Ultra-high Molecular Polyethylene Research Articles

INFLUENCE OF NETWORK ON THE INTERFACIAL DIFFUSION OF MULTILAYER POLYETHYLENE BLENDS

Ultrahigh molecular mass polyethylene(UHMWPE) and statistical copolymer of ethylene and 1-hexene(PEH) were used to prepare UHMWPE/PEH blends with relatively low UHMWPE concentrations.UHMWPE forms network structure in the blends with UHMWPE concentrations above a critical value of c=1 wt%.The influence of the formed UHMWPE network on the interfacial diffusion behaviors of multilayer UHMWPE/PEH blends was investigated by applying small oscillatory shear rheology.The interfacial diffusion coefficients of multilayer UHMWPE/PEH blends were obtained from the rheological data.It is found that the diffusion coefficients are time-dependent and two diffusion regions are distinct before the diffusion reaches the plateaus according to the changes of diffusion exponent n in the relation of D-t n,which implies an approximate Fickian diffusion behavior in region Ⅰ(c 1.0 wt%) and an obvious deviation from the Fickian diffusion behavior in region Ⅱ(c1.0 wt%).With the formation of UHMWPE network in the UHMWPE/PEH blends,deviation from the Fickian behavior for diffusion of multilayer UHMWPE/PEH blends becomes significant.The above results help facilitate the industrial processing of multilayer polyolefins,which is related to the interfacial diffusion.

Microstructure, thermooxidation and mechanical behavior of a novel highly linear, vitamin E stabilized, UHMWPE

A novel, vitamin E-stabilized, medical grade ultra-high molecular polyethylene, MG003 (DSM Biomedical; The Netherlands), has been very recently introduced for use in total joint replacements. This homopolymer resin features average molecular weight similar to that of conventional GUR 1050 resin (5.5–6*106g/mol), but a higher degree of linearity. The aim of this study was to characterize the microstructure, thermal and thermooxidation properties as well as the mechanical behavior of this novel MG003 resin before and after gamma irradiation in air to 90kGy. For this purpose, a combination of experimental techniques were performed including differential scanning calorimetry (DSC), thermogravimetry (TG), transmission electron microscopy (TEM), X-Ray Diffraction, electron paramagnetic resonance (EPR), and uniaxial tensile tests. As-consolidated MG003 materials exhibited higher crystalline contents (~62%), transition temperatures (~140°C), crystal thickness (~36nm), yield stress (~25MPa) and elastic modulus (~400MPa) than GUR 1050 controls (55%, 136°C, 27nm, 19MPa, and 353MPa, respectively). Irradiation produced similar changes in both MG003 and GUR 1050 materials, specifically increased crystallinity (63% and 60%, respectively), crystal thickness (39nm and 30nm), yield stress (27MPa and 21MPa), but, above of all, loss of elongation to breakage (down to 442 and 469%, respectively). Thermogravimetric and EPR results suggest comparable susceptibilities to oxidation for both MG003 and GUR 1050 polyethylenes. Based on the present findings, MG003 appears as a promising alternative medical grade polyethylene and it may satisfactorily contribute to the performance of total joint replacements.

Preparing CNT/UHMWPE Composite and it’s Electrical Property Study

Composite particles with ultra-high molecular polyethylene (UHMWPE) core and carbon nanotube (CNT) shell were produced by an impact coating process, and molded into conductive polymer composites. Morphology of these composite particles was observed and the electrical behavior of these molded composites was measured. UHMWPE particles were very well coated by CNT, and conductive networks of CNT were formed after molding. These conductive polymer composites with low loadings of conductive filler exhibit lower room-temperature resistivity, and volume resistivity decreases with temperature on the whole. This is because of the CNT distribution is uniform in a macroscopic view but is oriented in a mesoscopic view. Thermionic emission of CNT is strong in polymer composites produced by this process. A related mechanism is discussed.

Failure analysis of retrieved UHMWPE tibial insert in total knee replacement

This study involves the failure analysis of an ultra high molecular polyethylene (UHMWPE) tibial insert from Apollo® Total Knee System, which was removed after 10 years of service from 70 years old female patient. The tibial insert was investigated by using a stereoscope, scanning electron microscope (SEM), infinite focus microscope (IFM) and energy disperse spectroscopy (EDS) to characterize the morphology and composition of the bearing surface. Differential scanning calorimetry (DSC) and Fourier transform spectroscopy (FTIR) were employed to characterize the degradation and crystallinity of the component. Gel-permeation chromatography (GPC) was used to measure the polyethylene tibial insert molecular weight. Results showed that the failure of total knee replacement (TKR) was associated with high grade wear and oxidation degradation. Surface delamination, scratch marks, pitting, folding, and embedded third body particles were observed on the retrieved UHMWPE tibial surface. Pit depth as large as 60 μm was measured on the surface. The damage features observed on the UHMWPE tibial insert suggested degradation is due to fatigue related wear and is oxidation-induced. Overall results show that the UHMWPE tibial insert which was retrieved from a patient who is active and but not overweight underwent degradation of material properties and high grade wear during 10 years of service.

Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions

A ternary blend of the bisiminopyridine chromium (III) (Cr-1) with the bisiminopyridine iron (II) (Fe-2) post-metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr-3) was supported on mesoporous silica to produce novel multiple single-site catalysts and polyethylene reactor blends with tailor-made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO-treated silica was Fe-2 followed by Cr-1 and Cr-3. Cosupporting does not impair the single-site nature of the blend components producing polyethylene fractions with $\overline M _{\rm w}$ = 10(4) g · mol(-1) on Cr-1, $\overline M _{\rm w}$ = 3 × 10(5) g · mol(-1) on Fe-2, and $\overline M _{\rm w}$ = 3 × 10(6) g · mol(-1) on Cr-3. As a function of the Fe-2/Cr-1/Cr-2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor-made polyethylene reactor blends with ultra-broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe-2/Cr-1 was constant, the ultra-high molecular polyethylene (UHMWPE, $\overline M _{\rm w}$ > 10(6) g · mol(-1) ) content was varied between 8 and 16 wt.-% as a function of the Cr-3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe-2/Cr-3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr-1. Due to the intimate mixing of low and ultra-high molecular weight polyethylenes (UHMPEs) produced on cosupported single-site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

Elaboration and realisation of innovative projects by “Tomskneftekhim” Ltd. and Institute of Catalysis of SB RAS in frames of special economic zone

The history of innovative projects creation for potential resident of SEZ started in 2005 when the Tomsk Oblast Governor V.M. Kress addressed the President of “AK” “SIBUR” OJSC, A.V. Dyukov a request to consider the prospects of allocation of the implementational Company divisions on the territory of SEZ and, in case of positive decision, to participate with the Administration of Oblast in preparation of regions to a competition on obtaining the right of creation of technical promotional type of SEZ on its own territory. Giving a consent, the President of the Company requested to include “Tomskneftekhim” Ltd. in the list of SEZ potential residents with two innovative projects, elaborated together with the Institute of Catalysys of SO RAN. These projects include: 1. Production technology elaboration of ultrahigh molecular polyethylene (UHMPE). 2. The creation of pilot plant and elaboration of processing for production of modern high effective catalysts for polypropylene and high density polyethylene manufacture. These projects are based on the use of highly effective titanium magnesium supported catalysts elaborated by Institute of Catalysis of SO RAN. The preparation method of these catalysts allows production of different modifi cations of these catalysts in frames of unifi ed technological scheme, which can be used for obtaining various polyolefi ns (UHMPE, polypropylene, high density polyethylene). “Tomskneftekhim” Ltd. was committed to prepare business plans and other documents necessary for running technical implementational activity in SEZ agreement. In December 2005 Tomsk Oblast won the competition on creation of implementation SEZ. “SIBUR” Ltd. fi nances the site reconstruction and innovative projects of “Tomskneftelhim” Ltd. and Institute of Catalysis (IC) with the support of Rosnauka (State contract No 02.431.11.7003). By present “SIBUR” Ltd. built on this site corporate scientifi c center “NIOST” Ltd. specializing on polymers and rubbers, which became the best equipped and staffed in the country. Objectively, only “SIBUT” Ltd. among Russian petrochemical companies is currently engaged in the development of Russian catalyst and polymerization technologies for the future application.

An activated energy approach for accelerated testing of the deformation of UHMWPE in artificial joints

The deformation behavior of ultrahigh molecular polyethylene (UHMWPE) is studied in the temperature range of 23–80 °C. Samples are examined in quasi-static compression, tensile and creep tests to determine the accelerated deformation of UHMWPE at elevated temperatures. The deformation mechanisms under compression load can be described by one strain rate and temperature dependent Eyring process. The activation energy and volume of that process do not change between 23 °C and 50 °C. This suggests that the deformation mechanism under compression remains stable within this temperature range. Tribological tests are conducted to transfer this activated energy approach to the deformation behavior under loading typical for artificial knee joints. While this approach does not cover the wear mechanisms close to the surface, testing at higher temperatures is shown to have a significant potential to reduce the testing time for lifetime predictions in terms of the macroscopic creep and deformation behavior of artificial joints.

Microstructural Investigation of Gamma-Irradiated Ultra High Molecular Weight Polyethylene in Nitrogen Atmosphere

In this paper the results of structural changes in ultra high molecular polyethylene (UHMWPE) upon gamma irradiation and storage in nitrogen environment are reported. Based on differential scanning calorimetry (DSC), wide angle x-ray scattering (WAXS), gel content, fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM), we show that upon gamma irradiation crystallinity percentage increases by 20% at high doses due to aging, at low doses up to 50 kGy there is no significant changes. Lamellar thickness increases with the dose, possibly due to chain scission and the addition of new molecular segments to the lamellae. Upon storage in nitrogen DSC data confirmed the appearance of new smaller lamellae. Crosslinking was achieved by irradiation but the ratio of scission to crosslinking is higher after aging. This was confirmed by the increase in the oxidation index and the high brittle behavior of the polymer after aging where fibrous surface was noticed.

Study on long life of artificial joints by investigating optimal sliding surface geometry for improvement in wear resistance

The effective life of artificial joints is approximately 15 years. A smooth metal sliding surface is presumably the most suitable when manufacturing artificial joints; however, the relationship between the characteristics of metal sliding surface and ultra high molecular polyethylene (UHMWPE) wear has not been confirmed. Further, there is no apparent proof that a smooth surface is the optimal option for the improvement in the wear resistance of artificial joints. In this study, we investigated the mechanism of UHMWPE wear and proved that scratch marks caused by a sliding motion against the metal surface are the prime cause of UHMWPE wear. Furthermore, we used a micro-dimpled surface as an effective sliding surface to reduce the UHMWPE wear. A 2-axes pin-on-plate sliding test proved that the life of artificial joints can be extended to approximately 35 years by using a micro-dimpled surface with 1-μm deep dimples.

Effect of an UHMWPE patellar component on stress fields in the patella: a finite element analysis

An increased stress in the patella due to the implantation of a patellar button may also be another potential source of pain in total knee arthroplasty patients. This study assessed the location inside the patella having largest stress change after implantation of an ultra high molecular polyethylene patella button. Finite elements models of the patellae before and after implantation of patellar button were created. Experimentally determined spring constants of muscles and ligaments, and patellofemoral contacting loads were applied to the models at 30 degrees , 60 degrees , and 90 degrees of knee flexion. The Von Mises stress of the intact patella decreased with increased knee flexion, while that of implanted patella increased. Also, the stress range in the implanted patella was 3-9 times higher than in the intact one. The highly stressed region of the intact patella moved proximally with higher knee flexion angles, while that of the implanted model stayed near the central anterior patella. At 90 degrees of knee flexion, the stress in the anterodistal patella increased considerably after implantation of a patella button so that the anterodistal patella may be susceptible to be painful source after the total knee replacement.

Analytical study of tensile behaviors of UHMWPE/nano-epoxy bundle composites

Ultra-high molecular polyethylene (UHMWPE) fiber reinforced nano-epoxy and pure epoxy composites in bundle form were prepared and tested for tensile properties. UHMWPE fiber composites are well known for their superior tensile performance, and this work was conducted to assess the effect of adding nanoadditives to the resin and to evaluate possible enhancements or degradations to that attribute. The results showed that tensile tests on various types of UHMWPE fibers/nano-epoxy bundle composites resulted in an increase in modulus of elasticity due to the addition of small amounts of reactive nanofibers (r-GNFs) to epoxy matrix. It was observed that the modulus of elasticity of the composite bundles depended on both volume fractions of the matrix and the weight percent (wt%) of r-GNFs in the matrix. A non-linear relationship was established among them and an optimal modulus was determined by calculation. A three-dimensional surface plot considering these two parameters has been generated which gives an indication of change in modulus of elasticity with respect to volume fraction of matrix and wt% of r-GNFs in the matrix. A Weibull analysis of tensile strengths for the various bundle composites was performed and their Weibull moduli were compared. The results showed that presence of r-GNFs in the composites increased the strength effectively, and 0.3 wt% r-GNFs based composites showed the highest strength. An important ancillary finding is that optimum tensile values are a function not only of the above parameters, but also strongly influenced by the addition of diluents which control the viscosity of the blend.

Development of the conductive polymer matrix composite with low concentration of the conductive filler

Composite particles with ultra-high molecular polyethylene (UHMWPE) core and carbon black (CB) or carbon nanotube (CNT) shell were produced by particle composite system, then molded into conductive polymer composites. Morphology of these composite particles was investigated by scanning electron microscopy (SEM). Matrix particles are coated with CB or CNTs very well. And CNTs are not being cut short. The results of electrical behavior study show that these polymer composites have low percolation threshold. Conductive networks of CB and CNT were seen by optical microscopy. Related mechanism is discussed.

Hysteretic Heating During Cyclic Loading of Medical Grade Ultra High Molecular Weight Polyethylene (UHMWPE)

Ultra high molecular polyethylene (UHMWPE) is used in artificial knee joints and therefore subjected to cyclic loading. The hysteretic thermo-mechanical response of medical grade ultra high molecular weight polyethylene under compressive cyclic loading at high stress levels was investigated. It was shown that the repeated loading leads to heat dissipation that heavily alters the properties of the polyethylene and is crucial to its fatigue behaviour.

Preparation of Conductive Composite Particles by Impact Coating Process

PCS (particle composite system) is a kind of dry coating equipment. The PCS process involves encapsulating UHMWPE (ultra-high molecular polyethylene) particles with a layer of SCB (super conductive carbon black) or ACB (acetylene black), and subsequently compacting these CB-encapsulated UHMWPE powders by compression molding to manufacture conductive polymer composites respectively. Morphologies of these composite particles were investigated by SEM. By SEM, we can see the conductive networks of CB in polymer composites. Coating-molding process with PCS can be used to form network structure in ceramics and metal as well.

Technology and Some Mechanical Properties of Biocomposites Based on Mineral Components

Two types of new composite implant materials are investigated. Their mechanical characteristics, biocompatibility, and the dynamics of bond strength between the biocomposites and a live bone tissue are determined. The first type of the biomaterials is based on silicate glass and hydroxyapatite. Both the natural and a synthetic hydroxyapatite were used. The second type of the biomaterials was made of an ultrahigh-molecular polyethylene and the synthetic hydroxyapatite. Composite materials of both the types were implanted in the rabbit femur. The bond strength between the bone tissue and the implants was determined in 2, 4, 10, and 25 weeks.

The Significance of Dielectric Spectroscopy in the Study of Transition Dynamics and Morphology of Transcrystallinity in Polymeric Composites

Transcrystallization, characterized by dense nucleation on the fiber surface and constrained radial crystalline growth, results in different crystalline morphology than that of the bulk. Concomitantly, it results in redistribution of the amorphous phase, generating rearrangement of the phase transition pattern. This can be identified by dynamic energy dissipation techniques such as highsensitivity dielectric spectroscopy performed in this study. Focusing on the glass transition, the dielectric properties of three sets of composites are considered, namely, aramid fiber-reinforced nylon 66, aramid fiber-reinforced poly(ether ether ketone), and ultrahigh molecular weight fiber-reinforced high-density polyethylene. This study demonstrates that dielectric spectroscopy is a unique experimental tool, highly sensitive to the presence of transcrystallinity via its effect on amorphous phase redistribution. Its sensitivity is reflected by a range of dielectric parameters, namely, the activation energy, the dielectric strength and Kirkwood correlation factor, the loss tangent, and the relaxation peak broadening. A number of composite–dielectric property combinations are presented.

超高分子量ポリエチレンのトライボロジ特性と磨耗粉の細胞毒性(OS.2 バイオエンジニアリング)

The ultra high molecular polyethylene (UHMWPE) with the molecular weight of 115x10^4, 249x10^4, and 340x10^4 were manufactured. The additive, density, and molecular weight distribution of the specimens were controlled to be identical to each other. A friction test using a reciprocating tester revealed that the coefficient of friction of the specimen excluding anti-oxidant monotonically increased with friction distance. The contact of UHMWPE wear particles with macrophages for 48 hours was performed by means of a newly developed cell culture method; flip cell culture method. Lactate dehydrogenase (LDH) activity was measured to evaluate the cell toxicity of the wear particle. Molecular weight dependence was observed in the cell toxicity; the LDH activity was highest in the specimen with molecular weight of 240x10^4. The number of wear particle smaller than 15 μm was also largest in the specimen. These results suggest that the molecular weight of UHMWPE affects the size of wear particle, and the size then affects the cell toxicity.

人工膝関節用超高分子量ポリエチレンの微小領域における変形挙動(S04-4 医療とバイオエンジニアリング,工学技術の医療応用(4),S04 医療とバイオエンジニアリング,工学技術の医療応用)

So-called "delamination destruction" is often observed on ultra-high molecular polyethylene (UHMWPE) knee components. We reported that the grain boundary becomes the place at which destruction takes place and presence of D,L-α-Tocopherol (vitamin E:VE) at the grain boundary prevents crack propagation. It was also reported that partial hardening (or degradation) might be prevented by the anti-oxidization effect of VE. The purpose of this study is to clarify the mechanism in which VE suppresses the influence of gamma-ray irradiation, and the mechanism of delamination destruction using the image correlation method with tensile-testing. The results showed that the increase-rate of volume strain in the grain boundary was lower than at in grain for the gamma-irradiated UHMWPE. In contrast, the virgin sample and the VE added sample show contrary results.

In situ prepared composite of ultrahigh molecular mass PE and PANI

Crystallinity parameters and changes in the crystalline morphology with temperature of an electrically conductive composite containing ultrahigh molecular mass polyethylene (UHMMPE) and polyaniline (PANI) doped with dodecylbenzenesulfonic acid (DBSA) are studied for the first time by using differential scanning calorimetry and wide-angle X-ray diffraction. It is found that during the melting of UHMMPE crystals PANI partially penetrates in the amorphous phase of the matrix polymer. Since the composite is found to be thermally stable up to ca. 270°C, it can be suggested that it would be processable without loosing conductivity at temperatures much higher than the melting temperature of UHMMPE.

膝関節シミュレータによる軟質材を用いた人工膝関節の流体潤滑膜形成の評価(G02-4 人工関節,G02 バイオエンジニアリング部門)

Artificial joint is generally applied for surgical operation on the patients of osteoarthritis, rheumatoid arthritis etc. Current major artificial knee joint is composed of metallic or ceramic femoral component and tibial component of Ultra high molecular polyethylene (UHMWPE), and this constitution is durable for more than 10 years in clinical use. However, it is indicated that wear debris of UHMWPE activates phagocyte or macrophage excessively, and finally the problem of loosening occurs. One of the solutions to reduce wear debris is to apply fluid film lubrication mode constructively. We observed the degree of the fluid film formation of artificial knee joint utilizing electric resistance method. In experimental processes, artificial knee joint was installed in the knee joint simulator, which could generate practical condition of walking in 4-degrees of freedom. The experimental result showed that high degree of separation by fluid lubrication occurred in the condition of tibial component of UHMWPE flat plate. Furthermore, the application of compliant material as rubbing surface improved fluid film formation in simulator test.