Mechanical Properties Of Ultra-high Molecular Weight Polyethylene Research Articles

Polymer Physics behind the Gel-Spinning of UHMWPE Fibers.

Gel-spinning of ultra-high molecular weight polyethylene (UHMWPE) fibers has attracted great interest in academia and industry since its birth and commercialization in the 1980s, due to unique properties such as high modulus, low density, and excellent chemical resistance. However, the high viscosity and long relaxation time greatly complicate processing. In industry, solvents, like decalin and paraffin oil, usually disentangle the physical networks and promote final drawability. From extruding the polymer solution to post-solid-stretching, many polymer physics problems that accompany high-modulus fiber gel-spinning should be understood and addressed. In this review, by detailed discussions about the effect of entanglements and intracrystalline chain dynamics on the mechanical properties of UHMWPE, theoretical descriptions of the structure formation of disentangled UHMWPE crystals, and the origin of high modulus and strength of final fibers are provided. Several physical intrinsic key factors are also discussed, revealing why UHMWPE is an ideal material for producing high-performance fibers.

The Simulation of Ultra-High Molecular Weight Polyethylene Cryogenic Pipeline Stress-Strain State

At present the production of polymer materials is developing intensively, new materials, comparable with steels in their strength properties have recently appeared. In this connection, the analysis of polymer materials applied in the pipe industry has been carried out, and the use of ultra-high molecular weight polyethylene (UHMWPE) is proposed as a structural pipeline material, allowing pipes to operate at cryogenic temperatures. The focal point of the article is the consideration of the fracture mechanisms of those materials and the nature of the change in the mechanical properties of UHMWPE under cryogenic temperatures, also taking into account the creep process. The expression for determining the value of the creep modulus depending on the temperature and operating time was obtained. A method is proposed for conducting initial strength estimation. Moreover, the computer model of stress-strain state of an underground cryogenic polymer pipeline for liquefied natural gas transportation is obtained. The results of simulation depict the potential possibility of using of UHMWPE for the cryogenic pipeline construction

Tribological and mechanical behaviors of mollusk shell‐ultrahigh molecular weight polyethylene bio‐composite

AbstractThis work is focused on the study of the tribological and mechanical properties of mollusk shell (MS)‐ultrahigh molecular weight polyethylene (UHMWPE) biocomposite against stainless steel. Wear tests were carried out on a reciprocating pin on disc apparatus. Tensile tests were achieved using a computerized universal traction machine, model EZ‐20 LLOYD. Rockwell hardness of the bio‐reinforced composite was carried out using an AFFRI universal hardness test. The coefficient of friction and wear rate were measured after tribological tests. From tensile tests, the ultimate strength, Young's modulus, fracture strain, and fracture strength were determined. It is found that wear tests of MS‐UHMWPE biocomposites achieved high tribological performance in terms of specific wear rate and coefficient of friction compared to pure UHMWPE. The mechanical properties of UHMWPE were enhanced by the addition of MS particles. The correlation between the mechanical and tribological properties of MS‐UHMWPE biocomposites was investigated. It is established that there is no solid confirmation of a strong correlation between the mechanical properties and the specific wear rate of MS‐UHMWPE biocomposites. However, the coefficient of friction gives a reasonable correlation with the hardness, fracture strain, fracture strength, and Young's modulus of the MS‐UHMWPE.

UHMWPE / nanodiamond nanocomposites for orthopaedic applications: A novel sandwich configuration based approach

Ultra high molecular weight polyethylene (UHMWPE) remains a primary choice of material for load bearing applications in total joint arthroplasty. Superior mechanical properties and wear resistance are unique to its performance. However, the addition of nanomaterials has improved its properties significantly. In the present study, a novel sandwich configuration has been considered to achieve unique surface and bulk properties specific to these sandwich composites. UHMWPE was reinforced at various loadings of 0.1, 0.3, 0.5, and 0.7 wt. % by surface modified Nano-diamond (ND). It is observed that the young's modulus, yield stress, fracture stress and toughness of UHMWPE were improved by 15, 31, 30, and 49.6% respectively at the optimum loading of 0.5 wt. % ND filler. The % of elongations and impact strength showed best results at 0.3 wt. % ND. Sandwich nanocomposites were prepared with the optimum loading of 0.3 & 0.5 wt. % ND and assessed for their properties and behaviour. The sectional hardness of sandwich nanocomposites revealed the cross-sectional variation of properties of the material. The reasons for diminution of the mechanical properties of nanocomposites and sandwich nanocomposites were also ascertained by rheological studies. The vibration response, damping behaviour, water contact angle and density of the composites which influence the longevity of the implant material were also assessed. The sandwich composite (PE 0.3ND - PE - PE 0.3ND) has shown better performance in all respect as compare to SW1 and SW3 composite due to good intermingling between the adjacent layers. It is concluded that the existence of ND improved the surface properties and mechanical properties of UHMWPE. However, sandwich nanocomposites have shown better properties unique unto itself.

Effect of Supercritical Carbon Dioxide on Dyeability and Physical Properties of Ultra-High-Molecular-Weight Polyethylene Fiber

Abstract Supercritical carbon dioxide dyeing, a new type of anhydrous dyeing method, has a lot of advantages, mainly conservation of energy, prevention of pollution, reusability of dye, and many more. This study presents a viable method for the dyeing of an ultra-high-molecular-weight polyethylene (UHMWPE) fabric by using supercritical carbon dioxide (scCO2) as a medium. Five hydrozono propanenitrile dyes that are functional colorants having antibacterial activity were applied for the dyeing of the UHMWPE fabric in scCO2 at a pressure of 20 MPa and at temperature of 120°C. The dyeability of UHMWPE fabric under scCO2 was evaluated by color measurement, whereby the color strength K/S was calculated. As the treating time and concentration of dye increased, the dyeability of the UHMWPE fabric displayed the tendency to continually improve. As decaline was added into scCO2 as the cosolvent, we obtained higher K/S. Furthermore, color fastness to rubbing and sublimation of the dyed UHMWPE fabric were determined according to Japanese Industrial Standards (JIS) L 0849 2 and JIS L 0854, and the trend showed that the increase in fastness corresponded to the increase in duration of the treatment. The influence of scCO2 dyeing on the mechanical properties of UHMWPE was also examined. Consequently, it was found that dyeing in scCO2 containing decaline reduced the crystallinity of the UHMWPE fabric and the breaking strength decreased. The antimicrobial property of UHMWPE dyed with N′-(2-chloro-4-methylphenyl)-2-oxo-2-(p-tolyl)acetohydrazonoyl cyanide was tested against three different microorganisms, and the results have been reported.

Rheological and mechanical properties of ultrahigh molecular weight polyethylene/high density polyethylene/polyethylene glycol blends

Abstract Ultra-high molecular weight polyethylene (UHMWPE) possesses many excellent properties, but poor processability. There are many ways to improve the processability of UHMWPE, but most of which will compromise its other outstanding properties. The effect of polyethylene glycol (PEG) and high-density polyethylene (HDPE) on the rheological and mechanical properties of UHMWPE were investigated in this paper, and the UHMWPE blends were prepared by twin screw extruder. The addition of PEG can remarkably improve the processability of UHMWPE, so the UHMWPE/PEG (100/4) blends can be steadily extruded from the capillary. In addition, the apparent shear viscosity, storage modulus, loss modulus and the complex viscosity decrease with the increasing amount of PEG. However, the mechanical properties of UHMWPE/PEG blends decrease as the PEG content increase. The incorporation of HDPE can further improve the processability of the UHMWPE/PEG blends and reduce its apparent shear viscosity, storage modulus, loss modulus and complex viscosity. Mechanical properties test reveals that the best ratio of UHMWPE/HDPE is 60/40. Compared with UHMWPE/PEG (100/4), the tensile strength, flexural strength, and flexural modulus of UHMWPE/HDPE/PEG (60/40/4) increase by 13.8%, 25.7%, and 32.5%, respectively.

Titanium(III, IV)-Containing Catalytic Systems for Production of Ultrahigh Molecular Weight Polyethylene Nascent Reactor Powders, Suitable for Solventless Processing-Impact of Oxidation States of Transition Metal.

Catalytic systems containing TiCl4 or TiCl3, THF, organomagnesium (n-Bu2Mg) and organoaluminum compounds capable of producing ultrahigh molecular weight polyethylene (UHMWPE) were developed. The resulting polymers were characterized by a molecular weight in the range of (1.8–7.8) × 106 Da and desirable morphology, suitable for modern methods of polymer processing—the solvent-free solid-state processing of superhigh-strength (tensile strength up to 2.1 GPa) and high-modulus (elastic modulus up to 125 GPa) oriented films and film tapes. The impacts of a THF additive, the oxidation state of the titanium atom, and the composition and nature of the nontransition organometallic compounds on the formation of catalytic systems for UHMWPE production were evaluated. The results indicate the suitability of individual titanium chloride tetrahydrofuran complex application for the formation of THF-containing catalytic systems. This approach also results in a significant increase in the system catalytic activity and mechanical properties of UHMWPE. The catalysts based on Ti(III) were inferior to systems containing Ti(IV) in productivity but were markedly superior in the mechanical properties of UHMWPE.

The effect of irradiation surface treatment of UHMWPE fibre on the interfacial properties of PVC composite

ABSTRACTIrradiation surface modification method was used for the surface treatment of ultrahigh molecular weight polyethylene (UHMWPE) fibre to improve the interfacial adhesion of the UHMWPE fibre reinforced PVC composite. The surface characteristics of untreated and treated UHMWPE fibre were characterised by XPS and Fourier transform infra-red spectroscope. The friction and wear properties of the PVC composites filled with differently surface-treated UHMWPE fibres (20 vol.-%), were investigated on a ring-on-block tribometer. Experimental results revealed that irradiation treatment largely increased the mechanical properties of UHMWPE fibre/neoprene/PVC (UF/N/PVC) composites. Scanning electron microscope investigation of worn surfaces of PVC composites showed that surface-treated UF/N/PVC composite had the strongest interfacial adhesion.

Impact of lipid-induced degradation on the mechanical properties of ultra-high molecular weight polyethylene for joint replacements

Gamma or electron beam irradiation of ultra-high molecular weight polyethylene (UHMWPE) used in artificial joints for sterilization and/or crosslinking purposes generates free radicals in the material, which causes long-term oxidative degradation of UHMWPE. Recently, another mechanism for the degradation of UHMWPE by the absorption of lipids during in vivo clinical use was proposed. However, knowledge on lipid-induced degradation is quite limited, compared with that on radical-induced degradation. In this study, lipid-induced degradation was simulated using squalene absorption and subsequent accelerated aging, and its impact on the mechanical properties of UHMWPE was evaluated. The simulated lipid-induced degradation caused an increased elastic modulus and decreased elongation with maximum degradation at the surfaces. These results imply that degradation of UHMWPE may occur during in vivo long-term use, even if free radicals are completely eliminated. Therefore, further investigation is required to clarify the impact of lipid-induced degradation on clinical outcomes, such as the wear and fatigue characteristics of UHMWPE components.

Mechanics of ZnO micro-rod and ZnO nanoparticle reinforcement in ultra-high molecular weight polyethylene biocomposite

Ultra-high molecular weight polyethylene (UHMWPE) is one of the most promising materials for cartilage replacement as an acetabular cup liner. Implant failure due to infection is a serious issue and ZnO is a well-known antibacterial agent. In the current work, the effect of the morphology of ZnO on the mechanical properties of UHMWPE is studied, where ZnO is incorporated both as nanoparticles (ZnO(NP)) and micro-rods (ZnO(R)) at 5, 10, 15 and 20 wt%. Uniaxial tensile testing of compression-moulded composites elicited a decrease of 8.8% in the Young's modulus in UHMWPE-ZnO(R) (named ZnO(R)-PE), whereas an increase of 21.1% in the Young's modulus was observed for UHMWPE-ZnO(NP) (named ZnO(NP)-PE). This contrasting effect on the Young's modulus arising due to differences in ZnO morphology is discussed and analysed using the rule of mixture and the Halpin–Tsai equation. Even when accounting for inherent porosity, and with similar crystallinity to that of base UHMWPE, these models fail to explain the decrease in the Young's modulus of compression-moulded ZnO-PE composites. Estimation of Young's modulus via a modified geometric factor is followed by proposing an empirical relation to account for interfacial strength and narrow the bounds of the predicted elastic modulus, thus making the Halpin–Tsai estimations reach the actual experimental values.

Positron Lifetime Studies of Irradiated Ultra-High Molecular Weight Polyethylene and Composites Made of Martian Regolith

Positron Annihilation Lifetime Spectroscopy (PALS) is used to study the nanoporosity and fractional free volume in Ultra High Molecular Weight Polyethylene (UHMWPE) and composites with the addition of Martian Regolith (UHMWPE-MR) as-made and irradiated with 56Fe heavy ions at an energy of 600 MeV/u to three different doses (10, 32, 64 Gy). The positron lifetime spectra were obtained using 22Na positron source and the spectra were analyzed to two lifetime components using POSFIT program. First short lifetime component around 0.28 ns is related to positron annihilation in material including vacancy defects and the second long lived component around 1.7 ns is due to Positronium formation in free volume pores. UHMWPE-MR composites were shown to be less porous with much lower nanopores concentration compared to the UHMWPE polymer. The average size of the nanopores is around 0.5 nm (obtained from a simple model). Larger variations in positron lifetime parameters are observed with increasing irradiation dose for UHMWPE polymer compared to UHMWPE+MR composites. The 3-point bend test results also showed larger variations with increasing irradiation dose for the UHMWPE polymer. The variations in PALS parameters may indicate an increasing competition between two processes at higher irradiation doses: 1) vacancy defects aggregation and 2) escape of vacancy defects as the local temperature increases at higher doses resulting in increased vacancy defects mobility. Present results clearly indicate a qualitative inverse relationship between nanoscale porosity measured by positron life time and mechanical properties of UHMWPE and its composite with MR.

The Design and Fabrication of Dimples Pattern on the Surface of UHMWPE

Tribological problems are the major obstacle that limits the long-term using of ultra high molecular weight polyethylene (UHMWPE) in artificial joints. Many efforts have been made to improve the tribological properties of UHMWPE mainly by promoting the structure, morphology and mechanical properties of UHMWPE. In this paper, inspired from the natural joint, the micro-scale texture has been introduced to improve the tribological properties of UHMWPE. The micro-imprint lithography technology has been adopted to fabricate the textured UHMWPE. The profile of textured UHMWPE shows that the quality of textured UHMWPE is good. The result of tribological tests shows that the micro-scaled surface texture can remarkably reduce friction on UHMWPE.

Effect of high‐energy ball milling on the structure and mechanical properties of ultra‐high molecular weight polyethylene

ABSTRACTThe structure and properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) powder after severe deformation processing in a planetary ball mill were studied by means of scanning electron microscopy, differential scanning calorimetry, and X‐ray analysis. We found that the severe deformation processing of UHMWPE changed the morphology of the powder and caused amorphization and partial changes in the structure of the crystalline phase. Monolithic samples were obtained from the pretreated polymer with a hot‐pressing method in a wide range of temperatures. The effect of preliminary deformation processing on the mechanical properties of UHMWPE was studied. It was revealed that during monolitization in its melting temperature range, the mechanical properties of the powder increased, whereas the percentage elongation decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2971–2977, 2013

Effect of adding polysilane on melt‐flow properties of ultra‐high molecular weight PE

AbstractThe effects of polysilane addition on the melt‐flow and mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) were investigated. The kneading torque during melt process of pure UHMWPE without polysilane increased significantly with time and reached a constant value after 100 min. However, the kneading torque did not increase by addition of polysilane materials into UHMWPE, which indicates that all the polysilane materials suppress an increase in the kneading torque during melt process of UHMWPE at 200°C, especially a linear polysilane (PMPS) and a networked structure polysilane (PPSi). When using linear polysilane materials with different molecular weights, the low molecular weight polysilane (PM‐5, Mw = 500 Da) had the most dominant effect on the heat‐flow and mechanical properties of UHMWPE. UHMWPE with PM‐5 could be elongated over 1000% strain, which was the similar to the case for pure UHMWPE, although the elongation at break of UHMWPE with additions of different molecular weight PMPS was significantly decreased with increasing molecular weight of PMPS. Furthermore, the kneading torque during melt process of UHMWPE decreased with increase in the amount of PM‐5 addition, from 1 to 5 wt %. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influence of different sterilization procedures on the morphological parameters and mechanical properties of ultra‐high‐molecular‐weight polyethylene

AbstractThe objectives of this study were to examine the effects of the processing conditions, sterilization, and thermal treatment on the morphological and mechanical properties of ultra‐high‐molecular‐weight polyethylene (UHMWPE) in medical applications by means of thermal analysis, Fourier transform infrared spectroscopy, and nanoindentation. It is well known that manufacturing, irradiation, and thermal treatments significantly alter the microstructure of materials, which results in changes in their mechanical properties. UHMWPE was found to be barely sensitive to processing conditions but strongly influenced by sterilization treatments. Great emphasis was given to the characterization of the so‐called first generation of highly crosslinked UHMWPE because the thermal history of this material differed from that of γ‐irradiated materials. The physical and mechanical properties of UHMWPE were influenced as a result of γ and electron‐beam irradiation and the remelting procedure. Lower crystallinity, different lamellar thickness distributions, and lower hardness and modulus values were estimated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Analysis of the essential work of fracture method as applied to UHMWPE

The validity of the basic assumptions behind the method of essential work of fracture (EWF), as applied to ultra-high molecular weight polyethylene (UHMWPE), is evaluated using finite element modelling. To define a suitable model of constitutive behaviour, the mechanical properties of UHMWPE have been measured in both uniaxial tension and compression over a range of strain rates. The observed strain rate dependence of stress, including the observed differences in strain rate sensitivity between tension and compression, is interpreted in terms of a single Eyring process. The constitutive theory is constructed comprising an Eyring process and hyperelastic networks, the latter having responses symmetric with respect to tension and compression. This theory is implemented within a finite element scheme, and used to model fracture measurements made on the same material using double-edge notch tensile specimens. Calculations of the non-essential work and of the extent of the plastic zones are thus made possible. It is concluded that the specific non-essential work is essentially constant, but that the shape factor β, assumed constant in the conventional analysis, varies significantly with ligament length. The implication of this finding on the derived EWF value is evaluated and found to be slight.

The influence of injection molding on tribological characteristics of ultra-high molecular weight polyethylene under dry sliding

The objective of this study is to investigate the effects of various injection molding process parameters on the tribological properties of ultra-high molecular weight polyethylene (UHMWPE). The tribological properties, such as the friction coefficient and wear volume loss, were obtained using the Schwingum Reibung Verschleiss (SRV, oscillation friction wear) ball-on-plane wear tester. In addition, the mechanical properties of UHMWPE were investigated as well. The variable parameters of the injection molding process were melt temperature, mold temperature and injection velocity. Experimental results show that different wear contact loads and varied injection molding conditions influence the friction coefficient and wear volume loss of the UHMWPE specimens. As the sliding contact loads increased, the friction coefficient also increased. Moreover, the lowest wear volume loss mostly occurred in highest injection molding conditions. The morphologies of the worn surfaces and the specimen cross sections were examined with an optical microscope and a scanning electron microscope, respectively. Plastic deformations, grooves and wavelike formations are the main wear mechanism on the surface in the UHMWPE wear tests. Experimental results also showed that the tensile strength and surface hardness are affected by injection molding conditions and sliding contact loads.

Evaluation of sequentially crosslinked ultra‐high molecular weight polyethylene

This study was undertaken to investigate the effect of crosslinking ultra-high molecular weight polyethylene (UHMWPE) in a sequential manner to the final desired dose and to compare the results to single-dose crosslinking. To verify these results, an explanted, commercially available, sequentially crosslinked component was characterized. Finally, additional tensile testing was conducted to determine if tensile-sample thickness has a significant effect on the mechanical properties of UHMWPE. Based upon this well-controlled study with the same starting material, there is no apparent benefit of sequential crosslinking over crosslinking by single dose in any of the mechanical, thermophysical, physical, or oxidative properties evaluated in this study. In contrast, the soak temperature of the postirradiation heat treatment was more influential and exhibited statistically significant effects on the stability, structure, and properties of the resultant material. Compared to virgin material, crosslinking always resulted in decreases in tensile strength, elongation, and impact strength. These results were confirmed by characterization of a retrieved, sequentially crosslinked (X3) cup. All of the metrics derived for the retrieved cup were virtually identical to the sequential- and single-dose-crosslinked materials produced in this study. Examination of the effect of tensile-sample thickness demonstrated that there are significant effects on the resultant properties. In particular, the ultimate tensile strength of UHMWPE can be elevated by conducting tensile tests with thin specimens.

Crystalline Character and Microhardness of Gamma‐Irradiated and Thermally Treated UHMWPE

Relationships between Vickers microhardness, x‐ray and differential scanning calorimetry (DSC) crystallinity, x‐ray long period, and melting points were determined for ultrahigh molecular‐weight polyethylene (UHMWPE) of various histories (as‐produced, irradiated, annealed, and remelted). It was shown that the microhardness responds very sensitively to both the irradiation conditions (total radiation dose, radiation dose rate) and the thermal treatment (annealing below the melting temperature, remelting). As microhardness reflects the yield point parameters, the results show that not only the total dose, but also the irradiation dose rate has a considerable influence on mechanical properties of UHMWPE. It was demonstrated that neither x‐ray nor DSC results are so sensitive to treatment as the microhardness results. The most important differences in properties were found between remelted samples and those thermally untreated or annealed.

3311 超高分子量ポリエチレンの機械的特性に及ぼす環境劣化とVitamin-E添加の影響(S26-2 生体・環境適合材料の創製・強度評価技術開発2,S26 生体・環境適合材料の創製・強度評価技術開発)

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used for the bearing materials in joint arthroplasty owing to its superior mechanical properties and high chemical resistance. However, effects of gamma-irradiation and accelerated aging on the mechanical properties has not been revealed. In addition, although the addition of Vitamin-E to the gamma-irradiated UHMWPE has reported to prevent the fatigue crack propagation, the prevention mechanism has not been clarified yet. In order to understand the influence of gamma-irradiation, accelerated aging and Vitamin-E (α-Tocopherol) on the mechanical properties of UHMWPE, we carried out tensile test and fatigue test of UHMWPE fiber and fatigue crack growth tests of UHMWPE plates. For tensile test of fibers, the displacement at failure decreased by accelerated aging, but the decrease of displacement at failure was revealed by adding Vitamin-E. For fatigue test of fibers, virgin specimen was fractured at lower stress than tensile strength influenced by cyclic loading. Furthermore, the fatigue strength was lower for accelerated aging specimen than virgin one. For the fatigue crack growth behavior, addition of Vitamin-E reduced the decrease of ΔK_<th> by gamma-irradiation and accelerated aging.