Le polyéthylène à ultra haute masse molaire (UHMWPE) présente une viscosité si forte à l’état fondu que seuls des procédés de mise en forme de type frittage peuvent être employé. Ce procédé rarement utilisé pour les polymères reste peu étudié. En particulier les deux principaux mécanismes généralement mentionnés que sont le réenchevêtrement et la cocristallisation aux interfaces sont difficilement observables séparément. Le UHMWPE, grâce à sa très haute viscosité à l’état fondu et grâce à son plateau caoutchoutique extrêmement étendue en température, peut faire l’objet d’essais mécaniques à la fois à l’état semi-cristallin et à l’état fondu. Des poudres natives de UHMWPE de masses molaires comprises entre 0,6 et 10,5 Mg.mol-1 sont utilisées comme matériau de départ pour leur mise en oeuvre par frittage. La consolidation des interfaces par soudage des particules a été effectuée sous pression à différentes températures supérieures au point de fusion et pour différentes durées. Des expériences de traction effectuées soit à température ambiante soit au-dessus du point de fusion ont permis de distinguer le rôle de l'interdiffusion des chaînes au travers des interfaces de celle de la cocristallisation dans les mécanismes de soudage de particules. Il s'est avéré qu’un soudage efficace se produit dans une échelle de temps très courte. La très faible influence de la durée de frittage par rapport à celle de la température de frittage a prouvé que l'interdiffusion des chaînes n'est pas régie par un mécanisme de reptation. L'explosion à la fusion des cristaux « hors-équilibre » de la poudre native est suggérée être le mécanisme principal permettant un réenchevêtrement dans un laps de temps beaucoup plus court que celui de la reptation. La cocristallisation est un phénomène si efficace dans la consolidation de l'interface à l'état solide qu'elle masque significativement la cinétique de réenchevêtrement gouverné par la température, visible dans les tests mécaniques à l’état fondu. / One of the main issues of ultra-high-molecular-weight polyethylene (UHMWPE) is to overcome its very high viscosity. Powder sintering is then often required instead of injection or extrusion. However, sintering mechanisms remain partially understood. Indeed, the two main mechanisms generally mentioned for interparticle welding, i.e. re-entanglement and cocrystallization, can hardly be observed separately. Fortunately, due to its very high molecular weight, UHMWPE exhibits an exceptionally broad rubbery plateau so that mechanical tensile tests can be easily performed both below and above the melting point. Four UHMWPE of molecular weight in the range of 0.6.106 g.mol-1 to 10.5.106 g.mol-1 have been processed by means of sintering of nascent powders. The interface consolidation or particle welding was carried out under pressure at various temperatures above the melting point and for various durations. Tensile drawing experiments performed either at room temperature or above the melting point enabled to discriminate the role of chain interdiffusion through the particle interface from that of cocrystallization in the mechanism of particle welding. It turned out that an efficient welding occurred within a very short time scale. The very weak influence of sintering time compared to that of sintering temperature gave evidence that chain interdiffusion was not governed by a reptation mechanism. The entropy-driven melting explosion of the “non-equilibrium” crystals in the nascent powder is suggested to be the main mechanism of the fast chain reentanglement and subsequent particle welding within a time scale much shorter than the reptation time. Cocrystallization is so much efficient in the interface consolidation in the solid state that it significantly hides the temperature-governed kinetics.

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This work examines the chemical and physical effects of a material treatment process on the biopolymers PEEK, POM-h, POM-c, PTFE and UHMWPE. The polymers are analyzed physically and chemically using atomic force microscopy, profilometry, scanning electron microscopy, optical microscopy, contact angle measurement, FT infra-red spectroscopy and energy dispersive X-ray spectrometry. PEEK is found to be the most suitable polymer and FT Infra-red spectroscopy an informative analytic tool.

CHARLES UNIVERSITY IN PRAGUE FACULTY OF SCIENCE DEPARTMENT OF BIOCHEMISTRY PRAGUE 2010 Supervisor: Doc. MUDr. Jiří Gallo, PhD. Supervisor-consultant: Prof. RNDr. Gustav Entlicher, CSc. Eva Zolotarevová Summary of PhD Thesis POLYETHYLENE WEAR PARTICLES AROUND TOTAL JOINT REPLACEMENTS - THEIR PROPERTIES, DISTRIBUTION AND POSSIBLE MECHANISM OF THEIR ADVERSE BIOLOGICAL EFFECTS PRAGUE 2010 The research project was supported by the Grant project of National research program II. (no. 2B06096) of the Czech Ministry of Education, Youth and Sports named "Observation and minimization of UHMWPE wear in joint replacements". Front-page picture: Polyethylene wear particle isolated from granuloma tissue surrounding total hip replacement; Electron microscope microphotograph; particle size app. 90 x 80 µm; retouched Eva Zolotarevová Introduction Introduction For many people all over the world a replacement with an implant of irreversibly damaged joint is often the only way how to come back to normal life without pain and mobility limitation. Nowadays, greater and greater requirements are asked of quality of all replacement components, especially in terms of quality of used materials. Biomechanical properties of hip and knee replacements have been already solved. The most often used materials for manufacturing joint...

Made available in DSpace on 2017-07-21T20:42:32Z (GMT). No. of bitstreams: 1 Melina Correa Gabriel.pdf: 5915390 bytes, checksum: bae67fca28fd7999823fa6ec6ac98844 (MD5) Previous issue date: 2010-03-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The intention of this exploratory research is to study the modifications provided by high-energy mechanical milling in ultra-high molecular weight polyethylene (UHMWPE) and mixtures of this polymer with polyethylene glycol (PEG). These modifications can be of interest for future processing of UHMWPE. The mechanical milling was performed in an attritor mill, a type of mill that can be used in laboratory as well as in industry. The millings of UHMWPE were performed in different rotation speeds. For mixtures of UHMWPE and PEG, the amounts of PEG were also different. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The mechanical milling modified the UHMWPE particles morphology: with milling, the almost rounded shape became flat-like shape. This caused the reduction of apparent density of polymer after milling. The mechanical milling also provided structural changes. With the increasing of the rotation speed,there was the increasing of the monoclinic phase and the decreasing of the orthorhombic, up to 500 rpm. For 600 rpm, the amount of monoclinic phase decreased. In this rotation, the deformation rate probably increased the process temperature, allowing the monoclinic phase to return to its initial structural orthorhombic form. In mixtures of UHMWPE and PEG, after mechanical milling, the particles of PEG were probably reduced and better dispersed in the UHMWPE matrix. Changes in thermal characteristics of polymers also could be noted. The kinetics of UHMWPE crystal growth changed, as well as the behavior of PEG crystallization. Feasibly, dispersed particles of PEG acted as physical barriers against the crystalline phase growth of UHMWPE and the crystallization temperature of PEG decreased, when the UHMWPE and PEG mixtures were milled. / Este trabalho exploratório teve por objetivo estudar as modificações promovidas por moagem de alta energia no de polietileno de ultra-alta massa molar (PEUAMM) e sua mistura com polietileno glicol (PEG), que podem ser de interesse para auxiliar um posterior processamento do PEUAMM. As moagens foram realizadas em um moinho do tipo attritor, um tipo de moinho que pode ser usado tanto em laboratório quanto em escala industrial. Foram variadas as velocidades de rotação na moagem do PEUAMM, além das concentrações de PEG, quando feita a mistura. As amostras foram caracterizadas por microscopia eletrônica de varredura (MEV), microscopia de força atômica (MFA), calorimetria exploratória diferencial (DSC) e difração de raios X. A moagem de alta energia do material modificou a forma das partículas de PEUAMM, passando de arredondadas a flakes, com a evolução do processo de moagem, fazendo com que a densidade aparente do polímero diminuísse muito comparado ao polímero não moído. A moagem também proporcionou mudança estrutural, permitindo a formação de fase monoclínica em detrimento da ortorrômbica. A medida que se aumentou a rotação do moinho até 500 rpm, houve um crescimento da fase monoclínica. Apenas para 600 rpm, a quantidade dessa fase sofreu decréscimo, devido possivelmente ao aumento da frequência de choques e da temperatura de processamento, fazendo com que a estrutura monoclínica retornasse à estrutura ortorrômbica original. Na mistura de PEUAMM com PEG, a moagem provavelmente permitiu redução das partículas e a melhor dispersão de PEG na matriz de PEUAMM. Também se observaram mudanças nas características térmicas dos polímeros na mistura após moagem. Ocorreu mudança na cinética de crescimento dos cristais de PEUAMM e mudança no comportamento de cristalização do PEG, comportamento este que não ocorreu para o PEUAMM moído ou para a mistura de PEUAMM com PEG antes da moagem. Possivelmente, as partículas dispersas de PEG atuaram como barreiras ao crescimento da fase cristalina do PEUAMM e houve diminuição da temperatura de cristalização do PEG, na mistura com PEUAMM após moagem.

Made available in DSpace on 2017-07-21T20:42:32Z (GMT). No. of bitstreams: 1 Luciana Biagini Mendes.pdf: 7206159 bytes, checksum: d493f2f21ec603c56bf971cd0445a8f6 (MD5) Previous issue date: 2010-08-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research was an exploratory study of the changes that high energy mechanical milling can induce in ultra high molecular weight polyethylene (UHMWPE), using the mills Spex, Attritor and Planetary, and several times and reasons for grinding. The milling products were characterized using scanning electron microscopy (SEM), optical microscopy (OM), differential scanning calorimeter (DSC), x-ray diffraction (XRD), x-ray fluorescence (XRF), and intrinsic viscosity for calculate the viscosity average molecular weight. For the analysis of micrographs observed the morphological change of particles with the grinding, the particles are initially rounded and the milling time increases the aspect ratio, acquire the form of flakes. Changing the shape in Spex mill occurs in less time, because it is a mill more energetic that Attritor and Planetary. By analysis of DSC was possible to observe the influence of high energy mechanical milling on melting and crystallization temperatures, and the percentage of crystalline phase of UHMWPE. Was used deconvolution of peaks in xray diffraction patterns for better identification of the peaks of monoclinic and orthorhombic crystalline structures. Observed the formation of monoclinic phase in the UHMWPE processed in high energy mills, to a greater percentage in the mill Attritor, possibly because it has a temperature control and avoiding a reversal of the monoclinic crystalline structure in orthorhombic crystalline structure. / Este trabalho foi realizado para um estudo exploratório das modificações que a moagem de alta energia pode provocar no polietileno de ultra alta massa molar (PEUAMM), utilizando os moinhos Spex, Attritor e Planetário, e variando tempo e poder de moagem. Os produtos de moagem foram caracterizados utilizando microscopia eletrônica de varredura (MEV), microscopia ótica (MO), calorimetria exploratória diferencial (DSC), difração de raios x (DRX), fluorescência de raios x (FRX), e medidas de viscosidade intrínseca para o cálculo da massa molar viscosimétrica média. Pelas análises das micrografias observou-se a mudança morfológica das partículas com a moagem, inicialmente as partículas são arredondadas e com o tempo de moagem aumentam a razão de aspecto, adquirem a forma de flakes. Para o moinho Spex a mudança da forma das partículas ocorre em menor tempo, por este ser um moinho mais energético que o Attritor e Planetário. Pela análise do DSC foi possível observar a influência da moagem de alta energia nas temperaturas de fusão e cristalização, e na porcentagem de fase cristalina do PEUAMM. Foi utilizada a deconvolução de picos nos difratogramas de raios x para melhor identificação dos picos das estruturas cristalinas ortorrômbica e monoclínica. Com a moagem de alta energia ocorreu a formação da estrutura cristalina metaestável monoclínica, em maior porcentagem no moinho Attritor, possivelmente por este possuir um controle de temperatura e evitando uma reversão da estrutura cristalina monoclínica em ortorrômbica.

La Compaction à Grande Vitesse (CGV) est un procédé efficace pour mettre en oeuvre par frittage, et dans un temps court, des poudres polymères semi-cristallins quelle que soit leur viscosité en partant d’une température inférieure au point de fusion. L’échauffement et la fusion du matériau est obtenu par une succession d’impacts à une énergie donnée ce qui offre la possibilité de définir finement la quantité d’énergie que l’on souhaite apporter au matériau et la qualité du frittage. Une fusion partielle de la poudre permet de profiter de la cristallinité élevée de la poudre native, un compromis est alors possible entre de hautes propriétés élastiques et une ductilité élevée. La contre-partie de cette efficacité est une mise au point délicate du procédé. Dans le cas du polyéthylène ultra haute masse molaire (UHMWPE), il a été montré que le procédé permet une quasi-abstraction des effets de la masse molaire. Le frittage du UHMWPE demande seulement une réorganisation à courte distance des chaînes qui peut se faire dans un temps très limité. La cohésion de la poudre est assurée essentiellement par la cocristallisation et la création de nouveaux enchevêtrements. La modélisation du procédé a permis de comprendre comment l’énergie cinétique lors des impacts est transformée en chaleur dans la poudre et elle a permis l’établissement d’un critère de processabilité par CGV. Ce critère de processabilité repose sur la déformabilité de la poudre contenu dans la matrice au moment de l’impact. Celle-ci doit être suffisante pour que l’énergie dissipée dans le matériau permette sa fusion en moins de cent coups. Ceci a permis de comprendre pourquoi le polyoxyméthylène peut difficilement se mettre en forme par CGV. / High Velocity Compaction (HVC) is an efficient process to mold, in a short time, semicrystalline polymers powders any about their viscosity by starting from a temperature below melting point. Heating and melting occur by successive impacts at a preset energy that offers the possibility to set accurately the energy amount that we would bring to the material and the sintering quality. Partial melting of powder enable to take advantage of the high cristallinity of nascent powders, a compromise is possible between high elastic properties and high ductility. The flip-side of this efficiency is a delicate process settings. For the ultra high molecular weight polyethylene (UHMWPE), it has been shown that the process makes it possible a quasi abstraction of molecular weight effects. UHMWPE sintering needs only a short length reorganisation of chains that could be done in a really short time. Powder cohesion is essentially bring by cocrystallisation and by new entanglements creation. Process modelling allowed to understand how kinetic energy during hits is converted into heat in powder and it’s enable to define a HVC processability criterion. This processability criterion rests on the strainability of powder place in a die during a hit. It has to be sufficient to the dissipated energy in material allows his melting in less than one hundred impacts. This criterion allows to understand why the polyoxymethylene is hard to mold by HVC.

The transition to a Circular Economy scheme that enables a more efficient usage of the resources is one of the most pressing needs in our society. From the industrial perspective this has been translated into new design philosophies and the search for more efficient systems. Polymeric composites have played a key role in the development of lighter components with good mechanical and tribological properties. Specifically, the demand of Carbon Fiber Reinforced Polymers (CFRP) has had an increasing trend since 1970s-1980s, becoming one of the kind of composites with the highest demand in the market to supply industries such as aerospace, automotive, construction, renewable energies, among others. With the increasing demand of CFRP materials some of the main challenges that arise are their disposal, environmental impact and cost of production to maintain the required supply. The use of Carbon Fibers as a reinforcement for polymeric matrices has been widely documented over the last decades, however the characterization of recycled Carbon Fibers for tribological applications is still scarce. Therefore, this investigation is focused on the mechanical and tribological characterization under water lubricated conditions of Ultra High Molecular Weight Polyethylene (UHMWPE) composites reinforced with virgin and recycled Carbon Fibers and Graphene Oxide. The findings of this work provide an important panorama regarding the performance of recycled Carbon Fibers, showing that they can have a comparable performance in mechanical properties and tribological behavior. This enables the use of recycled Carbon Fibers without compromising performance while reducing the environmental impact and cost.