Tribological Properties Of Ultra-high Molecular Weight Polyethylene Research Articles

Enhanced Tribological Performance of UHMWPE Composites Reinforced With Wollastonite: Biocompatibility and Wear Behavior

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is often limited by poor tribological properties in artificial joints, leading to high wear-rates compared to metals and ceramics. This study explores the use of wollastonite, a natural mineral, as a filler to enhance the tribological performance of UHMWPE composites. X-ray diffraction (XRD) analysis revealed that wollastonite content and particle size inversely affected the crystallinity of the composite due to heterogeneous nucleation and stress concentration. The incorporation of wollastonite significantly improved the tribological performance, with wear-rate reductions of 71%, 69.81%, and 50.73% under dry friction, normal saline (NS) lubricant, and new-born calf serum (NBCS) lubricant conditions, respectively. The wear mechanisms in the composite were predominantly slight fatigue and abrasive wear, contrasting with the extrusion deformation and severe fatigue wear observed in neat UHMWPE. Additionally, simulated body fluid (SBF) immersion tests demonstrated the composite's ability to form a surface apatite-like deposition. These findings suggest that wollastonite reinforcement effectively enhances both mechanical and tribological properties of UHMWPE.

Effects of Diffusing Squalene on the Plastic Deformation of Ultrahigh-Molecular-Weight Polyethylene─Insights from Molecular Dynamics Simulations.

Ultrahigh-molecular-weight polyethylene (UHMWPE) stands out as a popular artificial joint material. However, wear limits its service life, which is mainly caused by accumulation of plastic deformation. The plastic deformation on the frictional interface reflects the early wear of UHMWPE. To investigate the effect of squalene, a typical component in the body fluid, on the tribological properties of UHMWPE at microscopic scale, the diffusion behavior of squalene into polyethylene and its influence on the plastic deformation of polyethylene are discussed using the molecular dynamics (MD) simulation. The lubrication model shows that polyethylene reconstructed from the interface to lower substrate, with refactor gaps between polyethylene chains. This promotes squalene molecules to gradually diffuse into polyethylene from these gaps and causes the polyethylene structure to become loose. On the other hand, in the diffused model, squalene in polyethylene substrates increases the plastic deformation of polyethylene. The separation of squalene reduces the interaction strength between adjacent polyethylene chains and accelerates the disentanglement of polyethylene. The flexibility of "C═C" bonds in squalene allows the continuous adjustment of its spatial structures to adapt the space between polyethylene chains. The squalene fragments will not hinder the plastic flow of polyethylene.

Fabrication and tribological behavior of novel UHMWPE/vitamin-C/graphene nanoplatelets based hybrid composite for joint replacement

PurposeThis study aims to fabricate and investigate the tribological performance of ultra-high molecular weight polyethylene (UHMWPE)-based composite materials reinforced with 0.5, 1 and 2 weight percentage of graphene nanoplatelets (GNPs) while keeping the weight percentage of vitamin C constant at 2% for each composite.Design/methodology/approachIn this paper, the composites were fabricated using hot pressing, and the dispersion of GNP/vitamin C/UHMWPE hybrid composite was investigated by X-ray diffraction. Experimental trials were performed according to ASTM F732 on a reciprocating sliding tribometer (pin-on-disc) at human body temperature of 37 ± 1 °C, for a load of 52 N, to assess the role of these fillers on the tribological properties of UHMWPE against Ti6Al4V counter body material under dry and lubricating (human serum) environment.FindingsIn this study, it has been observed that friction and wear behavior of the developed composites improve with increase in weight percentage of GNP, and human serum adheres to the surface of the composite pins upon sliding, resulting in the formation of a film, which results in better wear resistance of the composite pins under human serum lubrication than dry sliding. Scanning electron microscope was used to investigate the worn surface morphological examination of the composite materials. Specific wear rate of 0.76 × 10−7 mm3/Nm was attained for 2 Wt.% GNP-filled composite under human serum lubrication.Practical implicationsThe results indicate the compatibility of the composite material used in this study and suggested the in vitro implant application.Originality/valueThe presented work includes novel study of synergistic effect of GNP (which acts as a solid lubricant) and vitamin C (added as an antioxidant) on the tribological performance of UHMWPE under dry and human serum lubrication.

SiO2‐covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO2) nanocomposites with superior mechanical and tribological properties

ABSTRACTThe modified Hummer technique was used in the preparation of graphene oxide (GO) nanosheets, and then SiO2 decorated GO [GO(SiO2)] nanosheets were synthesized via the sol–gel method. Then, ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites loaded with 0.5, 1, 1.5, and 2 wt % of GO(SiO2) were prepared using magnesium ethoxide/GO(SiO2)‐supported Ziegler–Natta catalysts via the in situ polymerization. Morphological study of the prepared polymer powders was assessed using field‐emission scanning electron microscopy, which showed that GO(SiO2) nanohybrids have been uniformly dispersed and distributed into the UHMWPE matrix. Also, the neat UHMWPE and its nanocomposites were evaluated with different analyses, including viscosity‐average molecular weight measurement, differential scanning calorimetry, thermogravimetric analysis, tensile test, scratch hardness, and pin‐on‐disk test. The characterization of the UHMWPE nanocomposites indicated that many characterizations, including the mechanical, thermal, and tribological properties of UHMWPE, were significantly improved by incorporation of these new nanosheets in spite of the molecular weight reduction of the polymeric matrix and the improved flowability and processability of the produced nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47796.

Biodegradation behavior and tribological properties of ultrahigh molecular weight polyethylene stabilized with α-tocopherol

PurposeThis paper aims to investigate the effect of simulated body fluid (SBF) on biodegradation and tribological properties of ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE stabilized with α-tocopherol.Design/methodology/approachThe samples of UHMWPE and UHMWPE stabilized with α-tocopherol were prepared by a hot-pressing method, and then immersed in SBF for one year. Tribological test was performed on a UMT-2 tribometer.FindingsThe crystallinity and tribological properties increased slightly after UHMWPE stabilized with α-tocopherol, whereas the O/C ration decreased slightly. The crystallinity and O/C ratio increased after all samples immersed in SBF for one year. This resulted in the deterioration of tribological properties and the wear mechanism change. The tribological properties change was smaller in UHMWPE stabilized with α-tocopherol than that in UHMWPE, because the oxidation resistance of UHMWPE was increased by α-tocopherol.Originality/valueThe results of the experimental studies demonstrated and compared the biodegradation behavior and tribological properties of UHMWPE, UHMWPE stabilized with α-tocopherol, and after they immersed in SBF for one year.

Tribological behavior of aged UHMWPE under water-lubricated condition

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is commonly used to make water-lubricated bearing in industrial application. The Water-lubricated bearing components often experience boundary and mixed lubrication during operation, which induces the aging of UHMWPE material, affecting the mechanical and tribological properties of UHMWPE. This investigation aims to study how the wear resistance of UHMWPE is affected by aging. A CBZ-1 tribo-tester was used to conduct the sliding wear tests between UHMWPE pins and ZCuSn10Zn2 discs rubbing pair under water lubrication. The comparison analyses of the shore hardness, friction coefficients, wear mass loss and worn surface morphologies were elevated. Also, the Raman spectrum, Infrared spectrum and the change of elements of aged UHMWPE samples were examined. The results showed that the accelerated aging had a significant effect on the mechanical and tribological properties of UHMWPE. Especially, compared with the original sample the average friction coefficient increases by 65.96% under 720 h, 80 °C aging condition. Moreover, accelerated aging also resulted in a fracture of molecular chains and chemical oxidation reaction of UHMWPE, the concentration of O element increased to 12.803% when the aging condition was 720 h, 80 °C, which was closely correlated with the deterioration of its wear resistance. The main wear mechanisms were fatigue wear and abrasive when the aged temperature was 40 °C, 60 °C and the aged time was 120 h, 240 h and 360 h. At the 80 °C, 480 h and 720 h aged conditions, the main wear mechanisms between rubbing pair were adhesin wear and fatigue wear. The knowledge gained herein will be useful for optimizing and designing water-lubricated material in extreme conditions to prolong the service life of water-lubricated bearings.

Investigation and Optimization of Mechanical, Thermal and Tribological Properties of UHMWPE – Graphite Nanocomposites

The objective of this study is to investigate the influence of nano-sized graphite on the mechanical, thermal and wear characteristics of Ultra High Molecular Weight Polyethylene (UHMWPE) - Graphite (Nano 27) nanocomposites. Mechanical, wear and thermal properties were analyzed for nanocomposites containing 0.5, 1, 1.5 and 2% graphite and compared with unfilled UHMWPE. The wear properties of the nanocomposites were modeled and optimized for nano-graphite content and process parameters viz. sliding velocity and load. Response surface methodology (RSM) was utilized for modeling and optimization for reducing the wear rate in the nanocomposites. The degree of wear and the worn surfaces were evaluated by Field Emission Scanning Electron Microscope (FESEM).

A TRIBOLOGICAL ASSESSMENT OF UHMW POLYETHYLENE IN DRY AND LUBRICATED CONDITIONS

The aim of the study was to evaluate tribological properties of ultra-high-molecular-weight polyethylene (UHMWPE). This study concerns the areas of both mechanical and biomechanical application fields, including chain guides and knee or hip joint liner replacement. The presented paper describes conducted research on tribological properties of UHMWPE with tribological testing station UMT-2 Bruker. This testing station is capable of conducting tribological tests of ferrous, non-ferrous metals, plastics, ceramics, composites, and various types of coatings, under both "dry" and liquid and solid lubricating agents. Tests were performed under various conditions, differing in relative speed and the load of interacting frictional pair. Moreover, test duration and the performed number of cycles were considered.

The mechanical properties of the ultrahigh molecular weight polyethylene (UHMWPE) modified by oxygen plasma

In this work, ultrahigh molecular weight polyethylene (UHMWPE) was modified with oxygen plasma generated by microwave electron cyclotron resonance (ECR). Surface microstructure and properties of UHMWPE were studied by means of water contact angle measurement, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy, scratch test and wear test. The results showed that O 2 plasma treatment could effectively improve the wettability, anti-scratch and tribological properties of UHMWPE. Many oxygen-based functional groups generated on the surface of the O 2 plasma modified UHMWPE, which resulted in the improvement of wettability. The plasma treatment process increased the crosslinking of UHMWPE molecular chains, which further enhanced the action force between the molecular chains and finally increased the surface hardness, anti-scratch capacity and tribological properties of UHMWPE.

Study on Tribological Properties of Irradiated Crosslinking UHMWPE Nano-Composite

Ultra High Molecular Weight Polyethylene (UHMWPE) has been widely used as a bearing material for artificial joint replacement over forty years. It is usually crosslinked by gamma rays irradiation before its implantation into human body. In this study, UHMWPE and UHMWPE/nano-hydroxyapatite (n-HA) composite were prepared by vacuum hot-pressing method. The prepared materials were irradiated by gamma rays in vacuum and molten heat treated in vacuum just after irradiation. The effect of filling n-HA with gamma irradiation on tribological properties of UHMWPE was investigated by using friction and wear experimental machine (model MM-200) under deionized water lubrication. Micro-morphology of worn surface was observed by metallographic microscope. Contact angle and hardness of the materials were also measured. The results show that contact angle and hardness are changed by filling n-HA and gamma irradiation. Friction coefficient and wear rate under deionized water lubrication are reduced by filling n-HA. While friction coefficient is increased and wear rate is reduced significantly by gamma irradiation. The worn surface of unfilled material is mainly characterized as adhesive wear and abrasive wear, and that of n-HA filled material is mainly characterized as abrasive wear. After gamma irradiation, the degrees of adhesive and abrasive wear for unfilled material and abrasive wear of n-HA filled material are significantly reduced. Unfilled and filled materials after irradiation are mainly shown as slight fatigue wear. The results indicate that UHMWPE and UHMWPE/n-HA irradiated at the dose of 150 kGy can be used as bearing materials in artificial joints for its excellent wear resistance compared to original UHMWPE.