Wear properties of 3‐aminopropyltriethoxysilane‐functionalized carbon nanotubes reinforced ultra high molecular weight polyethylene nanocomposites

Ultra high molecular weight polyethylene (UHMWPE) is extensively used as a material in various high‐end applications with superior mechanical properties. Carbon nanotubes (CNTs) reinforced UHMWPE (CNT/UHMWPE) nanocomposite is a promising material that can compensate for the weak durability of UHMWPE. In this study, multiwalled carbon nanotubes were oxidized and silanized using acid mixture and 3‐aminopropyltriethoxysilane, respectively, to improve the interfacial strength between CNTs and UHMWPE. The CNT/UHMWPE nanocomposite was fabricated using these oxidized and silanized CNTs. The treatment effect of CNTs on the wear behavior of the CNT/UHMWPE nanocomposites was investigated through wear tests. The oxidization and silanization of CNTs were confirmed by infrared spectroscopy. Scanning electron microscope analysis showed that the silane‐treated CNT/UHMWPE nanocomposites showed better dispersion and interfacial adhesion between UHMWPE and CNTs becaue of the newly formed functional groups on the CNTs. The friction coefficient and wear rate of silanized CNT/UHMWPE nanocomposite were also found to be lower than those of raw UHMWPE and oxidized CNT/UHMWPE nanocomposite. CNTs were functionalized using oxidation and silanization methods to improve the interfacial adhesion between CNTs and UHMWPE. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

UHMWPE/CNTs复合体系及其纤维的研究进展

综述了超高分子量聚乙烯(UHMWPE)、碳纳米管(CNTs)、UHMWPE/CNTs复合体系及其纤维的研究现状,以及CNTs的添加对UHMWPE/CNTs复合体系及其纤维性能的影响;添加CNTs可有效提高UHM-WPE的耐磨性、电学性能、力学性能以及UHMWPE纤维的抗蠕变性能和热稳定性能;指出CNTs对UHM-WPE改性过程中存在的主要问题是CNTs分散性差,CNTs的生产成本高,UHMWPE/CNTs的改性机理有待进一步深入,并进一步拓宽UHMWPE/CNTs复合体系及其纤维的应用领域。     

UHMWPE在人工髋关节中的磨损机制及改性研究

分析了超高分子量聚乙烯(UHMWPE)基人工髋关节假体松动失效的主要因素。介绍了UHMWPE在人工关节中的磨损机制,以及降低UHMWPE磨损最常用的方法,包括辐射交联改性、α-维E抗氧化法、复合增强以及人工关节润滑等。     

Ultradrawing properties of ultrahigh‐molecular weight polyethylene/functionalized carbon nanotube fibers and transmittance properties of their gel solutions

The influences of the dispersion level of carbon nanotubes (CNTs) and functionalized CNTs on the transmittance properties of ultrahigh‐molecular weight polyethylene (UHMWPE) gel solutions and on ultradrawing properties of their as‐prepared fibers are reported. The transmittance properties suggest that the dispersion level of functionalized CNTs in UHMWPE/functionalized CNTs gel solution is significantly better than plain CNTs in UHMWPE/CNTs gel solutions. The orientation factors, achievable draw ratios, tensile strength (σ_f), and modulus (E) values of UHMWPE/CNTs (F_xC_y) and UHMWPE/functionalized CNTs (F_xC_f‐y) as‐prepared fiber specimens reached a maximum value as their CNT and functionalized CNT contents approached optimum contents at 0.00015 and 0.0001 wt%, respectively. The σ_f and E values of both F_xC_0.0012 and F_xC_f‐0.001 series fiber specimens prepared at their optimum CNT and functionalized CNT contents reached another maximum as their UHMWPE approached optimum UHMWPE concentration of 1.7 wt%. Possible reasons accounting for these interesting properties are proposed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

超高相对分子质量聚乙烯/碳纳米管复合纤维的制备

利用冻胶纺丝的方法制备了超高相对分子质量聚乙烯／碳纳米管(UHMWPE／CNTs)复合纤维,以高锰酸钾和硫酸为氧化剂对CNTs进行纯化处理,用DNZ-201钛酸酯对纯化处理后的CNTs进行功能化处理。采用TEM、SEM和FTIR对CNTs的形态、基团变化和CNTs在UHMWPE中的分散情况进行测试。结果表明,该氧化剂对CNTs的纯化有良好的效果,可以除去大部分附在CNTs上的杂质,产生了有利于功能化的有机基团;SEM和TEM测试结果表明,功能化处理后CNTs可以较为均匀地分散在UHMWPE基体中,没有出现明显的CNTs的团聚现象,而且使UHMWPE大分子排列趋于规整。     

A novel technique for the development of acetabular cup by cold isostatic compaction and sintering of UHMWPE powder with optimized processing parameters

Life of a metal on ultra-high molecular weight polyethylene (UHMWPE) total hip replacement is often limited to 10–15 years, due to wear loss and aseptic loosening. Due to its high melt flow index, UHMWPE is typically processed by ram extrusion or compression molding technique, but yet to be processed to the full potential of its mechanical integrity in acetabular shape without any fusion defects or weak bonding. The main objective of the present study is to develop a novel technique to fabricate defect-free acetabular cups with desired bearing characteristics and surface finish by sintering medical-grade UHMWPE GUR 1050 powder after its cold isostatic compaction with optimum processing parameters. Sintering kinetics of UHMWPE is studied comprehensively using a thermomechanical analyzer. The influence of compaction pressure, sintering temperature, and sintering duration on sintering kinetics of UHMWPE is explored to realize their optimum. The optimally processed UHMWPE has the relative density of 97% and Vickers hardness of 5.4 with tensile yield strength and elastic modulus of 21.5 and 625 MPa, respectively. The newly developed acetabular cup exhibited inherent plateau-finished bearing surface with an average surface roughness of <100 nm, having good bearing characteristics and desired dimension.     

Effect of CNT dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/Al joints

The tensile and shear strengths of adhesively bonded aluminum (Al) joints were inspected in the presence of amino functionalized multi-wall carbon nanotubes (MWCNTs). Tensile and shear tests were carried out using butt and lap-shear joints. The main goal was to compare the effects of dispersion methods of functionalized-CNT into epoxy on the mechanical performances and failure mechanisms of Al joints. Two different types of dispersion procedures, distributing CNT in the hardener (HH method) and distributing CNT in the resin (RR method), were applied. To identify the failure mechanisms, the morphology of fracture surfaces were analyzed using scanning electron microscopy (SEM). Comparing two dispersion methods against one another ascertained that following the RR method for dispersing CNTs in the adhesive displayed larger shear strength, while applying HH method offered fairly greater tensile strength. Moreover, dispersing CNTs in the resin induced more uniform dispersion of CNTs as compared to distributing nanofillers in the hardener. Following RR method, CNTs good dispersion as well as the presence of effective crack growth dissipating mechanisms, increased the shear strength of CNT reinforced adhesive joint. Incorporating CNTs using HH approach encouraged the plastic void formation of epoxy around the agglomerated CNTs, and as a consequence, promoted the plastic deformation under tension.     

Freeze‐drying method prepared UHMWPE/CNTs composites with optimized micromorphologies and improved tribological performance

Uniformly dispersed carbon nanotubes (CNTs) reinforced ultrahigh molecular weight polyethylene (UHMWPE) composites were successfully prepared by freeze‐drying method. Specifically, polymer powders were mixed with CNT aqueous paste, and then freeze‐dried. As a consequence, CNTs covered at the surface of UHMWPE powders evenly when CNT content was not very high, which improved the quantity of crystals and crystallinity of UHMWPE/CNTs composites by providing more nucleation sites during the upcoming compression‐molded process. Furthermore, optimized dispersion state of CNTs and concomitant higher crystallinity made freeze‐drying technique prepared composites display much lower wear rate when compared with pure UHMWPE and UHMWPE/CNTs composites fabricated by common heat‐drying method. In a word, our proposed method of freeze‐drying is simple and effective for mass production of UHMWPE/CNTs composites, and it is promising to be applied to fabricate many kinds of nanofillers modified polymer composites, for example, polymer/graphene material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41885.     

Effects of reinforcements and gamma-irradiation on wear performance of ultra-high molecular weight polyethylene as acetabular cup liner in hip-joint arthroplasty: A review

Improving the wear resistance of ultra-high molecular weight polyethylene (UHMWPE), the gold standard polymer for acetabular component in hip joint arthroplasty, is the most important challenge in joint arthroplasty. The possible ways that have been approached to this challenge are by: (i) engineering multi-phase that is, both carbonaceous and noncarbonaceous fillers-based polyethylene composites, which unite the inherent attributes of each element available in the system. The wear rate of carbonaceous composite is nearly 50% lower (5.11–6.69 × 10⁻⁵ mm³/Nm) than that of noncarbonaceous composite (10–12.5 × 10⁻⁵ mm³/Nm), thus, recognized as a potential reinforcement, and (ii) coupling gamma-irradiation, which is a mandated sterilization process, with multi-phase nanocomposite to understand the free radical-scavenging effect of fillers and improved interfacial adhesion strength between fillers and matrix. After the exposure of gamma-rays (50–100 kGy), the free radicals formed by bond breakage in both the reinforcements and the matrix recombine to form covalent/Van der Waals bond in the interface. Thus, dramatical improvement in wear resistance of both types of composites with 2–4 times decreased wear rate is observed compared to that of composites under un-irradiated condition. However, enhancing the interfacial adhesion between two different phases is a major constraint in the design of UHMWPE composites. Many methods such as functionalization of reinforcements, and irradiation on functionalized UHMWPE composites that can be approached to address this constraint are documented in this review.     

Wear resistant UHMWPE with high toughness by high temperature melting and subsequent radiation cross-linking

The goal of this study was to create wear resistant ultra high molecular weight polyethylene (UHMWPE) with improved strength and toughness. It was previously demonstrated that high temperature melting (HTM) of UHMWPE at 280-320 °C improved its toughness without detrimentally affecting its wear resistance. We hypothesized that radiation cross-linking after high temperature melting could further improve the wear resistance of UHMWPE, and the loss in toughness by radiation cross-linking could be compensated by the improved toughness achieved by the high temperature melting prior to irradiation. In this work, we demonstrated that irradiation after HTM generated UHMWPE with improved toughness compared to the irradiated UHMWPEs without HTM, partly due to the low cross-link density of irradiated HTM UHMWPE. At a given cross-link density, irradiated HTM UHMWPEs showed higher wear resistance than irradiated UHMWPE. Therefore, successive HTM and radiation cross-linking strategy is promising to create UHMWPE materials with low wear and improved mechanical properties for total joint implants.     

Advanced ultra‐high molecular weight polyethylene/antioxidant‐functionalized carbon nanotubes nanocomposites with improved thermo‐oxidative resistance

Multiwalled carbon nanotubes (CNTs) functionalized with hindered phenol moieties are dispersed in ultra‐high molecular weight polyethylene (UHMWPE), and the stabilizing action of the antioxidant (AO) functionalized CNTs (AO‐f‐CNTs) is studied through a combination of rheological and spectroscopic (FT‐IR) analyses. The effectiveness of two alternative compounding methods, namely hot compaction (HC) and melt mixing (MM), is compared. The combination of high temperature and mechanical stress experienced during MM brings about noticeable degradation phenomena of the matrix already in the course of the compounding step. Differently, the milder conditions of the HC process preserve the stability of the polymer, making this method preferable when dealing with highly viscous matrices. In addition, HC guarantees a better CNT dispersion, allowing for the maximization of the stabilizing action of the AO grafted on the nanotubes. As a result, the HC samples exhibit improved thermo‐oxidative resistance despite the very low amount of AO grafted onto the CNTs. Besides demonstrating the effectiveness of our AO‐f‐CNTs as stabilizers for polymer matrices, our results prove that CNTs can serve as a support on which grafting specific functional molecules to be dispersed in a host polymer matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42420.     

Ultra high molecular weight polyethylene with improved plasticity and toughness by high temperature melting

Our goal was to improve the strength and toughness of ultra high molecular weight polyethylene (UHWMPE), which is the preferred polymeric bearing material in total joint implants. Based on accelerated diffusion of UHMWPE chains at high temperatures, our hypothesis was that high temperature melting could minimize the structural defects and thus improve the toughness of consolidated UHMWPE. Melting of consolidated medical-grade UHMWPE at 280, 300, and 320 °C in inert atmosphere improved the elongation at break, work-to-failure and impact strength, presumably due to chain scissioning and structural defect elimination through self-diffusion. An important finding of this study was that the gain in plasticity and toughness did not sacrifice the wear resistance under optimized melting conditions, which may be promising for next generation high performance UHMWPE materials for joint implant bearing surfaces.     

UV irradiation and aging effects on nanoscale mechanical properties of ultra high molecular weight polyethylene for biomedical implants

Abstract

As a result of its relatively high strength, high chemical resistance, low creep and low wear rate, ultra high molecular weight polyethylene (UHMWPE) has been widely used as the 'soft' articulating surface for total hip and knee arthroplasty. However, for long term artificial joint replacements, accelerated wear as a result of aging of UHMWPE is one of the most important problems that can lead to joint failure. Therefore, the present work is focused on investigating the effects of thermal and serum aging and UV irradiation dose on the nanomechanical properties (elastic modulus, hardness and visco-elasticity) of UHMWPE (type GUR410) specimens under different deformation rates. The continuous stiffness measurement (CSM) nanoindentation technique is used in the present work to measure the nanomechanical properties. The results show a considerable increase in the nanomechanical properties with increasing deformation rate. It is also demonstrated that the nanomechanical properties of the thermally and serum aged UHMWPE specimens decrease compared to the virgin specimens, while their visco-elastic behaviour increases. For the UV irradiated specimens, the nanohardness and nano-elastic modulus show an increase with irradiation dose especially for small penetration depths. Moreover, a considerable decrease in visco-elastic behaviour was observed for the UV irradiated specimens as a result of the crosslinking effect of the radiation.     

Effect of surface modification of Kevlar fibre on friction and wear properties of UHMWPE composites

Abstract

The effects of Kevlar fibre additions and, particularly, the surface modification of the Kevlar fibres, on the sliding wear behaviour of the ultra high molecular weight polyethylene (UHMWPE) composites were investigated. The results showed that the sliding friction coefficient of the UHMWPE composites increased with the fibre content increase. The wear resistance of the UHMWPE composite was highest when the Kevlar fibre content was ～10 vol.-% and decreased as the applied normal load was increased. It was found that the silane modification of the Kevlar fibres improved the wear resistance and tensile strength of the UHMWPE composites as well.     

Assessment of intertube interactions in different functionalized multiwalled carbon nanotubes incorporated in a phenoxy resin

In this work, about 1 wt% of different functionalized carbon nanotubes (CNTs), namely CNT? COOH (CNT with carboxylic groups), CNT? NH₂ (CNT with amine groups) and CNT? OH (CNT with hydroxyl groups), as well as nonfunctionalized CNTs were incorporated into a phenoxy resin via a melt mixing process. The extent of intertubes and polymer–tubes interactions and their influence on state of CNTs dispersion were assessed through determination of electrical, rheological, and morphological characteristics. CNT? NH₂ showed the lowest intertubes interactions followed by CNT? OH and CNT? COOH. Nanocomposite made from CNT? COOH showed the poorest state of CNTs dispersion and the biggest CNTs agglomerates and it remained nonconductive. The acid‐functionalized CNTs were not able to form strong polymer–tube interactions because of their high cohesive energy and therefore in the melt rheological investigations they exhibited the lowest storage modulus and complex viscosity as well as the highest loss factor among all the studied CNTs. A good balance between intertubes and polymer–tube interactions is necessary through proper selection of CNTs functional groups for achieving a good state of CNTs dispersion and consequently obtaining enhanced electrical and viscoelastic properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

High temperature melted,radiation cross-linked,vitamin E stabilized oxidation resistant UHMWPE with low wear and high impact strength

In a previous communication we showed improvement in the wear resistance and toughness of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) for total joint implants by radiation cross-linking after high temperature melting (HTM). In this study, we hypothesized that introduction of vitamin E into UHMWPE before high temperature melting could improve the oxidative stability of these UHMWPEs with low wear and high toughness. Vitamin E was blended with UHMWPE powder at concentrations of 0.1 and 0.2 wt% and consolidated, followed by melting at 300 and 320 °C for 5 h, and subsequent irradiation with electron beam to 150 kGy. These vitamin E/UHMWPE blends showed improved tensile and impact toughness and good wear resistance in comparison with the radiation cross-linked vitamin E/UHMWPE blends. Aggressive accelerated aging with or without pro-oxidant lipids showed that vitamin E-blended, high temperature melted and subsequently irradiated UHMWPE had good oxidation resistance.     

Oxidation resistance and abrasive wear resistance of vitamin E stabilized radiation crosslinked ultra‐high molecular weight polyethylene

The effect of gamma radiation on the oxidation and wear resistance of ultra‐high molecular weight polyethylene (UHMWPE) has been extensively studied since these properties are critical for the longevity of UHMWPE components of total joint replacement prostheses. While gamma radiation increases wear resistance of UHMWPE, the free radical generated in the lamellar regions by radiation must be stabilized before oxidative degradation occurs as the polymer ages. Initially, post‐radiation melting conducted to quench free radicals but this treatment also decreases its mechanical properties. Recently, it has been replaced by incorporation of Vitamin E into UHMWPE to combat oxidative degradation. In this study, we assessed wear resistance of Vitamin E stabilized UHMWPE under abrasive wear conditions and oxidation resistance by shelf‐aging irradiated components for 2 years. Equilibrium swelling experiments showed that Vitamin E decreased crosslink density, which affected wear resistance, but oxidation resistance was better preserved with increasing concentration of Vitamin E. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44125.     

纳米TiO2-超高分子量聚乙烯复合材料的摩擦学特性

利用MM-200型摩擦磨损实验机,考察了纳米TiO2增强超高分子量聚乙烯（UHMWPE）复合材料在生理盐水润滑下,与Co—Cr—Mo合金对摩时的摩擦磨损性能,用光学显微镜观察了材料摩擦表面磨痕形貌。结果表明,适当填充纳米TiO2可提高UHMWPE的硬度,显著降低摩擦系数,增强耐磨性。UHMWPE的磨损主要表现为粘着、犁沟及塑性变形,TiO2-UHMWPE复合材料的磨损表现为轻微疲劳磨损。     

纳米材料改性UHMWPE人工关节的研究进展

人工髋关节的最薄弱部分是由超高分子量聚乙烯(UHMWPE)组成的髋臼,要延长人工关节的整体使用期限,应从改良UHMWPE的性能入手。对国内外近5年针对碳基纳米材料及其他纳米材料对UHMWPE的填充改性研究成果进行了综述及展望。     

Surface modification of ultra‐high‐molecular‐weight polyethylene. II. Effect on the physicomechanical and tribological properties of ultra‐high‐molecular‐weight polyethylene/poly(ethylene terephthalate) composites

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching, with the aim of improving the performance of its composites with poly(ethylene terephthalate) (PET) fibers. In this article, we report on the morphology and physicomechanical and tribological properties of modified UHMWPE/PET composites. Composites containing chemically modified UHMWPE had higher impact properties than those based on unmodified UHMWPE because of improved interfacial bonding between the polymer matrix and the fibers and better dispersion of the fibers within the modified UHMWPE matrix. Chemical modification of UHMWPE before the introduction of PET fibers resulted in composites exhibiting improved wear resistance compared to the base material and compared to unmodified UHMWPE/PET composites. On the basis of the morphological studies of worn samples, microploughing and fatigue failure associated with microcracking were identified as the principle wear mechanisms. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006