m/s) on the tribological performance of the coating was also evaluated. X-ray diffraction, scanning electron microscopy and optical profilometry techniques were used to characterize the morphology and dispersion of nanoclay in the polymer matrix, evaluate the thickness and understand the wear mechanisms, respectively. It is observed from the results that 1.5 wt% C15A/UHMWPE nanocomposite coating did not fail even until ∼100,000 cycles (sliding distance = 1.3 km) at a normal load of 9 N and a linear sliding speed of 0.1 m/s as compared to the pristine UHMWPE coating which failed early under same conditions. The improvement in the performance of 1.5 wt% C15A/UHMWPE nanocomposite coating is attributed to the resulting exfoliated morphology of the clay platelets in the polymer matrix due to its uniform dispersion that provides an efficient bridging effect, holding the polymer chains together and resisting their easy pull-out.
Polyhydroxyalkanoate (PHA) composites containing multi-walled carbon nanotubes (MWCNTs) were prepared using a process of melt-blending three-dimensional (3D) printing filaments. Maleic anhydride (MA)-grafted polyhydroxyalkanoate (PHA-g-MA) and chemically modified MWCNTs (MWCNTs-COOH) were used to improve the compatibility and dispersibility of the MWCNTs within the PHA matrix. Structural, morphological, thermal and mechanical characterisations revealed dramatic enhancements in the thermal and mechanical properties of the PHA-g-MA/MWCNTs-COOH composites compared with PHA, because of the formation of ester carbonyl groups through the reaction between MA groups of PHA-g-MA and the carboxylic acid groups of the MWCNTs-COOH. For example, with an addition of 1.0 wt% of MWCNTs-COOH, the initial decomposition temperature and tensile strength at failure increased by 72 °C and 16.0 MPa, respectively. Moreover, MWCNTs or MWCNTs-COOH enhanced the antibacterial activity and static dissipative properties of the composites. Composites of PHA-g-MA or PHA containing MWCNTs or MWCNTs-COOH had better antibacterial activities and antistatic properties.
Polyetheretherketone (PEEK) polymers are increasingly used in tribological applications. An important aspect of PEEK tribology is the surface temperature reached during sliding. At present, most knowledge of frictional heating in PEEK is based on post-hoc analysis of debris and wear surfaces. In this study, infrared thermography was used to observe the full field temperature map of PEEK against sapphire counterface during ball-on-disc sliding. The measured temperatures matched closely those predicted by flash temperature models. Additionally, friction studies were performed with steel and sapphire counterfaces. It was observed that PEEK debris readily deposited on steel but not on sapphire. The friction studies also indicated a greater adhesive friction response for PEEK against steel compared to PEEK against sapphire. The transfer of PEEK material to the steel surface may elevate the temperature at the sliding interface. Analysis of transfer films on steel suggests that the transferred PEEK was oriented in the direction of sliding. The deposition of debris and formation of oriented films resembled a high temperature drawing process, which was likely to be due to localized frictional heating. The results of this study illustrate the important role transfer films play in determining both the friction and temperature of the PEEK wear interface.
Polyether ether ketone (PEEK), an engineering polymer with many advantages such as lightweight, high thermal stability, high strength coupled with toughness, has often been used as a substitute for metals in applications such as bearings, piston rings, pumps and even biomaterials. However, in pristine form, PEEK exhibits poor wear resistance and higher coefficient of friction (~ 0.25 to 0.3) leading to frictional losses because of which the usage of PEEK is widely restricted in applications where energy efficiency is of utmost importance. Hence, in this study a thin nanocomposite coating of ultra-high molecular weight polyethylene (UHMWPE) reinforced with carbon nanotubes (CNTs) is deposited using a simple dip coating process on the surface of PEEK to reduce its wear and the coefficient of friction. Different loadings of CNTs (0.1 and 0.2 wt%) with different concentrations of UHMWPE (3 and 5 wt%) are used to deposit nanocomposite coatings on PEEK. Ball-on-disc wear tests with an AISI 440 C stainless steel standard ball as a counterface are performed to evaluate the tribological properties under dry conditions. FESEM, 3D-optical profilometry and raman spectroscopy are used to characterize the coatings in terms of thicknesses, wear morphology and dispersion, respectively. The nanocomposite coating is found to be very effective in improving the tribological properties of PEEK with 3 wt% UHMWPE coating reinforced with 0.2 wt% of CNTs showed a very low coefficient of friction of ~0.09 and a wear life of more than 25000 cycles at a normal load of 9 N and a sliding speed of 0.5 m\s.
The cold spray deposition of ultra-high molecular weight polyethylene (UHMWPE) powder mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica was attempted on two different substrates namely polypropylene and aluminum. The coatings with UHMWPE mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica were very contrasting in terms of coating thickness. Nano-ceramic particles played an important role as a bridge bond between the UHMWPE particles. Gas temperature and pressure played an important role in the deposition. The differential scanning calorimetry results of the coatings showed that UHMWPE was melt-crystallized after the coating.
An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05-0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.
A hydroxyapatite (HA) particulate reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposite is fabricated by internal mixer at 180°C and using of paraffin oil as a processing aid to overcome the high viscosity of melted UHMWPE. The reinforcing effects of nano-HA are investigated on nanomechanical properties of HA/UHMWPE nanocomposites by nanoindentation and nanoscratching methods. Results show that the nanocomposite with 50 wt % nano-HA exhibits a Young's modulus and hardness of 362.5% and 200% higher, and a friction coefficient of 38.86% lower than that of pure UHMWPE, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42052.
Multi-walled carbon nanotubes (MWCNTs) were oxidized by two different acid treatments and further functionalized with itaconic acid (IA). The functionalized MWCNTs were used to fabricate Poly(ethylene terephthalate) (PET) composites by melt mixing. The presence of functional groups on the surface of the treated MWCNTs was confirmed by infrared spectroscopy and thermogravimetric analysis. The MWCNTs oxidized with a concentrated mixture of HNO3 and H2SO4 exhibited more oxygen containing functional groups (OH, COOH) but also suffer larger structural degradation than those oxidized by a mild treatment based on diluted HNO3 followed by H2O2. PET composites were fabricated using the oxidized-only and oxidized followed by functionalization with IA MWCNTs. PET composites fabricated with MWCNT oxidized by mild conditions showed improved tensile strength and failure strain, while harsh MWCNT oxidation render them overly brittle.
Ultra-high molecular weight polyethylene (UHMWPE) coatings on steel substrate were reinforced with 0.05, 0.1 and 0.2 wt% of plasma treated single-walled carbon nanotubes (SWCNTs) to improve their mechanical, thermal and tribological properties. Nanoindentation results showed that the addition of SWCNTs up to 0.2 wt% to the UHMWPE film significantly improved the mechanical properties such as hardness (∼66%) and elastic modulus (∼58%). Wear durability of the reinforced coating increased significantly (more than two orders of magnitude) though with a slight increase in the coefficient of friction (from ∼0.08 for pristine UHMWPE film to ∼0.16 for the nanocomposite).
The morphology, crystallization behavior, electrical conductivity, and thermal stability of polypropylene (PP) modified with disentangled multi-walled carbon nanotubes (MWCNTs) is reported. Slightly oxidized MWCNT clusters were disentangled in solution by mild sonication in the presence of exfoliated α-zirconium phosphate nanoplatelets. The disentangled MWCNTs were isolated using acid-induced coagulation to precipitate the nanoplatelets, and were subsequently reacted with octadecylamine. The recovered functionalized MWCNTs (F-MWCNTs) are disentangled and easily dispersed in a commercial PP matrix, and serve as more efficient nucleating agents than the untreated MWCNTs. The PP/F-MWCNT composites exhibit an extremely low percolation-like transition in electrical conductivity, which is attributed to the preservation of a random dispersion of disentangled F-MWCNTs upon cooling from the melt. The thermal stability of PP in air is also substantially enhanced at loadings below the percolation threshold due to the tremendous interfacial area between the polymer chains and the free radical scavenging F-MWCNTs. The present approach provides an efficient and potentially scalable route for commercial production of conductive semi-crystalline thermoplastics. The method may be adapted to uniformly disperse MWCNTs in other polymer matrices by appropriate selection of surface functionality.
Coatings made from neat vinyl ester and nanoclay reinforced vinyl ester composites are applied onto individual glass fibers as well as rovings to evaluate their barrier resistance against alkali and moisture attack. The fibers coated with clay nanocomposites present a significantly less damage caused by the diffusing alkali ions, giving rise to a much higher residual tensile strength after aging than the fibers without coating or those with a neat polymer coating. The static fatigue test performed on individual fibers verifies the advantage of using nanoclay composite to retard the corrosion process under the combined stress and alkaline environment. Similar beneficial effects of incorporating nanoclay on residual strength are identified for impregnated fiber bundles. The above observations confirm the excellent barrier characteristics of intercalated/exfoliated nanoclay in polymer that are applied in composite structures on both the microscopic and macroscopic scales.
This chapter presents a brief account of the current state of the art in the area of the tribology of polymers and their composites. The classical explanation of friction based upon the "two-term model" is presented. Further, important factors affecting friction and wear of polymers from the design and materials selection perspectives are described in some detail. Tribological trends for polymer composites, both traditional and nanocomposites, are presented using data currently available in the literature. Finally, based on our current understanding of this field, we have speculated upon some future trends and directions in the area of polymer tribology. Our assessment is naturally very subjective and selective given the vast potential for research growth in this field.This review is not meant to be exhaustive and hence, readers will naturally need to consult other chapters presented in this book for a much more detailed knowledge of the area of polymer tribology in general and tribology of nanocomposites in particular.
An analysis has been made of the literature on friction and wear of polymer nanocomposites prepared by compounding nanofillers with molten thermoplastics. A process is described for preparing the nanocomposites with various binders, for example, polar and nonpolar thermoplastics, aliphatic, aromatic, and partially aromatic polymers, as well as amorphous and partially crystalline polymers by reactive extrusion. The most important group of triboengineering nanocomposites includes thermoplastics containing the following fillers, carbon nanomaterials, layered clays, metals, and metal-containing compounds. The introduction of nanofillers into thermoplastics influences the kinetics and mechanism of tribochemical transformations in a friction contact with metals or other materials. Nanofillers significantly affect the physicochemical behavior of macromolecules, as well as the macromolecular transformations, at the conditions of frictional interaction. This can be explained by adsorption (chemisorption) of functional groups found on the particle surface, variations in polymer crystallinity and morphology, constrained molecular (segmental) mobility in macrochains, and catalytic (inhibiting) effects of the additives on the course of contact reactions. As a consequence, alterations occur in the formation of transfer layers and wear debris, along with the parameters of friction. Depending on the polymer, the nature and concentration of the fillers, the latter can either improve or impair the performance parameters of friction pairs.
Functionalized multiwalled carbon nanotubes (F-MWCNTs) were individually dispersed in a commercial polypropylene (PP) matrix using our well-established α-zirconium phosphate (ZrP) nanoplatelet-assisted dispersion approach. The F-MWCNTs remained uniformly dispersed in PP after melt mixing and injection-molding and were found to remarkably enhance modulus and strength at only 0.1 wt % loading. The individual F-MWCNTs were mostly oriented and extended in the flow direction and were shown to be integrated within the crystalline structure of the matrix. The change in mechanical properties is attributed to both the modification in crystal structure due to MWCNT-induced nucleation and the direct reinforcement of crystalline lamellae and amorphous regions by the MWCNTs. We propose that the compatibilized F-MWCNTs exhibit sufficient interfacial interaction with the PP matrix to anchor lamellae stacks and resist interlamellar slip. The F-MWCNTs also reinforce amorphous domains between crystallites and behave as “super”-tie chains, thereby achieving improvement in tensile properties at low MWCNT loading. This approach for nanocomposite preparation is scalable and easily adapted for other thermoplastics by proper MWCNT surface functionalization.
First- and second-order Raman scattering from graphite has been studied. The second-order spectra of single crystals and of highly oriented pyrolytic graphite are continuous and exhibit several well-defined bands which can be attributed to features in the density of vibrational states as determined from current lattice-dynamics models. The density of states deduced from the lattice-dynamics model of Nicklow, Wakabayashi, and Smith provides the best replication of the second-order Raman spectrum, but is nevertheless somewhat deficient in this regard, and in need of improvement. The dependence of the first- and second-order graphite Raman spectra on crystallite size has also been studied for a series of samples with typical dimensions Lc and La as small as 30 Å. With decreasing crystal size the features in the second-order spectrum broaden noticeably and additional broad features appear in both the first- and second-order spectra. The additional first- and second-order features are also attributed to structure in the vibrational density of states and arise from the wave-vector selection-rule relaxation that results from finite-crystal-size effects. Evidence is presented to demonstrate that the above described spectral features are intrinsic and not associated with impurity excitations.
The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
The original work of Strobl and Hagedorn suggesting the presence of a third intermediate phase in semicrystalline polyethylene was revisited. The current study, involving the collection of Raman spectroscopic data on a set of 16 polyethylene samples recorded on two different types of instruments in two different laboratories and employing two different methods of curve fitting to both sets of experimental data, has revealed that the claims in the original paper cannot be asserted. The most important reason leading to this conclusion is a problem incorrectly describing the complicated overlapping spectral structure in the 1000-1200 and 1400-1500 cm(-1) spectral ranges. It is noted that the contribution of the melt in the 1000-1150 cm(-1) range cannot be described by a single line centered around 1080 cm(-1). The present results indicate that the quantification of a third, intermediate, phase in polyethylene is not possible when based on standard Raman spectra.
A series of polymer–clay nanocomposite (PCN) materials that consisted of poly(styrene-co-acrylonitrile) (PSAN) and layered montmorillonite (MMT) clay were successfully prepared by effectively dispersing the inorganic nanolayers of MMT clay into the organic PSAN matrix by a conventional in situ thermal polymerization. First of all, organic styrene and AN monomers at a specific feeding ratio were simultaneously intercalated into the interlayer regions of organophilic clay hosts and followed by a typical free-radical polymerization with benzyl peroxide as initiator. The as-synthesized PCN materials were subsequently characterized by FTIR spectroscopy, wide-angle powder X-ray diffraction, and transmission electron microscopy. The as-prepared PCN materials, in the form of coatings, incorporated with low clay loading (e.g., 1 wt %) on cold-rolled steel, were found to be much superior in corrosion protection over those of bulk PSAN based on a series of standard electrochemical measurements of corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. Molecular weights of PSAN extracted from PCN materials and bulk PSAN were determined by gel permeation chromatography with THF as eluant. Effects of the material composition on the molecular barrier and thermal stability of PSAN along with PCN materials, in the form of both membrane and fine powder, were also studied by molecular permeability analysis, differential scanning calorimetry, and thermogravimetric analysis, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2269–2277, 2004
The Raman spectrum of ultrahigh-molecular-weight polyethylene (UHMWPE) has been obtained in the temperature interval 135–208°C, a region where optical anisotropy was observed to exist. On the basis of our spectroscopic evidence, we believe that ordered regions persist in the melt above the calorimetrically determined melting point, and that part of the polyethylene chain is in an enviroment which is similar to that of the orthorhombic crystal. These ordered domains disappear with increasing temperature, but no calorimetric phase transition is associated with this change. We postulate that the very long relaxation times associated with the highly viscous melt keep the polyethylene chains in ordered environments which persist until decreased viscosity at increased temperature allows long-range segmental motion. Our evidence supports the view that the melt anisotropy of UHMWPE arises from oriented slowly melting superheated crystals and not from a smectic liquid-crystalline phase.
Raman spectra of the CC stretching region of strained gel-spun ultradrawn ultrahighmolecular weight polyethylene fibers were recorded. On the low-wavenumber side of both the asymmetric and symmetric band, an additional broad band appeared during straining of the fiber, indicating the presence of CC bonds exhibiting high strain. The fraction of such CC bonds was estimated to be 40%. At 4% strain, the shifts of the CC stretching bands were found to increase linearly with the initial Young's modulus. From Raman spectra, information about strain distribution can be obtained. Considering the observed differences in strain distribution between fibers produced in a different way, it can be understood why one sample can be drawn to a higher extent without rupture of CC bonds. The results were discussed in conjunction with results of X-ray measurements reported by Prasad and Grubb. It is suggested that the fibers can be described by two crystalline fractions mixed on the molecular level and an additional small amount of a third fraction with a low Young's modulus.
In this study, dry sliding wear characteristics of commercially available poly-ether-imide and its composite were investigated using a pin-on-disc ring. Pin materials are poly-ether-imide with wear resistance (WR-PEI) and 20% glass fibre reinforced poly-ether-imide (PEI + 20% GFR). Disc materials are 30% glass fibre reinforced polyamide 46 (PA 46 + 30% GFR), unfilled poly-ether-imide with general purpose (GP-PEI) and steel disc. Wear tests were carried out at relatively high sliding speeds of 0.5, 1.0 and 1.5 m/s and pressures of 0.69, 1.38 and 2.07 MPa and under atmospheric conditions of temperature and humidity. Friction coefficient and specific wear rate values for different combinations of the materials were obtained and compared. For all material combinations, it was observed that, the coefficient of friction decreases linearly with the increase in applied pressure values. Furthermore, their specific wear rate slightly increases with the increase in sliding speed values. The highest specific wear rate is observed in the combination of PEI + 20% GFR pin and PA 46 + 30% GFR disc materials. The specific wear rate for PEI and PEI composites are in the order of 1 × 10−8 to 1 × 10−6 mm3/(N m). Finally it is concluded that the wear mechanisms is a combination of adhesive and abrasive wear.
The effects of air-plasma treatment, film thickness, normal load and sliding speeds on the tribological properties of a thin film of Ultra-High Molecular Weight Polyethylene (UHMWPE) coated onto a tool steel substrate sliding against a Φ4mm silicon nitride ball was investigated. Wear tests are carried out on a ball-on-disk tribometer. Air-plasma treatment has enhanced the adhesion of the polymer film to the steel substrate which led to an increased wear life (>100,000cycles) and low coefficient of friction (~0.14) of the thin film. A film of optimum thickness of 16.3±2μm shows the maximum wear resistance. The effect of varying loads (0.3, 1, 2 and 4N) and speeds (200, 400, 600, 1000 and 2000rpm) on wear life and coefficient of friction were also studied. The dual-film (UHMWPE/PFPE) on the air-plasma pre-treated tool steel surface further increased the wear life (>200,000cycles) at a load of 4N and a rotational speed of 1000rpm.
A thin layer of Ultra High Molecular Weight Polyethylene (UHMWPE) or UHMWPE+PFPE is coated onto cylindrical aluminium (Al)
pin (4.6mm diametre) surface with the aim of providing wear resistant coating on this soft and tribologically poor metal.
The coefficient of friction and wear life of the coated samples are investigated on a pin-on-disk tribometre under different
normal loads (394–622g) and two sliding speeds (0.1 and 0.31m/s) against uncoated Al disk as the counterface. Both coatings
provide coefficient of friction values in the range of 0.02–0.2 as compared to 0.4–1.0 for uncoated Al. There is tremendous
improvement in the wear life of the pin, with UHMWPE+PFPE film giving wear life approximately twice to thrice higher than
that with only UHMWPE film. A thin polymer film is transferred to the disk surface during sliding providing very long-term
wear life (continuous low coefficient of friction) despite visual removal of the film from the pin surface. The present films
will have applications in gears and bearings as solid or boundary lubricants for automotive and aerospace component.
Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm−1 for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10−20 to 10−4 S/cm. The storage modulus (G′) versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical properties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (Tc) and fraction of PE that was crystalline (Fc) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT.
A considerable number of total-joint replacement devices used in orthopaedic medicine involve articulation between a metallic alloy and ultra-high molecular weight polyethylene (UHMWPE). Though this polymer has excellent wear resistance, the wear particulate that is produced leads to the limited lifetime of the devices—osteolytic bone loss. Crosslinking has been shown to reduce the wear rate of UHMWPE, but can cause a reduction in various mechanical properties such as impact toughness. Previous work by the authors has shown that UHMWPE-based composites have wear resistance comparable to the irradiation-crosslinked polymer. However, the selection of the reinforcing material is complicated both by understanding the mechanical behavior of the filler and also by biocompatibility considerations. Zirconium has been shown to have excellent corrosion resistance and biocompatibility, and the authors have used the material as a reinforcing filler in UHMWPE with promising results. Compression-molded UHMWPE composites with up to 20 wt.% of microsized zirconium particles were investigated with regards to wear behavior and impact toughness. These composites showed a significant reduction in wear compared to unfilled polymer while still maintaining impact toughness. These results reinforce the paradigm of using polymer composites for orthopaedic applications and may provide a viable alternative to the property tradeoffs encountered with irradiation crosslinking.
In the present work, multiwalled carbon nanotube (MWNT) reinforced UHMWPE composite films were prepared by electrostatic spraying followed by consolidation. X-ray diffraction and differential scanning calorimetry studies showed a decrease in the crystallinity of UHMWPE due to the nature of the fabrication process as well as addition of MWNT. Tensile test showed an 82% increase in the Young’s modulus, decrease in stress to failure from 14.3 to 12.4 MPa and strain to failure from 3.9% to 1.4% due to 5% addition of MWNT. Raman spectra showed the presence of compressive stresses in the nanotubes. Fracture surface showed presence of pullout like phenomena in the MWNT reinforced film.
Molecular Weight Polyethylene Composite
- Ultra-High
Ultra-High Molecular Weight Polyethylene Composite," Compos. Part A, 76,
pp. 62-72.
Chapter 1—Tribological Applications of Polymers and Their Composites–Past, Present and Future Prospects
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Tribological Behavior of Polymer Nanocomposites Produced by Dispersion of Nanofillers in Molten Thermoplastic
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