De modo geral, os ciclos de cura para resina epóxi demandam algumas horas e elevadas temperaturas. Em busca de novas soluções para a otimização de processos sem perda de qualidade, bem como a economia de energia, diversos processos de cura de resina epóxi não convencionais foram desenvolvidos ao longo dos anos. O uso de irradiação de micro-ondas teve início após a Segunda Guerra Mundial, com a invenção do RADAR. A radiação de micro-ondas é uma radiação não-ionizante, com bom poder de penetração e boa transferência de calor em materiais absorvedores, ou materiais com cargas absorvedoras. A frequência usualmente utilizada em trabalhos de pesquisa e desenvolvimento é de 2,45GHz, a mesma disponível nos equipamentos comerciais e industriais existentes. Para a cura de resinas epóxi não são necessárias alterações no sistema reativo, com iniciadores específicos sensíveis a micro-ondas. O \"efeito micro-ondas\" proporciona um aumento da velocidade de colisão entre os reagentes que, associada à energia absorvida pelo sistema reacional, acelera a reação de cura, possibilitando a cura de resinas de tempo de uso longo (superior a 24 horas, em temperatura ambiente) em questão de minutos. Neste estudo foi utilizado inicialmente um sistema epóxi do tipo DGEBA, com endurecedor à base de anidrido e acelerador à base de amina, nas mesmas condições comerciais indicadas pelo fabricante. Testes iniciais com os fornos de micro-ondas selecionados foram realizados previamente a operação com sistemas epóxi. A cura do sistema já catalisado foi realizada em dois diferentes fornos de micro-ondas adaptados para uso em laboratório. A temperatura de degradação, e a temperatura de transição vítrea, foram avaliadas por técnicas de análise térmica. Cargas, pigmentos e aditivos também foram avaliados, no sentido de determinar suas influências em misturas com o sistema epóxi escolhido. Após estudos preliminares com o sistema epóxi puro, foram realizados testes em compósitos reforçados com fibra de vidro. Os resultados indicam que o processo é promissor, correspondendo ao observado em diversos artigos na literatura. / Generally, the cure cycles epoxy resin demand for few hours, and elevated temperatures. In search of new solutions for process optimization without loss of quality as well as energy saving, various processes of curing epoxy resin unconventional were developed over the years. The use of microwave irradiation began after World War II, with the invention of RADAR. The microwave radiation is non-ionizing radiation, with good power of penetration and good heat transfer in absorbing materials, or materials with absorbing fillers. The frequency usually used in research and development is of 2.45 GHz, the same is available in commercial equipment. For curing epoxy resins are not necessary changes in the system reactive with specific initiators sensitive to microwaves. The \"microwave effect\" provides increased on collision velocity between the reactants, which combined with energy absorbed by the reaction system, its accelerates the reaction curing, allowing the resin to cure long pot-life (times greater than 24 hours) in minutes. In this study, a DGEBA epoxy resin with an anhydride based hardener, and an initiator based on amine was used under the same conditions indicated by the manufacturer. Preliminary tests with the microwave ovens selected were executed before the operation with epoxy systems. The curing of the catalyzed system was performed in two different adapted microwave ovens for use in laboratory. The degradation temperature and the glass transition temperature were evaluated by thermal analysis techniques. Fillers, pigments and additives also were evaluated to determinate the influences with and without the epoxy system. After previous tests with the epoxy system alone, it was realized tests in composites form with glass fiber. The initial results indicate that the curing process by microwave irradiation is promising, and corresponding with the literature.

No description available.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της επίδρασης της θερμικής κόπωσης στη μηχανική συμπεριφορά κοκκωδών συνθέτων υλικών πολυμερικής μήτρας ενισχυμένης με κόκκους ελαιοπυρήνα υπό μορφή σκόνης. Τα σύνθετα υλικά που κατασκευάσθηκαν μελετήθηκαν πειραματικά και τα αποτελέσματα αναλύθηκαν και προβλέφθηκαν θεωρητικά. Αρχικά πραγματοποίηθηκε η κατασκευή των συνθέτων υλικών σε διάφορες περιεκτικότητες σε κόκκους ελαιοπυρήνα. Από τον μηχανικό χαρακτηρισμό με στατικά πειράματα κάμψης τριών σημείων όλων των συνθέτων υλικών που κατασκευάστηκαν, διαπιστώθηκε η ενισχυτική ικανότητα του ελαιοπυρήνα σε μορφή σκόνης όταν αυτή χρησιμοποιείται ως υλικό ενίσχυσης για την κατασκευή συνθέτων υλικών. Ενώ, στη συνέχεια μελετήθηκε και η επίδραση της θερμικής κόπωσης στη μηχανική συμπεριφορά των συνθέτων υλικών που κατασκευάστηκαν. Τέλος, εφαρμόστηκαν δύο διαφορετικά μοντέλα πρόβλεψης του μέτρου ελαστικότητας συναρτήσει της περιεκτικότητας καθώς και της εναπομείνουσας αντοχής και δυσκαμψίας συναρτήσει των κύκλων θερμικής κόπωσης και έγινε σύγκριση των πειραματικών αποτελεσμάτων με τις αντίστοιχες προβλέψεις. Από τη σύγκριση αυτή παρατηρούμε ότι τα θεωρητικά μοντέλα που εφαρμόστηκαν που είναι το Μ.P.M (Modulus Predictive Model) και το R.P.M (Residual Properties Model) έδωσαν πολύ καλές προβλέψεις για την μεταβολή των ιδιοτήτων. Σαν γενικό συμπέρασμα από την παρούσα εργασία προκύπτει το γεγονός ότι το φθηνό και ελαφρύ υλικό του ελαιοπυρήνα μπορεί να χρησιμοποιηθεί αποτελεσματικά σαν υλικό ενίσχυσης ρητινών με πολύ καλά αποτελέσματα ενίσχυσης. / The aim of the present master thesis is to investigate the effect of thermal fatigue on the mechanical properties of particulate composites reinforced with olive pit’s powder. The composites materials that have been manufactured were investigated both; experimentally and theoretically. First, we manufactured composites reinforced with olive pits at different volume fractions of the filler particles. From the mechanical characterization of the materials investigated by means of static three-point bending experiments. It was found that the olive pits can reinforce the mechanical properties of composites materials when used as reinforced fillers. Next, the effect of thermal fatigue on the mechanical behaviour of the composites materials was investigated and theoretical predictions for their properties with and without thermal fatigue were made. More precisely, the Μ.P.M (Modulus Predictive Model) and the R.P.M (Residual Properties Model) models have been applied. A fair aggreement between experimental findings and theoretical predictions was found in all cases.

Orientador: Victor Ciro Solano Reynoso / Banca: Keizo Yukimitu / Banca: Raul Fernando Cuevas Rojas / Resumo: O presente trabalho visou a produção e o estudo das propriedades físicas de amostras de resina epóxi transparente dopadas com diferentes concentrações de nanocristais de sulfeto de cádmio (CdS). As técnicas de difração de raios-X, espectroscopia no infravermelho, espectroscopia Raman e calorimetria diferencial de varredura (DSC) foram utilizadas para estudar as propriedades estruturais. Espectroscopias de refletância e de transmitância foram utilizadas para obter a dispersão do índice de refração e do coeficiente de extinção na região do UV-Vis para amostras dopadas com diferentes concentrações de CdS. A técnica do ângulo de Brewster foi também utilizada para determinar o índice de refração das diferentes amostras. Os valores dos índices de refração obtidos através das medidas de refletância e de transmitância na região do UV-Vis e da técnica do ângulo de Brewster foram comparados e os resultados mostraram que a técnica do ângulo de Brewster além de apresentar valores que conferem com a literatura apresentou valores com alta precisão. Foram realizadas medidas de birrefringência opticamente. Foram obtidos resultados da birrefringência fotoinduzida por um fóton para diferentes concentrações de CdS por amostra e para diferentes intensidades da luz de excitação. Os resultados foram quantificados utilizando alguns dos principais modelos teóricos, onde foi observado que a resina epóxi pura apresenta birrefringência fotoinduzida e a adição do CdS contribui para o aumento da birrefringência. / Abstract: The present work sought production and study of the physical properties of samples of transparent epoxy resin doped with different concentrations of structures of cadmium sulfide (CdS) nanocrystals. X-ray diffraction, infrared spectroscopy, Raman spectroscopy e differential scanning calorimetry techniques were used to study their structural properties. Reflectance and transmittance spectroscopy were used to obtain of the refraction index and of the extinction coefficients dispersion in the UVVis region for doped samples with different concentrations of CdS. The Brewster angle technique also was used to determine the refraction index of the different samples. The refraction index values obtained using the reflectance and transmittance measurement in the UV-Vis region and Brewster angle technique were compared and the results showed that the Brewster angle technique besides presents values that check with the literature, presented values with high precision. Measurements of optically induced birefringence were accomplished. Were obtained results of the photo induced birefringence by a photon for different concentrations of CdS for sample and for different intensities of the excitement light. The results were quantified using some of the principal theoretical models, where was observed that the pure epoxy resin presents photo induced birefringence and the addition of the CdS contributes to the increase of the birefringence. / Mestre

Orientador: Newton Luiz Dias Filho / Banca: Devaney Ribeiro do Carmo / Banca: Patrícia Alexandre Antunes / Resumo: Esse trabalho tem como objetivo avaliar as propriedades mecânicas e térmicas de compósitos reforçados com bagaço de cana-de-açúcar. Para a preparação das amostras estudadas o bagaço da cana-de-açúcar foi desmedulado e triturado até atingir um comprimento médio entre 106 e 212 μm. Estas fibras foram tratadas quimicamente com uma solução hidróxido de sódio (NaOH) 10% para, posteriormente, ser adicionado ao epóxi DGEBA/TETA em concentrações de 1, 3, 5, 7,5 e 10% em massa. Foi obtido um aumento de 26,12% no limite de resistência à tração (LRT) do compósito com a adição de 3% de fibras, permanecendo constante em porcentagens superiores. Do mesmo modo, o módulo de elasticidade (E) teve um aumento de 12,5%, e o Limite de Resistência à propagação de trincas (K1C) teve um pequeno decréscimo em relação ao polímero não modificado com a adição de 3% de fibra de cana-de-açúcar (5,6%), permanecendo-se constante em porcentagens superiores. Além disso, os dados obtidos mostram que as propriedades térmicas não foram alteradas com a adição de fibras ao sistema DGEBA/TETA. / Abstract: This work has as objective to evaluate the mechanical and thermal properties of composites reinforced with sugarcane bagasse. For the studied samples preparation the sugarcane bagasse was triturated until being an average lengh between 106 and 212 μm. This fibers were going treated chemically with a solution NaOH 10%, for, afterwards, be added to epoxy DGEBA/TETA in concentrations of 1, 3, 5, 7.5, 10% in mass. An increase of 26,12% in Tensile strength (LRT) with addition of 3% of fibers was obtained, remaining constant to the superior percentages. In the same way, the Modulus of elasticity (E) had an increase of 12,5% and Fracture toughness (K1C) had a small decrease regarding the polymeric not modified (5,6%) with the addition of 3% of sugarcane fiber, remaining constant to the superior percentages. Moreover, the obtained values show that the thermal properties were not changed with the fiber addition in the sistem DGEBA/TETA. / Mestre

La substitution des composés carbonés d'origine fossile par des matières premières renouvelables représente un enjeu majeur et stratégique pour l'environnement, l'économie, et la santé publique. Nous nous sommes particulièrement intéressés au cas des dérivés du phénol, largement utilisés dans le domaine des matériaux synthétiques (résines, plastiques). Des travaux antérieurs ont démontré le potentiel des monomères de flavanols, sous-unités constitutives des chaines polymériques des tanins condensés comme substituts aux phénols issus de la pétrochimie, tels que le bisphénol A, l'objectif du présent travail a été de contribuer au développement d'une voie industrielle d'accès à de tels composés par dépolymérisation des tanins condensés (proanthocyanidines), une ressource végétale abondante mais actuellement peu exploitée pour ce type d'applications. Cette dépolymérisation peut être obtenue par rupture de la liaison interflavanique en milieu acide et piégeage des carbocations formés par un réactif nucléophile. Différentes stratégies et conditions ont été étudiées pour mieux comprendre le rôle de l'acide, du nucléophile, du solvant et l'impact de la température sur la réaction de dépolymérisation. Les stratégies sélectionnées, menées sur un dimère B2 pur servant de modèle et sur un extrait industriel de tanins de pépins de raisins blancs issus de marcs à l'échelle du gramme, ont été comparées en termes de rendement, de cinétique, de stabilité des produits, et de facilité de mise en œuvre et de traitement dans la perspective d'une production à plus grande échelle respectant au mieux les objectifs du développement durable et les contraintes de l'industrialisation. / The substitution of fossil carbon by renewable raw materials is a major strategic challenge for the environment, economy and public health. Our thesis focuses on the utilisation of phenol derivatives, which are widely used in the field of synthetic materials (resins, plastics). Previous studies have demonstrated the potential of plant flavanol monomers as substitutes for petrochemical phenols such as bisphenol A. The objective of this work was to contribute to the development of an industrial access to such compounds by depolymerization of condensed tannins (proanthocyanidins), an abundant plant resource currently untapped for such applications. Depolymerization can be performed by breaking the interflavan bonds in acidic medium and scavenging the released carbocations by a nucleophilic reagent. Various strategies and conditions were studied and compared to better understand the role of the acid, the nucleophile and the solvent and temperature in the depolymerisation reaction. The selected strategies, applied on a pure B2 dimer used as a model and an industrial seed tannins extract from white grape pomace at the gram scale, were compared in terms of performance, kinetics, product stability, ease of implementation and work-up in the context of a larger scale production complying with the objectives of sustainable development and the constraints of industrialization.

Dans le cadre de la caractérisation des combustibles nucléaires irradiés, une résine est utilisée pour enrober des échantillons de matériau combustible. Or la gestion de ces échantillons après usage implique la définition d'un procédé de séparation du matériau combustible de la résine d'enrobage. Cette séparation est en effet rendue nécessaire par la possibilité de dégradation de la résine et de libération de gaz sous l’effet de phénomènes de radiolyse dus aux rayonnements α, β et γ; des combustibles. Un traitement thermique est envisagé pour cette séparation. Les travaux, qui visent à améliorer la connaissance des phénomènes, s'appuient à la fois sur des expérimentations sur systèmes modèles et sur la modélisation des réactions de pyrolyse de la résine et des transferts couplés de matière, de chaleur et de quantité de mouvement. Une des difficultés de l'étude réside dans la nécessité de maîtriser le procédé à différentes échelles : une échelle globale, correspondant aux conditions de traitement visées dans le four, et une échelle locale correspondant aux conditions au voisinage immédiat du matériau combustible. Les essais expérimentaux sont réalisés d’une part en thermo-balance pour l’acquisition de données cinétiques et d’autre part sur un four pilote afin de traiter des quantités plus significatives de résine. Le procédé choisi comporte deux étapes, une première étape de pyrolyse suivie d’une étape d’oxydation du résidu de pyrolyse. Les deux étapes sont susceptibles d’oxyder le combustible lui-même. En effet, la première étape de pyrolyse conduit à la formation d’un mélange gazeux qui peut rendre l’atmosphère localement oxydante. La seconde étape est oxydante par définition. La pyrolyse de la résine produit des gaz incondensables, de la vapeur d’eau, des goudrons et un résidu carboné dont la teneur finale en hydrogène doit être nulle. L’étude du procédé de pyrolyse comporte plusieurs parties. La première partie consiste à étudier la cinétique globale de dégradation de la résine époxy et à déterminer la cinétique de dégagement des différents gaz. Pour prendre en compte la présence du combustible dans le milieu de traitement, des expériences de traitement d’un mélange époxy-UO2 en thermo-balance ont été réalisées. Les résultats montrent l’absence d’un effet significatif de la présence du combustible. La deuxième partie est l’intégration des résultats expérimentaux obtenus dans le modèle. La modélisation du four est réalisée dans l’environnement COMSOL Multiphysics®. Les résultats montrent un bon accord avec les mesures expérimentales. Sur la base de cette modélisation, une amélioration du four d’essai a été proposée. A la fin de l’étape de pyrolyse, la phase solide résiduelle contient toujours de l’hydrogène. Pour minimiser cette quantité, l’oxydation du résidu de pyrolyse est une étape nécessaire. Deux types de procédés ont été proposés à savoir l’oxydation sous une atmosphère contrôlée en oxygène et la gazéification sous dioxyde de carbone qui permettent l’élimination du résidu de pyrolyse en laissant intègre le combustible uranium dans des conditions bien définies. / In order to characterize nuclear fuels, samples are currently embedded in an epoxy polymer resin. In storage conditions, the presence of organic products in contact with highly radioactive material generates gas due to a radiolysis phenomenon. Samples management imposes the definition of a fuel and resin separation process. This work aims at developing a tool for the optimal design and control of a suitable heat treatment process. This development is based on experiments and on the modeling of the resin pyrolysis reactions coupled to mass, heat and momentum transfers. One of the difficulties of the study lies to the needed process control on various scales: i) on a global scale to represent the treatment conditions and ii) on a local scale to represent the conditions close to fuel material. This study uses a combined modeling - simulation approach with experiments carried out with the help of a thermo-balance for kinetic data acquisition, on the one hand and in an experimental oven, on the other hand. The process will be performed in two stages, resin pyrolysis and residue (Char) oxidation. Nuclear fuel can be oxidized during both stages. Indeed, the pyrolysis degrades the resin and generated pyrolysis gases, which produce an oxidizing atmosphere. Oxidation of pyrolysis residue can modify the structure of spent fuel and liberate fission gases. The resin pyrolysis produced incondensable gases, steam, tar and char. The final hydrogen content in the char has to be as low as possible and close to zero to be sure that the radiolysis phenomenon will never occur during of nuclear fuel storage. The process development has been carried out in stages. The first step is to investigate the overall kinetics of epoxy degradation and the determination of the generated gas kinetics. The influence of the presence of nuclear fuel is investigated with epoxy-UO2 mixture. The results showed no significant effect of the nuclear fuel presence. The second part is the coupling of kinetic model to the partial differential equations (mass, energy and momentum balance) to obtain a representative model of the oven in terms of temperature and chemical species composition. The Modeling of the oven is carried out using COMSOL Multiphysics® software. The results showed a good agreement with experimental measurements. After pyrolysis, char still contains significant amount of hydrogen. To minimize this quantity, the oxidation of the char is a necessary step. Two treatment types are proposed: An oxidation under a controlled oxygen atmosphere and carbon dioxide gasification. These methods are efficient to eliminate the residual of hydrogen content while keeping the fuel integrity.

Orientador: Prof. Dr. Gerson Luiz Mantovani / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016. / Neste trabalho foram estudados processos de funcionalização de resinas epoxídicas. O processo de funcionalização foi realizado por meio da incorporação controlada de compósitos de polianilina (PANI) reforçada com negro de fumo (PANI/NF) na matriz epoxídica. A produção dos compósitos de PANI/NF foi realizada por meio da polimerização da anilina na presença do negro de fumo resultando na polimerização preferencial da anilina na superfície do negro de fumo. A formação da estrutura do tipo caroço-casca (core-shell) foi evidenciada pelas diferenças observadas na morfologia do material resultante da polimerização da anilina na presença e na ausência do negro de fumo. Na ausência de negro de fumo foi observada uma estrutura constituída de fibras curtas com diâmetro da ordem de 100 nm e na presença de negro de fumo foi observada uma morfologia essencialmente granular. As caracterizações da PANI, do NF, do compósito PANI/NF e da resina epoxídica foram realizadas por meio de técnicas de espectroscopia de absorção na região do ultravioleta e visível (UV-VIS), espectroscopia de infra vermelho por transformada de Fourier (FTIR), espectroscopia Raman, calorimetria exploratória diferencial (DSC) e microscopia eletrônica de varredura (MEV). A incorporação do compósito de PANI/NF à resina epoxídica ocorreu por mistura mecânica. Os resultados de espectroscopia Raman que o NF apresentou uma razão entre a intensidade das bandas D e G (ID/IG) igual a 8,7, característico de um sistema com uma alta quantidade de defeitos e de baixa cristalinidade. Os resultados de DSC mostraram que após esta mistura da resina epoxídica com PANI/NF o processo de cura da resina epoxídica não foi afetado de forma significativa. A capacidade de proteção contra a corrosão do revestimento foi avaliada por meio de ensaios eletroquímicos de corrosão, sendo, monitoramento de potencial de corrosão em circuito aberto e espectroscopia de impedância eletroquímica. Os resultados dos ensaios eletroquímicos mostraram um aumento na proteção contra a corrosão do revestimento epoxídico devido às propriedades anticorrosivas do compósito PANI/NF. / In this work it was studied the functionalization of epoxy resin. The functionalization process will be carried out by the modification of the epoxy resin matrix by adding polyaniline / carbon black composites (PANI/NF). The production of composite PANI / NF was performed by polymerizing aniline in the presence of carbon black resulting in preferential polymerization of aniline on the carbon black surface. The formation of core-shell type structure (core-shell) was evidenced by the differences in the morphology of the material resulting from the polymerization of aniline in the presence and absence of carbon black. In the absence of black smoke was observed structure composed of short fibers having a diameter of approximately 100 nm in the presence of carbon black essentially a granular morphology was observed. The characterization of the PANI, NF, composite PANI / NF and epoxy resin were carried out using the absorption spectroscopy techniques in the ultraviolet and visible region (UV-VIS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The incorporation of the composite PANI / NF to epoxy resin occurred by mechanical mixing. The results of differential scanning calorimetry (DSC) showed that after this mixture of epoxy resin with PANI / NF, the epoxy resin curing process was not affected significantly. The ability to protect against corrosion coating was evaluated by, electrochemical tests of potential corrosion monitoring in open circuit and electrochemical impedance spectroscopy. The results of the electrochemical tests showed an increase in protection against corrosion the epoxy coating due the anticorrosive properties of PANI / NF composite.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-03-19Bitstream added on 2014-06-13T19:32:44Z : No. of bitstreams: 1 barbosa_fm_me_ilha.pdf: 653354 bytes, checksum: 02df88d00b7fb4617013dfd71a48398b (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Esse trabalho tem como objetivo avaliar as propriedades mecânicas e térmicas de compósitos reforçados com bagaço de cana-de-açúcar. Para a preparação das amostras estudadas o bagaço da cana-de-açúcar foi desmedulado e triturado até atingir um comprimento médio entre 106 e 212 μm. Estas fibras foram tratadas quimicamente com uma solução hidróxido de sódio (NaOH) 10% para, posteriormente, ser adicionado ao epóxi DGEBA/TETA em concentrações de 1, 3, 5, 7,5 e 10% em massa. Foi obtido um aumento de 26,12% no limite de resistência à tração (LRT) do compósito com a adição de 3% de fibras, permanecendo constante em porcentagens superiores. Do mesmo modo, o módulo de elasticidade (E) teve um aumento de 12,5%, e o Limite de Resistência à propagação de trincas (K1C) teve um pequeno decréscimo em relação ao polímero não modificado com a adição de 3% de fibra de cana-de-açúcar (5,6%), permanecendo-se constante em porcentagens superiores. Além disso, os dados obtidos mostram que as propriedades térmicas não foram alteradas com a adição de fibras ao sistema DGEBA/TETA. / This work has as objective to evaluate the mechanical and thermal properties of composites reinforced with sugarcane bagasse. For the studied samples preparation the sugarcane bagasse was triturated until being an average lengh between 106 and 212 μm. This fibers were going treated chemically with a solution NaOH 10%, for, afterwards, be added to epoxy DGEBA/TETA in concentrations of 1, 3, 5, 7.5, 10% in mass. An increase of 26,12% in Tensile strength (LRT) with addition of 3% of fibers was obtained, remaining constant to the superior percentages. In the same way, the Modulus of elasticity (E) had an increase of 12,5% and Fracture toughness (K1C) had a small decrease regarding the polymeric not modified (5,6%) with the addition of 3% of sugarcane fiber, remaining constant to the superior percentages. Moreover, the obtained values show that the thermal properties were not changed with the fiber addition in the sistem DGEBA/TETA.

Polymeric insulating materials are being re-evaluated in the context of the re-emergence of HVDC and its advantages in bulk power transfer over long distances. This has been met with new sets of requirement such as; the use of polymeric insulation, compaction of HV equipment (e.g. HV cables), and innovations in converter technology. This equipment requires high power rating and hence will be exposed to high electric stresses. One of the properties of polymeric DC insulation is its ability to retain injected charges at high DC fields leading to local field modification and subsequent breakdown of the insulation through electrical treeing. Electrical treeing is one of the important failure mechanisms of solid polymeric insulations resulting from high voltage stresses and a precursor to failure of electrical equipment. Hence, the performance and reliability of polymeric insulation designs will be affected by electrical treeing. Literature shows that electrical trees initiate easily with switching voltages such as impulses, voltage surges and reversal of power flow direction. Innovations in converter technology employs fast switching devices such as insulated gated bipolar transistors (IGBTs) which generates substantial amount of harmonics and may also impact insulation systems reliability. This research investigates the reliability of epoxy resin (LH/HY 5052) for suitability in HVDC applications due to its excellent properties as jointing compound in medium and high voltage cables systems. The development of test facilities for short term breakdown strength, space charge measurement and electrical treeing experiment have allowed short term breakdown strength on homogeneous layers of thin epoxy-epoxy samples and long term breakdown through electrical treeing under DC, AC and AC superimposed on DC to be investigated so that an understanding of the link between space charge, material strength and life times can be clarified. The results on short term breakdown showed the layered samples have 6% reduction in strength compared to un-layered samples. For long term treeing test, 100% of the samples stressed with negative DC did not fail while 67% of the sample stressed with positive DC failed with average lifetime of 250 minutes. Samples stressed under AC showed forward and reverse directions of tree growth with average lifetime of 143 minutes from 70% failed samples. For AC superimposed on ±DC all samples failed with average lifetimes of 54 and 78 minutes for positive and negative bias tests, respectively. It is concluded that, the differences in lifetime obtained under positive and negative pure DC tests and that of the positive and negative DC bias tests are associated with space charge causing field relief under negative DC and negative bias tests. The huge reduction in lifetimes under AC superimposed on DC as ripples tests highlights the potential threat of power quality issues on the reliability of DC systems. Electrical tree growth from the ground planer electrode (reverse tree) observed under AC test was associated with relatively low voltage under AC test compared with the other tests see Table 8-1 for test voltages employed.