The thermo-oxidative degradation of unstabilized polyamide 6 (PA-6) was investigated by a number of novel techniques in an attempt to achieve a better understanding of the mechanisms involved in the oxidative degradation of polymers. Particular attention was given to the influence of end groups on PA-6 oxidation by studying samples that terminated predominantly in carboxylic, amine or methyl end groups. The changes occurring in the oxidative stabilities and mechanisms of PA-6 as a result of altering the end groups of PA-6 were investigated by a technique termed CL-DSC, which simultaneously measures the chemiluminescence (CL) and heat flow (DSC) from a sample. When amine end groups were abundant in the PA-6 sample a chemically induced electron exchange luminescence (CIEEL) mechanism could occur directly and the CL intensity was proportional to the heat flow curve of the DSC. However, when amine end groups were absent it was the first derivative of the CL intensity that was proportional to the heat flow curve because the CIEEL mechanism could not operate until an easily oxidisable luminescent oxidation product was formed. Due to the dramatic effect end groups have on the oxidation mechanisms of PA-6 it was hypothesized that end groups could be sites analogous to the impurities in polyolefins that lead to heterogeneous oxidation. To test this hypothesis, CL Imaging was used to map the occurrence and extent of oxidation across samples of PA-6 to display the influence end groups have on the homogeneous or heterogeneous nature of PA-6 oxidation. Sequences of FTIES spectra collected at specified time intervals during the in situ oxidation of PA-6 samples terminating in the different end groups were turned into oxidation product profiles. The differences between spectra related to significant points on the oxidation profiles were compared in an attempt to elucidate the chemical or physical changes occurring in the samples during oxidation. To identify the species involved in the mechanistically different oxidation processes resulting from the different end groups, methods for the MALDI-TOF analysis of non-oxidized and oxidized PA- 6 samples were developed via trial and error. It was only possible to detect the occurrence of degradation products by MALDI-TOF MS after considerable oxidation as measured by chemiluminescence, by which time the species were the result of a number of oxidative processes. Therefore, identification of the species formed was not possible.

No description available.

Les besoins en électronique de puissance, de plus en plus exigeants, ont motivé des recherches à l'échelle mondiale sur d'autres matériaux tels que le diamant comme remplaçant du silicium. Nos travaux de recherche sont plus spécifiquement axés sur la définition et la qualification de matériaux polymères capables de garantir l'intégrité des fonctions physiques de modules de puissance en environnement sévère. L'étude concerne la durabilité de candidats polymères à retenir pour le boîtier dont l'objectif est de protéger l'interrupteur de l'environnement extérieur. Suite aux choix des différents polymères étudiés, variables dans leur chimie et leur morphologie (amorphe ou semi-cristallin), un premier objectif scientifique est alors de chercher les relations structures/propriétés permettant de contrôler le procédé de mise en forme des polyimides semi-cristallins et d'en déduire les conditions requises à l'obtention de performances optimisées. Un second objectif a concerné la tenue des différents matériaux sélectionnés en vieillissements isothermes thermo-oxydatifs. / Requirements in power electronics are more and more demanding about materials behavior in their operating conditions. This has motivated global scale researches about other materials replacing silicon such as diamond. This study is specifically focusing on the definition and qualification of polymer materials which could preserve physical functions of power modules in severe environments. This study focuses on the durability of several polymers used for the case. This later allows to protect the chip from external environment. The choice of different studied polymers which are dissimilar in chemistry and morphology (i.e. amorphous or semicrystalline) has been made in this study. Then, a first scientific goal was to search the structures/properties relations leading to the control of the manufacturing process of semicrystalline polyimides. A second goal concerned the mechanical strength evaluation of selected materials after thermo-oxidative isothermal ageing.

No description available.

No description available.

Traditional fluorosilicones contain a siloxane backbone and pendant fluorinated group leading to low temperature ductility and excellent thermal stability. However, acidic or basic catalysts can reduce the thermal stability from a potential 350 °C to 150 °C. The predominant decomposition mechanism is through chain scission and it is hypothesized that preventing this will result in polymers with higher thermal stability. Three approaches were taken to prevent chain scission. First, a series of hybrid fluorosilicones based on (trifluorovinyl)benzene were synthesized through condensation polymerization with initial decomposition temperatures of approximately 240 °C. These were compared to similar aromatic polyethers and removal of the ether oxygen lowered the initial decomposition temperature by approximately 190 °C demonstrating the importance of this oxygen to the stability of polyethers. Second, reverse fluorosilicone (fluorinated backbone and pendant siloxane) terpolymers of chlorotrifluoroethylene (CTFE), vinyl acetate (VAc) and methacryloxypropyl-terminated polydimethylsiloxane (PDMSMA) were synthesized in supercritical CO2 (scCO2) or by emulsion polymerization. Chain scission was prevented as initial decomposition occurred between 231 and 278 °C. In both the emulsion and scCO2 cases, VAc was essential in facilitating cross-propagation between CTFE and PDMSMA and the branching was similar suggesting polymerization media does not affect polymer structure. Emulsion-based polymers had higher molar masses and thermal stability whereas comparable scCO2 polymers had higher yields and incorporated more PDMSMA. Third, a series of homo-, co-, and terpolymers of CTFE, VAc and methacryloxypropyl-terminated silsesquioxane (POSSMA) were synthesized representing the first synthesis of POSSMA containing polymers in scCO2 and demonstrating reverse fluorosilicones can be synthesized without VAc. Chain scission was prevented as initial decomposition occurred from 244 to 296 °C with thermal stability increasing with CTFE content to a limit. Decomposition of the polymers was examined and mechanism elucidated. In air, the copolymers give 40 to 47 wt% char since the silsesquioxane oxidizes to SiO2 while in N2, no residue is seen. In contrast, the terpolymers give a carbonaceous residue of approximately 20 wt% in N2. The flammability and surface properties of the polymers were examined with the terpolymers having flammability similar to p(CTFE) and surface properties comparable to p(POSSMA) giving a low-flammability, hydrophobic polymer.

Traditional fluorosilicones contain a siloxane backbone and pendant fluorinated group leading to low temperature ductility and excellent thermal stability. However, acidic or basic catalysts can reduce the thermal stability from a potential 350 °C to 150 °C. The predominant decomposition mechanism is through chain scission and it is hypothesized that preventing this will result in polymers with higher thermal stability. Three approaches were taken to prevent chain scission. First, a series of hybrid fluorosilicones based on (trifluorovinyl)benzene were synthesized through condensation polymerization with initial decomposition temperatures of approximately 240 °C. These were compared to similar aromatic polyethers and removal of the ether oxygen lowered the initial decomposition temperature by approximately 190 °C demonstrating the importance of this oxygen to the stability of polyethers. Second, reverse fluorosilicone (fluorinated backbone and pendant siloxane) terpolymers of chlorotrifluoroethylene (CTFE), vinyl acetate (VAc) and methacryloxypropyl-terminated polydimethylsiloxane (PDMSMA) were synthesized in supercritical CO2 (scCO2) or by emulsion polymerization. Chain scission was prevented as initial decomposition occurred between 231 and 278 °C. In both the emulsion and scCO2 cases, VAc was essential in facilitating cross-propagation between CTFE and PDMSMA and the branching was similar suggesting polymerization media does not affect polymer structure. Emulsion-based polymers had higher molar masses and thermal stability whereas comparable scCO2 polymers had higher yields and incorporated more PDMSMA. Third, a series of homo-, co-, and terpolymers of CTFE, VAc and methacryloxypropyl-terminated silsesquioxane (POSSMA) were synthesized representing the first synthesis of POSSMA containing polymers in scCO2 and demonstrating reverse fluorosilicones can be synthesized without VAc. Chain scission was prevented as initial decomposition occurred from 244 to 296 °C with thermal stability increasing with CTFE content to a limit. Decomposition of the polymers was examined and mechanism elucidated. In air, the copolymers give 40 to 47 wt% char since the silsesquioxane oxidizes to SiO2 while in N2, no residue is seen. In contrast, the terpolymers give a carbonaceous residue of approximately 20 wt% in N2. The flammability and surface properties of the polymers were examined with the terpolymers having flammability similar to p(CTFE) and surface properties comparable to p(POSSMA) giving a low-flammability, hydrophobic polymer.

Made available in DSpace on 2015-05-14T13:21:10Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3821776 bytes, checksum: a79b7372cf49452691bbcd3110625c55 (MD5) Previous issue date: 2011-11-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The evaluation of thermo-oxidative stability is an essential factor for application an of oil in the food industry. In addition, the increase consumption of vegetable oils requires the evaluation of alternative oil sources as feedstock for biodiesel production. This research investigated the thermo-oxidative stability of okra seeds oil (with and without antioxidant) submitted to the Schaal test at 60 °C for 10 days. The oxidation process was evaluated by chemical parameters acidity value (AV), iodine value (IV), peroxide value (PV), extinction value (E) for conjugated dienes, oxidation temperature (OT), induction period (IP) and oxidative induction time (OIT). The results showed that AV and IV values for oil samples with (OQT) and without (OQ) the antioxidant tert-butyl hydroquinone (TBHQ) do not changed after aging in oven. However, OQT samples showed lower PV value, higher IP and OIT values than OQ samples hence high oxidative stability. IP and OIT value for OQT samples remained constant as function of time under heating in oven. Differently OQ samples presented decreasing IP and OIT values and increasing IP value. Regarding to E value it remained constant for OQT samples and increased around 35 % for OQ samples. The increased value of E is an indication that there was formation of conjugated dienes in samples without antioxidant. These data demonstrated the importance of adding antioxidants to protect oil from oxidative degradation. Another parameter used for the purpose of evaluate the oxidative stability of oil has been monitoring the absorption bands in the infrared region, characteristic of oxidation products. Evaluation of infrared spectra of the OQ samples do not show changes in intensity or shifting in the bands that are altered with the decomposition of hydroperoxides formed in heating test. Through thermogravimetric analysis it was determined that the onset temperature decomposition (Tonset) okra oil was higher than for olive, sunflower, canola, soybeans and corn oils. This parameter shows more stability to the okra oil and it was attributed to the fatty acid composition of this oil. Fatty acid composition indicated predominance of linoleic acid (33.5 %) followed by palmitic acid (25.2 %) and oleic acid (19.3 %). It was found that content of linoleic acid, an acid more susceptible to oxidation, is lower when compared with soybean, sunflower and corn oils. It also gives a value of saturated fatty acids (33.4 %) higher than these edibles oils. The results obtained in this study showed that okra seeds oil has good thermal and oxidative stability, and an indication of its use as edible oil and potential source of feedstock for biodiesel. / A crescente demanda por óleos vegetais criou a necessidade de se avaliar fontes oleaginosas alternativas para suprir esta procura. Como a oxidação é um fator crítico inerente aos óleos vegetais, este trabalho visou contribuir com dados de estabilidade térmica e oxidativa do óleo de quiabo, ainda não explorado comercialmente. Esta pesquisa investigou a estabilidade termooxidativa de amostras do óleo das sementes de quiabo, aditivadas ou não com o antioxidante terc-butil-hidroquinona (TBHQ), submetidas ao teste de Schaal a 60 oC por 10 dias. O processo oxidativo foi avaliado pelos parâmetros químicos índice de acidez (IA), índice de iodo (II), índice de peróxido (IP), absortividade específica (E), período de indução (PI), tempo de indução oxidativa (OIT) e temperatura de oxidação (OT). Os resultados mostraram que o valor de IA e II para amostras de óleo com e sem TBHQ, codificadas respectivamente OQT e OQ, não sofreu alteração após envelhecimento em estufa. No entanto, as amostras OQT apresentaram menor valor de IP e maior valor de PI e OIT do que as amostras OQ, mostrando maior estabilidade oxidativa. O valor de PI e OIT das amostras OQT se manteve constante em função do tempo sob aquecimento em estufa, diferentemente das amostras OQ, que apresentaram valor de PI e OIT decrescente e IP crescente. Com relação ao valor de E, este se manteve constante para as amostras OQT e aumentou em torno de 35 % para as amostras OQ. O aumento do valor de E foi um indicativo que houve a formação de dienos conjugados nas amostras sem antioxidante. Outro parâmetro utilizado na avaliação da estabilidade oxidativa do óleo de quiabo foi o monitoramento de bandas de absorção na região do infravermelho (IV), características de produtos da oxidação. Nos espectros de IV das amostras OQ e OQT não foram observadas mudanças na intensidade ou deslocamento nas bandas que podem sofrer modificações com a decomposição dos hidroperóxidos formados durante o teste de estufa. A temperatura onset de decomposição (Tonset) do óleo das sementes de quiabo, determinada por análise termogravimétrica, foi maior que para os óleos de girassol, soja e milho. Este parâmetro demonstrou maior estabilidade para o óleo de quiabo, fato atribuído à composição de ácidos graxos deste óleo. A composição em ácidos graxos, determinada por cromatografia gasosa acoplada ao espectrômetro de massa, indicou predominância do ácido linoléico (33,5 %), seguido do ácido palmítico (25,2 %) e ácido oléico (19,3%). O teor de ácido linoléico, um dos ácidos mais susceptíveis à oxidação, foi menor quando comparado com os óleos de soja, girassol e milho e o teor de ácidos graxos saturados (33,4 %) foi maior que para estes óleos comestíveis. O conjunto de resultados obtidos mostrou que o óleo das sementes de quiabo apresentou boa estabilidade térmica e oxidativa, sendo um indicativo de seu uso como óleo comestível e possível fonte de matéria-prima para biodiesel.

Made available in DSpace on 2015-05-14T13:21:50Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2232286 bytes, checksum: 71edf4709cd41125651e3890fba4065b (MD5) Previous issue date: 2009-05-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present work aims at investing the biodiesel obtained from the transesterification of sunflower oil by means of alkaline catalysis using 30% of ethyl alcohol, 1% KOH for each 100g of oil and (1:6) oil/alcohol molar ratio. The overall content of ethyl esters (99.72%) was determined by gas chromatography coupled to mass spectrometer, confirm the efficiency of the purification process carried out after the biodiesel synthesis. In the physico-chemical analyses, the results obtained complied with the standards allowed by the Technical Regulation No. 7 from the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP). Thermal analyses were carried out with sunflower oil, diesel, sunflower ethanol biodiesel (B100) and its biodiesel/diesel blends, with proportion of 5, 15, 20, 25 and 50% biodiesel, employing the heating rate of 10 °C.min-1 in atmospheres of air and nitrogen, with runs up to 600 °C. The thermal decomposition of the samples was studied from the TG curves, aiming at assessing the order of thermal stability of the samples. The antioxidants α-tocopherol, BHT and TBHQ were added to the biodiesel samples aiming at assessing their efficiency in improving the thermo-oxidative stability of biodiesel. The techniques of pressure differential scanning calorimetry (PDSC) and Rancimat, revealed that the most indicated antioxidants for the storage of the ethanol sunflower oil biodiesel are BHT and TBHQ. However, even showing an antioxidant activity when added to the ethanol sunflower oil biodiesel, BHT was not efficient enough to increase the induction period to the minimum value of 6 hours at 110 ºC, as determined by ANP. The kinetic parameters of activation energy (Ea) and pre-exponential factor (A) were determined utilizing the Arrhenius equation, from data obtained in the isothermal thermogravimetric curves. / O presente trabalho buscou investigar o biodiesel. O mesmo foi proveniente da transesterificação do óleo de girassol, via catálise básica, utilizando-se 30% de álcool etílico, 1% de KOH para cada 100 g de óleo, razão molar óleo/álcool (1:6). O teor total de ésteres etílicos de 99,72% determinado na cromatografia gasosa acoplada a espectroscopia de massa, confirma a eficiência do processo de purificação após a síntese do biodiesel. Nas análises físico-químicas, os resultados obtidos estavam dentro dos limites permitidos pelo Regulamento Técnico nº 7 da Agência Nacional do Petróleo, Gás Natural e Biocombustíveis. As análises térmicas foram realizadas com o óleo de girassol, diesel, biodiesel etílico de girassol (B100) e suas misturas biodiesel/diesel nas proporções 5, 15, 20, 25 e 50%, na razão de aquecimento de 10 °C.min-1 em atmosferas de ar e nitrogênio, com aquecimento até 600 °C. Foram observadas as decomposições térmicas, das curvas termogravimétricas para verificar a ordem de estabilidade térmica. O estudo da adição dos antioxidantes α-tocoferol, butil-hidroxi-anisol (BHT) e t-butil-hidroquinona (TBHQ) no biodiesel foi realizado com o intuito de verificar a eficiência dos mesmos diante da sua estabilidade oxidativa. A Calorimetria Exploratória Diferencial Pressurizada (PDSC) e o Teste de Estabilidade Oxidativa Acelerada (Rancimat, Método EN 14112) revelaram que os antioxidantes mais indicados para o armazenamento do biodiesel etílico de girassol são o BHT e o TBHQ. Entretanto, ainda exercendo atividade como oxidante quando acrescido ao biodiesel etílico de girassol, o BHT não foi eficiente em elevar o período de indução a um valor mínimo de 6 h a 110 ºC, estabelecida pela ANP. Foram determinados os parâmetros cinéticos: energia de ativação (Ea) e o fator pré-exponencial (A), utilizando a equação de Arrhenius, a partir dos dados obtidos das curvas termogravimétricas isotérmicas.

Le caoutchouc naturel présente une très bonne résistance à la propagation de fissure. Cette particularité est généralement attribuée dans la littérature à sa capacité à cristalliser sous déformation. A ce jour, l'essentiel des travaux dans ce domaine porte sur des échantillons réticulés par une vulcanisation dite efficace, c’est-à-dire dont les noeuds de réticulation sont principalement composés de ponts monosulfures. Pour certaines applications, et parce qu’elle est réputée conduire à de meilleure propriétés en fatigue, il est intéressant d'utiliser une vulcanisation dite conventionnelle. Le matériau est alors composé majoritairement de ponts polysulfures. Le phénomène de cristallisation sous déformation, exacerbée en pointe de fissure en raison d'une amplification du champ de déformation, semble être l'un des mécanismes responsables de l'accroissement de la durée de vie en fatigue du matériau vulcanisé de manière efficace. Cependant, sur matériaux vulcanisés de manière conventionnelle et thermo-oxydés (77°C), cette corrélation doit être confirmée en raison d’une évolution importante de l'architecture du réseau élastomère pendant son vieillissement pouvant en effet avoir un impact important sur la capacité du matériau à cristalliser sous déformation. Cette étude se propose donc de caractériser l’évolution de réseaux élastomères vulcanisés de manières conventionnelles pendant leur vieillissement thermo-oxydant, puis d’évaluer leur résistance à la propagation de fissure à différents niveaux de déformation macroscopique. Des analyses in situ WAXS sous rayonnement synchrotron en fond de fissure permettent alors de relier ces résultats à l'évolution de l’aptitude de ces matériaux à cristalliser sous déformation. / Natural rubber (NR) is largely used in the tire industry due to its excellent mechanical properties, e.g. its very good resistance to fatigue crack growth at high strain. It is generally accepted that this outstanding behavior is related to its ability to crystallize under strain. Such phenomenon, so called SIC, strongly depends on parameters like temperature, strain rate as well as the architecture of the rubber network. The microstructure of this network is formed during the crosslinking process and depends on the vulcanization system, i.e. “Efficient” or “Conventional”. The former vulcanization recipe consists in the formation of short or monosulfide bridges in the elastomer network whereas the latter (necessary to ensure a good adhesion between metallic and rubber parts in a tire) will mainly create longer polysulfide bridges. During its life, the tire will be submitted to a slow aerobic ageing which will cause structural modifications of the initial network and therefore an evolution of the rubber ability to crystallize under strain and to resist against crack propagation. In general, the structural modifications are caused by complex chemical mechanisms, highly sensitive to temperature, leading to chain scission and chain crosslinking. They can also involve sulfur bridge reorganization when NR is conventionally vulcanized. Nevertheless, most of the literature on NR ageing has been performed on efficiently cross-linked NR, and in thermal conditions which are much too severe to be representative of the material ageing in tire applications. Within this frame, our objective is to study this material when it is aged at 77 °C in air. Such parameters have been identified as capable of reproducing more realistically and over a reasonable duration, the ageing of rubber in some use conditions. After characterization of the evolution of the aged materials microstructure, their crack propagation resistance will be studied at 0.01 Hz for different values of macroscopic deformations. Time resolved Wide Angle X-ray scattering (WAXS) measure-ments, carried out at room temperature, will then provide information on the crystallization process around the crack tip. Based on these results, the relation between the network evolution during ageing, the fatigue properties and the ability to strain crystal-lize in such conditions will be established in this work.