Ce travail de thèse est consacré à l’étude du vieillissement UV d’un caoutchouc EPDM (éthylène propylène diène monomère) avec une attention spéciale sur les additifs du système de vulcanisation. Pour cela nous avons utilisé des techniques particulièrement adaptées à l’analyse de surface telles que le ToF-SIMS, l’XPS, l’ATR-FTIR, le MEB-EDX et l’AFM. Dans un premier temps nous avons pu déterminer la composition chimique de la surface du caoutchouc EPDM vulcanisé à l’état initial. Nous avons pu identifier les sous-produits de vulcanisation et déterminer de manière qualitative leur répartition en surface. Les profils en profondeur ToF-SIMS ont permis de mettre en évidence une couche d’enrichissement en additifs à le surface du caoutchouc dont l’origine pourrait provenir de leur migration par cristallisation ou « effet bloom » par vulcanisation. Dans la seconde partie, nous avons étudié l’effet du vieillissement artificiel SEPAP sur le caoutchouc et sur les additifs. Nos résultats montrent que la surface du caoutchouc ainsi que les deux accélérateurs de vulcanisation, le MBTS (2,2’-Dithiobis(benzothiazole)) et le ZBPT (Zinc O, O-Dibutylphosphorodithioate) subissent des changements chimiques et morphologiques profonds caractérisés par une oxydation chimique et une dégradation structurale. Les études cinétiques ont montré que les changements chimiques les plus importants étaient observés pendant les 100 premières heures. Nous avons examiné un caoutchouc industriel, actuellement utilisé dans l’étanchéité de carrosserie, afin de mieux comprendre le comportement des agents de mise en oeuvre à l’état initial et au cours du vieillissement. Ces agents de mise en oeuvre jouent un rôle clé dans la composition chimique du caoutchouc à l’état initial malgré la faible quantité incorporée. Nous avons montré que ces composés recouvrent la surface et forment une couche épaisse d’environ 500 nm, très résistante au vieillissement. / This thesis is devoted to the study of UV aging of an EPDM rubber with particular emphasis on additives involved invulcanization. For this purpose, we use techniques suitable for surface analysis such as ToF-SIMS, XPS, ATR-FTIR, SEMEDXand AFM. We first determine the initial chemical composition of the surface of the EPDM rubber. We identify the by-products of vulcanization and qualitatively determine their distribution on the surface. The ToF-SIMS depth profiles exhibit a layer enriched in additives on the surface of the rubber due to migration by crystallization or by the “bloom effect” after vulcanization. In addition, images from 3D profiles show that some of these additives are adsorbed on the no-black fillers. In the second part, we study the effect of artificial aging on the rubber and the additives. Our results indicate that both the surface of the rubber and the two rubber accelerators, MBT and ZBPT, undergoes significant chemical and morphological changes characterized by chemical oxidation and structural degradation. Our Kinetic studies show that the most important chemical changes take place during the first 100h. The final chapter is devoted to the study of industrial rubber, currently used in vehicle body seals, and discusses on understanding of the behavior of the processing agents in the initial state and during aging. These agents play a key role in the chemical composition of the rubber in the initial state, despite the small amounts incorporated. We show that these compounds cover the surface and form a layer about 500 nm thick, very resistant to aging.

ABSTRACT PHOTO-OXIDATIVE DEGRADATION OF ABS COPOLYMER G&uuml / zel, Aylin M.S., Department of Polymer Science and Technology Supervisor: Prof. Dr. Teoman Tin&ccedil / er Co-Supervisor: Prof. Dr. Cevdet Kaynak September 2009, 55 pages Acrylonitrile-butadiene-styrene (ABS) polymer is one of the most popular copolymer having an elastomeric butadiene phase dispersed in rigid amorphous styrene and semi-crystalline acrylonitrile. Due to double bonds in the polybutadiene phase, ABS copolymers are very sensitive to photo-oxidative degradation. Photo-oxidation of butadiene rubber phase results in the formation of chromorphores and these chromorphores act as initiators in photo-oxidative degradation and after a while ABS starts yellowing. In this work, the relationship between the UV light and the yellowing of ABS samples was also investigated with respect to time. In this study, pure, light stabilized and commercial ABS samples were aged under UV light. As the UV light intensity increased from 800 to 2800 &amp / #61549 / W/cm2, yellowing of the samples were increased for pure ABS. This increase in yellowing of the samples was about 27 times higher compared to lower energy. In this study, UV stabilizers IRGANOX 1076 (sterically hindered phenolic antioxidant), IRGAFOS 168 (hydrolycally stable phosphite stabilizer) and TINUVIN P (hydroxyphenol benzotriazole) were used alone or in combination with each other. Pure ABS samples, commercial ABS samples and UV stabilized ABS samples were aged under the same UV light. UV aging degradation was followed by measuring the yellowness of the samples at certain time intervals. Yellowness of the samples was followed by using Coloreye XTH Spectrometer. Degradation in ABS, however, was followed by using FTIR with an increase in the peak area of carbonyl groups in the ABS matrix. Both color analysis and the FTIR analysis showed that combination of the IRGANOX 1076 and IRGAFOS 168 stabilizers gave the best stabilization. This revealed that combination of phenol and phosphate containing stabilizer is the most useful combination to prevent photo-oxidative degradation of ABS copolymer. Additionally, vegetable oil was applied to the surface of a new set of ABS samples and these samples were aged for 700 h. Yellowing tendency of these samples was compared with the yellowing tendency of ABS samples that are directly aged for 500 h. It was clearly observed that samples with oil smeared had more resistance to UV radiation with respect to others. This shows that oil acts protective layer to the UV light and oxygen and slow down the photo-oxidative degradation. Lastly some commercial ABS samples were compared to each other with respect to their yellowing tendency. Commercial ABS samples coded as K, L, A, B, C and D were aged under UV light at about 500 h. Sample A showed the best resistance against the yellowing among the other commercial ABS samples.

Dimethacrylate oligomers diluted with styrene reactive diluents (so-called vinyl ester resins) are becoming increasingly important for composites in applications such as transportation vehicles, printed wiring boards and civil infrastructure. This research has focused on the generation and comparative analysis of glassy dimethacrylate networks as a function of oligomer structure, the type of reactive diluent, composition and curing conditions. A novel cycloaliphatic dimethacrylate was synthesized and its networks were compared to oligomeric structures containing dimethacrylates derived from epoxy terminated oligomers (from bisphenol-A and epichlorohydrin). Both types of dimethacrylates co-cured with methyl methacrylate exhibited increases in Mc and fracture toughness as the concentration of methyl methacrylate was increased. By contrast, networks prepared with a styrene diluent displayed reduced toughness with increasing styrene and Mc. Due to the need for long-term composite environmental durability, the effects of moisture and exposure to sunlight are important. Thus, these materials were exposed to ultraviolet light on a rotating drum for 225 days and the exposure was carefully monitored. Initial results from this study suggest that both the networks comprising the aromatic dimethacrylate/styrene structures as well as the cycloaliphatic analogues cured with methyl methacrylate undergo reductions in rubbery moduli upon aging under these conditions. X-Ray photoelectron spectroscopy shows higher levels of oxidation on the bisphenol-A vinyl ester networks cured with styrene, especially those containing dimethylaniline and cobalt naphthenate as accelerators. Scanning electron microscopy indicates a smooth surface for the cycloaliphatic networks cured with methyl methacrylate and a pitted surface for the aromatic networks cured with styrene. Water absorption is also higher for the cycloaliphatic vinyl ester; however, curing with a longer alkyl chain methacrylate (butyl methacrylate) decreases the water absorption to levels comparable to those cured with styrene. / Ph. D.

[pt] Ao contrário dos mecanismos tradicionais, um mecanismo flexível conta com a deflexão de seus membros flexíveis para gerar movimento, ao mesmo tempo que apresenta vantagens como a desnecessidade de lubrificação e uma montagem mais fácil. Um mecanismo flexível de mola orto-planar foi analisado neste trabalho e seu desempenho mecânico após testes de envelhecimentos higrotérmicos e com radiação ultravioleta foram estudados. A análise do envelhecimento aqui realizada aborda o desempenho de mecanismos flexíveis após processos de envelhecimentos que pdoe ajudar no desenvolvimento de futuros mecanismos flexíveis. Amostras de tração ASTM D638 tipo I também foram submetidas aos envelhecimentos para servir de comparação para as amostras de mola orto-planar. As amostras foram submetidas a três tipos diferentes de envelhecimento, a saber: imersão em água, imersão em óleo e radiação ultravioleta. Os testes de envelhecimento por imersão em líquido foram realizados em três níveis de temperaturas: temperatura ambiente, 50 graus C e 70 graus C. Em geral, as amostras de tração mostraram mudanças estatísticas significativas no módulo de Young e no deformação na ruptura, enquanto as amostras de mola orto-planar não apresentaram alterações estatísticas importantes em nenhuma condição de envelhecimento, o que indica que as propriedades mecânicas e capacidades elásticas dos mecanismos não foram afetadas pelos processos de envelhecimento. Embora mais testes com os materiais específicos, ambiente e tempo de exposição sejam necessários para verificar o uso em uma aplicação específica, os resultados deste estudo sugerem que os mecanismos flexíveis mostram a promessa de uso em aplicações onde o envelhecimento é uma preocupação e sua vida é esperada estar dentro dos limites deste estudo de envelhecimento. / [en] In contrast to traditional mechanisms, a compliant mechanism relies on the deflection of its flexible members to generate motion, while presenting advantages such as no need for lubrication and easier assembly. An ortho-planar spring (OPS) compliant mechanism was analyzed in this work and its mechanical performance after hygrothermal and ultraviolet radiation aging tests was studied. The aging analysis performed here addresses the performance of compliant mechanisms after aging processes that can help in the design of future compliant mechanisms. ASTM D638 tensile test type I samples were also subjected to aging to serve as a comparison for OPS samples. The samples were subjected to three different types of aging conditions, namely water immersion, oil immersion and ultraviolet radiation. The liquid immersion aging tests were performed in three temperature levels: room temperature, 50 C degrees and 70 C degrees. In general, tensile samples showed significant statistical changes in Young s modulus and elongation at break, while OPS samples did not present considerable statistical change in any aging condition, which indicate that the mechanical properties and elastic capabilities of OPS samples were not affected by aging processes. Although more testing with the specific materials, environment, and exposure time would be required to verify its use in a specific application, the findings of this study suggest that compliant mechanisms show promise for use in applications where aging is a concern, and their life is expected to be within the limits of this aging study.