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Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-09-12Bitstream added on 2014-06-13T19:11:30Z : No. of bitstreams: 1 correa_lo_me_bauru.pdf: 5256316 bytes, checksum: aeb1ed9766d5fbcaa77acd3c1479f4cf (MD5) / O presente trabalho teve o objetivo realizar um estudo do desempenho do corte do material Polietileno de Ultra Alto Peso Molecular (UHMWPE), em operação de torneamento, através da medição da força principal de corte, analisando-se a influência dos seguintes parâmetros: avanço, velocidade de corte, profundidade de corte e geometria da ferramenta. A medição da força de corte foi feita por um dinamômetro conectado ao sistema de aquisição de dados, durante a usinagem realizada em um torno mecânico horizontal. A partir dos resutados obtidos, foi possível indicar as condições de corte mais adequadas em relação aos valores da força de corte medidas, para as condições de qualidade superficial aceitáveis em operações de desbaste. / The objective of this work is to carry out a study about the action cut of the Polyethylene of Ultra Hight Molecular Weight (UHMWPE) material, analyzingh the influence of there parameters: feed, cutting speed, depth of cut and the geometry of the tool. The measurement of the cutting force was made a connected dinamometric to the acquisition data system, during the machining in a horizontal mechanical lathe. By the obtained results was possible to indicate the more appropriate cutting condictions related to the values of the measured cutting force, to the condictions of superficial quality accepted in roughness operation.

Ultra-high molecular weight polyethylene (UHMWPE) is an engineering polymer that is utilized in many applications. Due to the presence of a transient physical network of entanglement, the processing of UHMWPE through conventional melt-extrusion techniques is extremely challenging. Reducing entanglement may provide a way to produce UHMWPE with superior mechanical properties by increasing the possibility of chain extension and chain orientation. A novel solvent-free route has been shown to produce disentangled UHMWPE by controlling the polymer synthesis. The polymerization conditions play a pivotal role in determining the entanglement density of UHMWPE. Homogeneous and heterogenous synthesis routes for the production of disentangled UHMWPE are viable. This Master Thesis performed sensitivity analysis on the controlled synthesis of disentangled UHMWPE based on MAO-activated bis(phenoxy imine) titanium dichloride catalytic system. Both Homogenous and heterogeneous synthesis routes were investigated and compared in terms of polymerization activity as well as entanglement density utilizing thermal, rheological, and morphological analysis techniques. Under the studied polymerization conditions, the catalytic system is able to produce disentangled UHMWPE with a minimum weight-average molecular weight of 4 million grams per mole via homogeneous as well as heterogeneous synthesis routes.

The research presented in this thesis represents an effort to characterize the properties of ultra-high molecular weight polyethylene (UHMWPE). As a composite of polymers, the properties of UHMWPE are time-dependent. It is desired by research sponsors to know the properties of the material at high strain rates, in order to simulate the use of these materials in computer models. Properties believed to be significant which are investigated in this research are the tensile properties of lamina and laminates, and the interlaminar shear properties of laminates. The efficacy of using time-temperature superposition to shift tensile properties of the composite is investigated, and a novel apparent shear strength test is proposed and demonstrated. The effects of processing the material at various temperatures and pressures are also investigated. / Master of Science

Made available in DSpace on 2015-04-01T12:17:40Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3247441 bytes, checksum: c1dfc0c3debca7991c14dcc71ed16144 (MD5) Previous issue date: 2013-11-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The current work aims at investigate the effect of incorporation of a new antioxidant vitamin C(ascorbic acid) in ultrahigh molecular weight polyethylene (UHMWPE) matrix from thermooxidation perspective. Ultrahigh molecular weight polyethylene/vitamin C) blends, with different vitamin C contents (0.5, 1 and 2 wt%) were prepared via compression molding technique, have been investigated using several analytical steps (SEM, DSC, TG, FTIR and antioxidant activity). Thermal degradation behavior of neat UHMWPE and its blends were estimated using the Friedman, the Ozawa, Flynn, and Wall (OFW) methods. Results indicated that the polymer/vitamin C blends have homogeneous morphology. The addition of ascorbic acid seems to have no influence in crystallization and melting properties of the polymer. Moreover, the antioxidant activity of Vitamin C remained in their mixtures with UHMWPE. The analysis of the fracture surface of UHMWPE / vitamin C showed that there was no adhesion between the phases and Spectroscopy results do not show chemical interaction between UHMWPE and vitamin C. In addition, vitamin C was effective to secure the thermal performance of UHMWPE, especially when added at a concentration of 1%wt, it´s increasing the activation energy (Ea) of UHMWPE without changing its profileof reaction order (n). / O presente trabalho teve por objetivo investigar o efeito da incorporação de vitamina C(ácido ascórbico) como um novo antioxidante na matriz de polietileno de ultra alta massa molar (UHMWPE). Foram investigadas misturas de UHMWPE com diferentes teores de vitamina C (0,5;1 e 2%em peso) preparadas por moldagem por compressão. Todas as amostras foram caracterizadas por diferentes técnicas analíticas (MEV, DSC, TG, FTIR e atividade antioxidante). Parâmetros da degradação térmica do UHMWPE puro e incorporado com vitamina C foram determinados pelo método de Friedman, Ozawa, Flynn, e Wall (OFW). Os resultados encontrados apontam para uma distribuição homogênea da vitamina C na matriz polimérica. A sua adição não afetou os processos de cristalização e de fusão da matriz de UHMWPE. Além disso, a atividade antioxidante da vitamina C se manteve nas suas misturas com o UHMWPE. A análise da superfície de fratura do UHMWPE/vitamina C mostrou que não ocorreu adesão entre as fases e a análise de infravermelho indicou a falta de interação química entre estes componentes. Finalmente, a vitamina C foi eficiente para garantir a performance térmica do UHMWPE, principalmente quando foi adicionada em uma concentração de 1% em peso, de modo a aumentar a energia de ativação (Ea) do UHMWPE sem alterar o seu perfil da ordem de reação (n).

A considerable number of total-joint replacement devices used in orthopedic medicine involve articulation between a metallic alloy and ultra-high molecular weight polyethylene (UHMWPE). Though this polymer has excellent wear resistance, the wear particulate 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. This study presents two alternate approaches to improving the wear performance of UHMWPE in orthopedic applications Previous work has shown that UHMWPE-based composites have wear resistance comparable to the irradiation-crosslinked polymer. Zirconium has been shown to have excellent corrosion resistance and biocompatibility, and the authors have used the material as reinforcing filler in UHMWPE with promising results. Compression-molded UHMWPE composites with up to 20 weight percent (wt%) of micro-sized 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 orthopedic applications and may provide a viable alternative to the property tradeoffs encountered with irradiation crosslinking. Apart from UHMWPE, novel materials including hydrogels and bio-derived polymers show great potential in orthopedics, but such materials require the development of innovative fixation techniques [1-3]. The development of controlled porous UHMWPE morphologies offers the opportunity to utilize and expand these developing technologies. Interconnected porous structures were prepared by dry mechanical mixing of NaCl particles and UHMWPE powders followed by compression molding. Samples were soaked in water to remove the embedded salt, leaving a porous UHMWPE structure. Computational simulations of porogen distribution and leaching predicted leaching to be 95% effective when initial salt concentrations were 60wt% and higher, which was found to match very well with the experimental data. It was found that varying the concentration and particle size of the porogen can tailor the final pore morphology to a specific application, while DMA results showed that storage and loss moduli depend greatly on porosity, but not on pore size. Finally, porous UHMWPE scaffolds were successfully impregnated with gelatin, confirming the compatibility of UHMWPE with hydrogel-based fillers.

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used as a ski sole material for many years due to its good tribological properties, good wear resistance and low friction coefficient. Recent studies have showed improved performance on wear rate and hydrophobicity with nanoparticle reinforced UHMWPE. In this study, different kinds of nano-composite UHMWPE’s were tested on snow to investigate if they are suitable as a ski sole material and to find the type of nano-composite UHMWPE that has the greatest potential. Further, the mechanisms of hydrophobicity and its influence on the friction level were examined. The friction coefficient was measured in a ski test rig and simple demonstrations under a microscope were made to simulate how water is dragged along the ski sole in contact with wet snow. Mechanical properties were measured with a CSM Nanoindentation Instrument and surface topography was examined in a Wyko Optical Profiler. The cross-linked UHMWPE material showed the lowest friction coefficient on snow. The hydrophobic demonstrations, together with the ski test results, questions the suggestion that high hydrophobicity enhances the ski glide. Nanoindentation was proved to give valuable data for mechanical properties, but it should be questioned whether it is a good technique for comparing different nano-composite UHMWPE materials. The ski tests show the importance of the characteristics of snow.

The research presented herein is an effort to support computational modeling of ultra-high molecular weight polyethylene (UHMWPE) composites. An effort is made to characterize the composites and their constituents. UHMWPE, as a polymer, is time and temperature dependent. Using time-temperature superposition (tTSP), the constituent properties are studied as a function of strain rate. Properties that are believed to be significant are fiber tensile properties as a function of strain rate, as well as the through-thickness shear behavior of composite laminates. Obtaining fiber properties proved to be a challenge. The high strength and low surface energy of the fibers makes gripping specimens difficult. Several different methods of fixturing and gripping are investigated, eventually leading to a combination of friction and adhesion approaches where a fiber was wrapped on an adhesive coated cardboard mandrel and then gripped in the test fixture. Fiber strength is estimated using tTSP to equivalent strain rates approaching 10^6 sec^-1. Punch-shear testing of UHMWPE laminates is conducted at quasi-static strain rates and the dependence of the results on thickness and test geometry is investigated. / Master of Science

Multidirectional motion occurs in total knee replacements (TKR), is a major factor in ultra high molecular weight polyethylene (UHMWPE) wear and is a requirement for wear tester and simulators. There are three ways the femoral component can move relative to the tibial component; sliding, rolling and gliding and these are defined by the slide to roll ratio. Previous wear tester research has investigated the effects of multidirectional motion and slide to roll ratio, individually but not combined. The project aim was to design a machine that combined multidirectional motion with variable slide to roll ratio. A three station wear testing machine was designed and built featuring flexion extension, variable anterior posterior translation, variable internal external rotation and a 2KN load per station. The TKR was simplified to a cylinder on flat. Lubrication was 25% bovine serum and each station had its own recirculation system. A million cycle validation test was successfully carried out on non-irradiated UHMWPE samples using a slide to roll ratio of 1 : 0.5 and the mean wear rate was 14.7mg/10^6 cycles. Polished areas and scratches from 3rd body abrasion were observed. Magnification revealed a fine ripple pattern with a 1-2 micron periodicity. Ripples were randomly oriented, perpendicular to the primary direction of motion and a small number were running parallel to the primary direction of motion, indicative of rolling motion. The results from the validation study show that the knee joint wear tester is capable of producing wear rates and wear mechanisms similar to those observed in other wear testers and knee joint simulators and has met the aim of the project.

Stricter environmental regulations and trend of decreasing cost and increasing operational efficiency are the driving forces for the improvement of the tribological performance in many different industries. For example, in the case of hydropower plants, there has been increasing research carried out to achieve oil-free stations, which would substitute the oil-based lubricants with environmentally accepted lubricants or water. In this application, water could be a good alternative due to its availability and low cost. Also, water is non-toxic and has high heat capacity. Although advantageous, using water as a lubricant presents many challenges that limit its application such as corrosiveness and thin lubricant film due to its physical properties. Therefore, the material selection for the interacting surfaces needs to be correctly performed when considering water-lubricated conditions because of the harsher tribological conditions to which they will be susceptible. Polymeric materials, such as Ultra High Molecular Weight Polyethylene (UHMWPE), are good candidates for such water-lubricated applications due to versatile mechanical and thermal properties, as well as good tribological characteristics. Today, these materials find use in different tribological components, such as, bearings, liners, and gears. However, high wear rates limit their applications, due to the reduced operating life. The performance can be improved in different ways, including surface modification, polymer blending, and use of reinforcements. A novel research area is hybrid and multiscale reinforced composites, which combines the use of micro and nanofillers to obtain improved performances. UHMWPE has been thoroughly studied, including mechanical, thermal and tribological behavior. However, there are limited studies on the effects of hygrothermal aging on the friction and wear response of UHMWPE. The studies are even more restricted when considering reinforced materials. Therefore, this work aims to investigate the effect of hygrothermal aging in the tribological performance of UHMWPE composites in water-lubricated conditions. Aging exposure and tribological tests were performed to evaluate the response of the materials, and the main conclusion of this work is that the tribological response of UHMWPE composites was not significantly affected by the test exposure conditions.