Lors de ce travail nous avons étudié les modifications de HDPE, PVF, PVDF et PTFE par des plasmas O2 et N2. Nous nous sommes focalisés sur l’effet des ions et des neutres. Nous constatons dans tous les cas une modification de la composition des échantillons, cette modification de composition est accompagnée d’une modification de l’énergie de surface. Les traitements plasma greffent de nouvelles fonctions polaires (oxygénées ou azotées) à la surface des échantillons, responsables de l’augmentation de l’énergie de surface. Le PTFE traité par plasma O2 présente lui un comportement particulier. Il est possible de greffer de faibles quantités d’oxygène à sa surface et d’augmenter faiblement son énergie de surface lors de traitements de courte durée à faibles puissances. Les traitements de plus fortes puissances érodent fortement la surface du PTFE sans y greffer de fonctions oxygénées. Les surfaces obtenues sont extrêmement rugueuses et leur énergie de surface est fortement diminuée, nous obtenons des surfaces de type ultra-hydrophobes. Les résultats obtenus lors des traitements plasma ont été comparés à ceux obtenus dans le cas de traitements par des ions O2+/O+ ou N2+/N+. Ceci nous a permis de mettre en évidence une différence de réactivité des échantillons face aux différents traitements. Cette différence de réactivité nous permet de conclure que les ions ne sont pas l’espèce principale responsable de la modification de nos échantillons lors des traitements plasma. Nous avons également pu mettre en évidence une différence de réactivité entre les différents échantillons. Le HDPE, PVF et PVDF ont des réactivités semblables alors que le PTFE est beaucoup plus résistant aux modifications, nous pensons que ceci est dû à la structure entièrement fluorée du PTFE. Nous avons également étudié la résistance de nos échantillons à l’adsorption de protéines dans le cadre d’une étude sur la biocompatibilité. Nous avons pu montrer que les échantillons de PTFE rendu ultra hydrophobe, après traitement par plasma O2 de haute puissance, présentent une bonne résistance à l’adsorption de protéines. Cette caractéristique est intéressante pour la synthèse de matériaux biocompatibles.

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-04-03T17:52:08Z No. of bitstreams: 1 DissVFS.pdf: 9186678 bytes, checksum: 8be68ef032b461bf1f1888d30b5928b6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-04-18T13:29:50Z (GMT) No. of bitstreams: 1 DissVFS.pdf: 9186678 bytes, checksum: 8be68ef032b461bf1f1888d30b5928b6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-04-18T13:30:00Z (GMT) No. of bitstreams: 1 DissVFS.pdf: 9186678 bytes, checksum: 8be68ef032b461bf1f1888d30b5928b6 (MD5) / Made available in DSpace on 2017-04-18T14:08:59Z (GMT). No. of bitstreams: 1 DissVFS.pdf: 9186678 bytes, checksum: 8be68ef032b461bf1f1888d30b5928b6 (MD5) Previous issue date: 2016-03-07 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Polytetrafluoroethylene (PTFE) has excellent properties such as chemical inertness and useful mechanical properties at high and low temperatures. After melt, the PTFE viscosity is so high that the extrusion and injection processing are impracticable. Alternatively, the PTFE powder is cold pressed and sintered. During the sintering, heterogeneous temperature distributions may occur because of the low thermal conductivity of PTFE and induce thermal stresses. Cracks will be initiated if such stresses exceed the failure one. Considering the raw material cost (10 US$ kg−1)) and its density (2,2 g cm−3) cracks in the sintered PTFE may cause financial losses for the manufacturing industry, which justifies the studies about this process. The main mechanisms that cause permanent strains are the crystallinity change and the closure of voids from the pressing, which makes the satisfactory modeling of the PTFE sintering be complex. This work aims to characterize the strains assigned to the crystallinity changes and develop a computational model with such mechanism concerning the sintering of PTFE parts shaped by cold pressing. An experimental apparatus for the application of optical dilatometry assisted by Digital Image Correlation (DIC) was developed and used to estimate the specific volume of the amorphous and crystalline phases during sintering. The model was implemented using the UEXPAN AbaqusTM sub routine and model’s variables were obtained from literature and / or experimentally characterized. The model was validated by an experiment with thermal gradient induced strains in a PTFE specimen and the simulation results showed good correspondence with the DIC ones. For future works, it is suggested the improvement of the model implementing the void closure mechanism and the melting and crystallization kinetics, hence, the characterization of material properties in the temperature range of the process. / O politetrafluoretileno (PTFE) possui excelentes propriedades como alta resistência química, alta capacidade de isolamento térmico e elevada gama de temperaturas de serviço. A elevada viscosidade do PTFE no estado fundido inviabiliza seu processamento por extrusão e injeção, portanto, recorre-se às rotas de fabricação não tradicionais para polímeros como a prensagem a frio seguida da sinterização do pó (ou dos pellets) do PTFE. Como o PTFE é um mau condutor de calor, podem surgir trincas na peça devido aos gradientes de deformação ocasionados pela distribuição heterogênea de temperatura durante a sinterização. Isso causaria grandes prejuízos à indústria transformadora ao se considerar o custo da matéria prima (10 US$ kg−1) e sua densidade (2,2 g cm−3), o que justifica estudos acerca do processo de sinterização. Os principais mecanismos que causam deformações permanentes são a variação do grau de cristalinidade, a qual depende das cinéticas de fusão, cristalização e degradação do PTFE, e o fechamento de vazios provenientes da prensagem. Estes mecanismos fazem com que a modelagem satisfatória da sinterização do PTFE não seja simples. O objetivo deste trabalho é caracterizar experimentalmente as deformações atribuídas à variação do grau de cristalinidade e desenvolver um modelo computacional contendo este mecanismo para a sinterização de peças de PTFE moldadas por prensagem isostática a frio. Foi desenvolvido um aparato para ensaios de dilatometria óptica assistida pela técnica de Correlação de Imagens Digitais, que foi utilizado para a caracterização dos volumes específicos das fases amorfa e cristalina do PTFE em função da temperatura e do grau de cristalinidade durante a sinterização. O modelo numérico foi implementado utilizando a sub-rotina UEXPAN do software AbaqusTM e suas variáveis foram obtidas da literatura e/ou caracterizadas experimentalmente. As potencialidades do modelo foram avaliadas em ensaio com gradiente térmico induzido e os valores provenientes da simulação mostraram boa correspondência com os experimentais, indicando que a implementação foi satisfatória dentro das simplificações utilizadas. Como perspectivas, destacam-se a sofisticação do modelo pela implementação do mecanismo de fechamento de vazios e das cinéticas de fusão e cristalização, bem como obtenção de propriedades do material que não foram encontradas na literatura para o intervalo de temperaturas do processo. / CNPQ: 130970/2014-0

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-05-30T23:20:44Z No. of bitstreams: 1 JulianaRicardoDeSouza_TESE.pdf: 14513350 bytes, checksum: 9e7d4d9cfe9132db18a4d5ee9940a771 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-06-01T23:23:24Z (GMT) No. of bitstreams: 1 JulianaRicardoDeSouza_TESE.pdf: 14513350 bytes, checksum: 9e7d4d9cfe9132db18a4d5ee9940a771 (MD5) / Made available in DSpace on 2016-06-01T23:23:24Z (GMT). No. of bitstreams: 1 JulianaRicardoDeSouza_TESE.pdf: 14513350 bytes, checksum: 9e7d4d9cfe9132db18a4d5ee9940a771 (MD5) Previous issue date: 2015-06-05 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A estocagem de rejeitos de scheelita a ?c?u aberto? resultante da explora??o da mina Breju? da regi?o de Currais Novos, Rio Grande do Norte, Brasil, tem gerado, no per?odo 1960-2015, um forte passivo ambiental. O pol?mero politetrafluoretileno (PTFE) majora em sistemas de deslizamento e reduz significativamente custos de manuten??o, devido ?s suas excelentes propriedades mec?nicas, tais como baixo coeficiente de atrito (0,01< m <0,10) e limite de escoamento da ordem de 10 MPa. No entanto, apresenta elevadas taxas de desgaste (10-13 m2/N) e por despertar o interesse cient?fico e tecnol?gico nas ind?strias petroqu?mica e aeroespacial na forma de lubrificantes s?lidos, objetivou-se desenvolver comp?sitos polim?ricos com matriz de PTFE utilizando-se o rejeito de scheelita como carga, viabilizando tamb?m processos de remedia??o ambiental. O Rejeito de Scheelita foi caracterizado na condi??o como adquirido, atrav?s de an?lises de DRX, FRX, MEV, EDS, granulometria por Peneiramento e a Laser, registrando-se tra?os de tungst?nio e metais estrat?gicos igualmente importantes. O PTFE foi analisado por TGA, DSC, MEV, DRX, FRX. Para o desenvolvimento dos comp?sitos misturou-se mecanicamente os p?s de PTFE e Rejeito de Scheelita, devidamente preparados e pesados. Para moldagem por compress?o ? quente projetou-se um molde cil?ndrico de a?o acoplado a uma resist?ncia inseridos numa prensa hidr?ulica. Avaliaram-se o desempenho tribol?gico dos comp?sitos obtidos a partir de Rugosidade, Dureza, Molhabilidade, Absor??o ao impacto, Esclerometria, Pino Disco e Analise Morfol?gica. Os resultados indicam que a varia??o no teor de rejeito de scheelita influ?ncia nos resultados de rugosidade, dureza e absor??o ao impacto. Comp?sitos molhados com ?gua salina e destilada caracterizaram-se como hidrof?bicos, enquanto que os molhados com ?leo paraf?nico e naft?nico como oleof?licos. Correlacionando os resultados dos ensaios tribol?gicos e custos constatou-se que a composi??o de 20% de Rejeito de Scheelita apresentou a melhor planicidade, baixo consumo de energia de deforma??o espec?ficica (<0,30 J/mm3), a menor perda m?ssica (8x10-3g) e afundamento da pista (<0,4 ?m/km). / The storage scheelite tailings in the open air as a result of Breju? mine exploration, located near Currais Novos, Rio Grande do Norte, Brazil, between 1960 and 2015, a strong environmental passive. The polymer polytetrafluoroethylene (PTFE) outstands in sliding systems and significantly reduces maintenance costs, due to its excellent mechanical properties, such as low friction coefficient (0,01< ? <0,10) and yield limit to the order of 10MPa. However, it has high wear rates (10-13 m2/N) and for arousing scientific and technological interests at petrochemical and aerospace industry, in the form of solid lubricants, the target was to develop polymeric composites with a PTFE matrix using tailings of scheelite as charge, enabling also environmental remediation processes. The tailing of Sheelite was characterized in acquired conditions, through XRD, XRF, SEM, EDS, granulometry by screening and by laser, recording traces of tungsten and strategic metals equally important. The PTFE was analyzed by TG, DSC, SEM, XRD, XRF. To the composites development, powders of PTFE and tailings of sheelite were mechanically mixed, previously prepared and weighed. To hot compression molding, a designed cylindrical steel mould was coupled with a resistor and placed in a hydraulic press. The composite?s tribological performance was evaluated from roughness, hardness, wettability, impact absorption, sclerometry, pin on disc, and morphological analysis. The results show that the variation in the tailing of scheelite concentration influences the results of roughness, hardness and impact absorption. Wet composites with saline and distilled water were characterized as hydrophobic, and the ones wet with paraffenic and naphtenic oil, they acted oleophilic. Correlating the results of tribological tests and costs, it was found that the composition of 20% mineral filler showed better planeness, low specific deformation energy consumption (<0,30J/mm?), the lowest mass loss (8x10-4g) and trail shipwreck (<0,4?m/km).

In this work we study the deposition of hydrophobic fluorocarbon coatings by magnetron sputtering of polymeric PTFE target. We show what is the influence of the conditions of the deposition process - the pressure in the chamber, the RF power - on the properties of the resulting CFx thin films (their chemical composition, morphology, wettability, barrier and optical properties, stability and possible bio-aplications). In this work we use a novel way to control the morphology and the chemical composition of the surface of thin films independently by using nano-particles, both metal (Pt, Cu, Al) and polymeric (C:H, Nylon). With nano-particles we can control the hydrophobicity of thin films and we can prepare super-hydrophobic films. Work has an experimental character.

no / Research and technology innovations in the 1970s led to the significant commercial practice of gas separation by membranes that exists today. These advances involved developing membrane structures that could produce high fluxes and modules for packing a large amount of membrane area per unit volume (Murphy et al., 2009). At present, the share of using a polymeric membrane in the capture of CO2 is increasing and gradually the membrane technology is considered as the promising method in separation units, although the number of commercial membranes is not high. CO2 capture from natural gas is one of the controversial topics that many researchers and engineers try to find the best method satisfying both high efficiency and low capital cost. In common, chemical physical absorption towers are applied to remove CO2 from natural gas in order to prevent pipeline corrosion, even though the other component such as H2S gives rise to operating problems. The obscure angle of a conventional unit is related to the high energy consumption while the absorbent needs to be purified by the regeneration units which implement the temperature as a unique manipulating parameter for separating amine groups. The great advantages of using the membrane in gas industry are the low capital cost, easy installation and maintenance so that for this simple reason, new membranes come to the market for different types of processes. Capture of CO2 from natural gas accounts for one of the major difficulties so that the engineers try to employ membrane modules as to alter the process efficiency. However, there are only a limited number of membranes that can be used in real industry and the research still continues over this interesting topic (Burggraaf and Cot, 1996).

Lubrificantes são produtos gasosos, líquidos, semi sólidos ou sólidos (pó) que formam um filme entre duas partes evitando o atrito. Lubrificantes de alto desempenho são designados para trabalharem em condições severas de temperatura, pressão e contaminação. Os mais utilizados são os líquidos (óleos) e semi sólidos (graxas). As graxas são aplicadas aonde o óleo pode escorrer e em pontos de difícil acesso e são divididas basicamente em duas classes, sabão e não sabão. A graxa não sabão mais utilizada é a poliuréia, obtida pela reação entre aminas e isocianato, possui elevada tixotropia, alta rigidez dielétrica e excelente poder anticorrosivo, por isso é amplamente utilizada para lubrificação de motores elétricos e maquinário naval. Para obter uma graxa com altíssimo desempenho, nesse estudo foi utilizado o fluido lubrificante sintético polialfaolefina e também foi empregado o aditivo lubrificante sólido politetrafluoroetileno (PTFE) por apresentar o menor coeficiente de atrito conhecido, é comercialmente encontrado irradiado em ar para obter partículas menores e produzir grupos terminais oxigenados que são mais compatíveis com a superfície metálica. Os ensaios foram realizados de forma comparativa usando a graxa de poliuréia pura e aditivada com PTFE. As caracterizações foram feitas por espectroscopia de infravermelho, análise elementar de C, N, e H e índice de NCO livre, comprovando a formação de poliuréia de quatro carbonos (tetrauréia). As propriedades funcionais de ponto de gota e separação de óleo mostraram alta compatibilidade e estabilidade entre os polímeros, que aumentaram quando foi adicionado PTFE. A excelente resistência da graxa de tetrauréia pura ao desgaste e extrema pressão foram demonstradas pelo teste de quatro esferas e teste prático em rolamentos, caracterizando esta graxa como de alto desempenho quando comparada com as graxas mais utilizadas no mercado. / Lubricants are gaseous, liquid, semi solid or solid (powder) materials those form a film between two parties preventing friction. High performance lubricants are designed to work under severe conditions of temperature, pressure, and contamination. The most used are liquids (oils) and semi solids (greases). Greases are applied where oils can drain or in inaccessible places and are divided generally into two classes, soap and no soap. The most used non soap grease is polyurea, obtained by the reaction between amine and isocyanate, has highly thixotropic, high dielectric strength and excellent anticorrosive property, so it is widely used for lubrication of electric motors and shipbuilding machinery. For a grease with high performance, in this study was used a synthetic lubricant fluid, polyalphaolefin, and was also employed solid lubricant additive polytetrafluoroethylene (PTFE) due its lowest coefficient of friction, is found commercially irradiated in air to obtain smaller particles and to produce oxygenated terminal groups those are more compatible with the metal surface. The tests conducted were comparatively between pure polyurea grease and with PTFE additive. The characterizations were made by infrared spectroscopy and elemental analysis of C, N and H and Free NCO index, proving the formation of four carbons polyurea (tetraurea). The functional analysis of drop point and oil separation showed high stability and compatibility between the polymers increased when PTFE was added. The excellent resistance of pure tetraurea grease to wear and extreme pressure were demonstrated by four-ball and practical bearings tests, characterizing this grease as a high performance lubricant, when compared to most used greases in the market.

Die inhärenten elastomeren Eigenschaften von Gummiwerkstoffen sind im Vergleich zu Thermoplasten in vielen Spezialanwendungen vorteilhaft. Jedoch sind ihre schlechten Reibungs- und Verschleißeigenschaften ein wesentlicher Nachteil besonders bei tribologischen Anwendungen. In der vorliegenden Arbeit wurden Reibung, Verschleiß und mechanische Eigenschaften von Gummiwerkstoffen, die Polytetrafluorethylen(PFTE)-Pulver enthalten, untersucht. Hauptziel war dabei die Verbesserung der Reibungs- und Verschleißeigenschaften bei weiterer Erhöhung der mechanischen Eigenschaften der Elastomere. Es ist bekannt, dass sich Reibungs- und Verschleißeigenschaften gummiähnlicher Materialien in vielfältiger Weise von den Reibungseigenschaften der meisten anderen Festkörper unterscheiden. Die Gründe dafür sind das viskoelastische Verhalten und der sehr geringe elastische Modul von Gummi. Die Verwendung von mit Elektronen modifizierten PTFE-Pulvern in Ethylen-Propylen-Dien-Monomer (EPDM) Kautschuken führt zu einer signifikanten Reduzierung der Reibung, Erhöhung der Verschleißfestigkeit und gleichzeitig zu verbesserten mechanischen Eigenschaften in Folge einer speziellen chemischen Kopplung zwischen dem modifiziertem PTFE-Pulver und dem EPDM. Gummirezeptur, Vernetzungsmethode und die viskoelastischen Materialeigenschaften beeinflussen wesentlich die tribologischen und mechanischen Eigenschaften. Morphologie, Dispersion und die chemische Kopplung des PTFE-Pulvers haben einen signifikanten Einfluss auf die Reibungs- und Verschleißverhalten. Die viskoelastischen Materialeigenschaften, d.h. Härte, E-Modul und tan delta (Verlustfaktor) der Gummimischungen sind kritische Parameter und erfordern deshalb eine Optimierung. In dieser Arbeit wurden zwei Modellsysteme untersucht, die auf zwei unterschiedlichen Kautschuktypen basieren: a) Ethylen-Propylene-Diene-Monomer (EPDM) Kautschuk und b) Polychloropren Kautschuk (CR). / The inherent elastomeric properties of rubber compounds in comparison to thermoplastics are advantageous in many special purpose applications. However, their characteristic poor friction and wear properties are of prime concern especially in tribological applications. In the present work, friction, wear and mechanical properties of rubber compounds based on PTFE powder have been investigated. The main aim was to improve the friction and wear properties while further enhancing the mechanical properties of rubber compounds. As known, friction and wear behaviour of rubber-like materials differ in many ways from the frictional properties of most other solids. The reason for this is the high viscoelasticity and very low elastic modulus of rubber. The use of electron-modified PTFE powder in EPDM results in significant improvement in reducing friction, enhancing wear resistance and simultaneously improving mechanical properties due to specific chemical coupling between modified PTFE powder and EPDM. The rubber formulation, crosslinking mode and bulk viscoelastic properties strongly influences friction, wear and mechanical properties. The morphology, dispersion, and specific chemical coupling of PTFE powder play a significant role on friction and wear behaviour. The bulk viscoelastic properties, i.e. hardness, modulus and tan delta (loss factor) of the compounds are critical parameters and therefore, requires optimization. In this work two model systems based on two different rubber matrixes i.e. Ethylene-Propylene-Diene-Monomer (EPDM) and Chloroprene (CR) rubber have been investigated.

Silver is a precious metal that has traditionally been used for jewellery and money. It also possesses desirable properties such as being corrosion resistant and having good electrical conductivity, resulting in its use for industrial applications. Furthermore, it is also recognised for its tribological properties in non-cost prohibitive applications. Silver can be used as a surface coating and can be deposited using an electroplating process. The utilisation of silver as a surface coating is advantageous and sustainable, as the substrate material properties are enhanced while usage of silver is kept to a minimum. On the other hand, electroplating has been used for over a century. It is a process which is able to produce a layer of uniform and dense coating that adheres well to the substrate metal, thus modifying the properties of the substrate. It benefits from being relatively low cost and is scalable. Silver is electroplated onto stainless steel threaded compression fittings to prevent galling. Traditional silver electroplating, which contains the use of cyanide as a complexing agent in the electroplating bath, is still in use within industry, even to this day. Cyanide, in its various forms can be poisonous, toxic and even lethal, which presents a risk during the silver electroplating process. Furthermore, the toxic wastes created during the cyanide silver electroplating process are detrimental to the environment. The aim of this work is to develop a self-lubricating non-cyanide silver PTFE composite coating suitable for use in threaded compression fittings of the ferruled type. The composite can be considered self-lubricating when a concentration of 8% or more by volume of the self-lubricating PTFE substance is incorporated. My original contribution to knowledge is firstly the successful development and characterisation of a self-lubricating non-cynanide Ag-PTFE coating on stainless steel without a strike resulting in improved CoF of 0.06 from the CoF of 0.6 based on an unlubricated surface. Secondly is the application of a non-cyanide Ag-PTFE MMC for threaded compression fittings. Thirdly is the characterisation of the make-up process of threaded compression fittings through the proposed use of the torque-angle slope in assessing coating performance for threaded compression fittings during make-up. Conclusions that can be drawn for the work are that the performance non-cyanide Ag-PTFE coating exceeded the performance of the pure Ag coating made using the same non-cyanide process. Moreover, the performance of the Ag-PTFE coating shows promising results when compared to the performance of the commercial silver cyanide coating. As a viable replacement to the current silver cyanide process, the self-lubricating non-cyanide Ag-PTFE coating, will improve the working conditions and have a positive contribution to the environment. Moreover, a thinner coating with has the potential to reduce raw material usage and electroplating waste disposal costs.

Lubrificantes são produtos gasosos, líquidos, semi sólidos ou sólidos (pó) que formam um filme entre duas partes evitando o atrito. Lubrificantes de alto desempenho são designados para trabalharem em condições severas de temperatura, pressão e contaminação. Os mais utilizados são os líquidos (óleos) e semi sólidos (graxas). As graxas são aplicadas aonde o óleo pode escorrer e em pontos de difícil acesso e são divididas basicamente em duas classes, sabão e não sabão. A graxa não sabão mais utilizada é a poliuréia, obtida pela reação entre aminas e isocianato, possui elevada tixotropia, alta rigidez dielétrica e excelente poder anticorrosivo, por isso é amplamente utilizada para lubrificação de motores elétricos e maquinário naval. Para obter uma graxa com altíssimo desempenho, nesse estudo foi utilizado o fluido lubrificante sintético polialfaolefina e também foi empregado o aditivo lubrificante sólido politetrafluoroetileno (PTFE) por apresentar o menor coeficiente de atrito conhecido, é comercialmente encontrado irradiado em ar para obter partículas menores e produzir grupos terminais oxigenados que são mais compatíveis com a superfície metálica. Os ensaios foram realizados de forma comparativa usando a graxa de poliuréia pura e aditivada com PTFE. As caracterizações foram feitas por espectroscopia de infravermelho, análise elementar de C, N, e H e índice de NCO livre, comprovando a formação de poliuréia de quatro carbonos (tetrauréia). As propriedades funcionais de ponto de gota e separação de óleo mostraram alta compatibilidade e estabilidade entre os polímeros, que aumentaram quando foi adicionado PTFE. A excelente resistência da graxa de tetrauréia pura ao desgaste e extrema pressão foram demonstradas pelo teste de quatro esferas e teste prático em rolamentos, caracterizando esta graxa como de alto desempenho quando comparada com as graxas mais utilizadas no mercado. / Lubricants are gaseous, liquid, semi solid or solid (powder) materials those form a film between two parties preventing friction. High performance lubricants are designed to work under severe conditions of temperature, pressure, and contamination. The most used are liquids (oils) and semi solids (greases). Greases are applied where oils can drain or in inaccessible places and are divided generally into two classes, soap and no soap. The most used non soap grease is polyurea, obtained by the reaction between amine and isocyanate, has highly thixotropic, high dielectric strength and excellent anticorrosive property, so it is widely used for lubrication of electric motors and shipbuilding machinery. For a grease with high performance, in this study was used a synthetic lubricant fluid, polyalphaolefin, and was also employed solid lubricant additive polytetrafluoroethylene (PTFE) due its lowest coefficient of friction, is found commercially irradiated in air to obtain smaller particles and to produce oxygenated terminal groups those are more compatible with the metal surface. The tests conducted were comparatively between pure polyurea grease and with PTFE additive. The characterizations were made by infrared spectroscopy and elemental analysis of C, N and H and Free NCO index, proving the formation of four carbons polyurea (tetraurea). The functional analysis of drop point and oil separation showed high stability and compatibility between the polymers increased when PTFE was added. The excellent resistance of pure tetraurea grease to wear and extreme pressure were demonstrated by four-ball and practical bearings tests, characterizing this grease as a high performance lubricant, when compared to most used greases in the market.

Les polymères sont de plus en plus répandus dans différents secteurs industriels comme une alternative aux métaux. En effet, les composants en polymère permettent une réduction accrue du poids et une meilleure inertie chimique dans les structures où ils sont utilisés. Ils permettent également une réduction du frottement sans recourir à des systèmes de lubrification externe. Parmi ces polymères, le PTFE - connu sous le nom du Teflon et découvert en 1938 - se caractérise par une morphologie semi-cristalline particulière où les molécules de PTFE forment des superstructures dites « à bandes ». Il possède d’excellentes propriétés thermiques, un très faible coefficient de frottement et une très bonne inertie chimique justifiant sa vaste utilisation dans différentes applications : comme renfort de type lubrifiant solide, revêtement antiadhésif, isolant électrique des câbles dans le domaine de l’aéronautique, récipients pour des produits chimiques réactifs. Ce travail de thèse s’inscrit dans ce contexte et adopte une démarche tribologique globale. Il étudie les réponses tribologiques d’un contact PTFE/Ti-6Al-4V sollicité en fretting-usure alternatif - notamment en mode glissement total et reciprocating - dans une configuration cylindre/plan. Les paramètres étudiés sont : nombre de cycles, vitesse de glissement, force normale et propriétés thermomécaniques et surfaciques des matériaux. Cette étude propose de nouvelles formalisations analytiques basées sur l’approche d’Archard et établit des lois de frottement et d’usure qui intègrent les effets de ces paramètres. Le rôle joué par le film de transfert dans la détermination des réponses tribologiques est également mis en évidence. / The tribology of thermoplastic polymers is nowadays one of the major issues in several engineering fields. These non-metallic materials increasingly provide a useful alternative to metals that are in contact with a harder counterface. Areas of application are various and include offshore oil-drilling, aeronautics and the automotive industry and biomedical applications such as prosthesis designs. The aim of polymer-metal, and especially PTFE/Ti-6Al-4V, designs is to reduce wear and friction. Polytetrafluoroethylene (PTFE) is one such interesting thermoplastic polymer that has been closely studied since it was discovered in 1938. It is a high-performance engineering polymer characterized especially by a high melting point, chemical inertness and low coefficient of friction due to its banded structure. PTFE is a tribologically attractive material, widely used especially as a solid lubricant in a variety of dry sliding tribosystems. The purpose of this study is to evaluate friction and wear rate evolution for gross slip fretting-reciprocating sliding conditions of PTFE/Ti-6Al-4V interface in a cylinder/plane configuration. Various investigations have been made to study the influence of wear test conditions: number of cycles, sliding speed, normal force, materials thermomechanical and surface properties. Analysis aimed to determine tribological processes as well as formulation of experimental evolution of friction and wear rates regarding selected parameters. Finally, characterization of the transfer film formed on the counterpart under repeated cyclic sliding is undertaken to determine its role and its interference with wear and friction response.