Compósitos desenvolvidos a partir da incorporação de rejeitos industriais além de serem mais uma opção disponível às mais diversas aplicações, podem promover a redução de passivos ambientais gerados durante anos. Visando atender à essas questões, foram desenvolvidos compósitos com matriz de resina epóxi carregados com rejeito de scheelita nas proporções de 1%, 5%, 10%, 20 % e 30%. Para tanto, o rejeito de scheelita foi, inicialmente, caracterizado por meio de FRX, DRX e MEV. Já a resina epóxi foi analisada por meio de FTIR antes e após a cura. Duas condições de cura foram adotadas para a confecção dos corpos de prova, uma realizada somente a temperatura ambiente e outra executada à temperatura ambiente com uma etapa de pós cura térmica realizada a 80°C por 5 horas. Os corpos de prova foram moldados por casting em molde de silicone e as proporções foram calculadas em volume. A massa específica dos compósitos foi determinada. Para caracterizar o desempenho mecânico das composições foram realizados ensaios de tração e ensaios de dureza os quais evidenciaram que as frações de carga mineral influenciam positivamente o módulo de elasticidade e a dureza e afetam negativamente a resistência à tração. Os parâmetros Ra, Rq e Rz foram medidos e considerados na caracterização do acabamento superficial. Ensaios de deslizamento com a configuração pino contra disco foram realizados para caracterizar o desempenho tribológico dos compósitos que geraram respostas de coeficiente de atrito e profundidade da trilha do desgaste. Os corpos de prova em forma de disco foram confeccionados com os diferentes compósitos e como pinos foram utilizadas esferas de aço AISI 52100. O compósito com 10% de carga apresentou o melhor desempenho tribológico com coeficiente de atrito variando entre 0,1 e 0,4 e profundidade da trilha do desgaste entre 25 e 50 µm. As imagens de MEV realizadas nas superfícies de ruptura dos corpos de prova de tração e nas superfícies desgastas dos discos utilizados nos ensaios pino contra disco revelaram desprendimento de material e partículas soltas sugerindo baixa adesão interfacial carga/matriz. De modo geral, as respostas obtidas estão de acordo com o que expressa a literatura. / Composites that incorporate industrial waste are an option for a wide range of applications and can also reduce the environmental passive generated over years. To address these issues, composites of epoxy resin loaded Scheelite Tailings in proportions of 1%, 5%, 10%, 20% and 30% were developed. For this, the Scheelite Tailings was characterized by XRF, XRD and SEM. The epoxy resin was analyzed by FTIR before and after curing. Two curing conditions were used for the preparation of the test specimens, at ambient temperature and the other at room temperature with a post-curing step at 80 ° C for 5 hours. The specimens were molded by casting in silicone mold and the proportions were calculated by volume. The specific mass was determined. The mechanical performance of the compositions was characterized by tensile and hardness tests which, the results showed that the mineral filler fractions generate positive effect on the Young\'s modulus and hardness and negative effect on the tensile strength. The parameters Ra, Rq and Rz were measured and considered as characterization of the surface finishing. Sliding tests with the pin on disk configuration were performed to characterize the tribological performance of the composites that generated friction coefficient responses and depth of the wear track. The disk specimens were made with the different compositions and the pins were AISI 52100 steel balls. The composite with 10% of scheelite tailings presented the best tribological performance with coefficient of friction varying between 0.1 and 0.4 and depth of the wear track between 25 and 50 50 µm. The SEM images performed on the tensile test specimen rupture surfaces and on the wear surfaces of the disks used in the pin to disk tests indicate release of material and loose particles suggesting low interfacial adhesion of mineral filler/matrix. In general, the answers obtained are in agreement with what is expressed in the literature.

The focus of this study is mono-layer polymer light emitting diode (PLED). The emitting layer is poly-p-phenylenebenzobisoxazole (PBO). PBO is a fully conjugated heterocyclic aromatic rigid-rod polymer. Anode is indium-tin-oxide (ITO). Cathode is aluminum (Al). We used UV epoxy resin to package PLED devices, then measured current-voltage response, electroluminescence (EL) emission, and device lifetime. We demonstrate that the packaged mono-layer PBO LED reduced its demise from water and oxygen. Device lifetime increased from 1 hour to several hundred hours. At a larger bias voltage or current, emission intensity and device efficiency became higher. But decay rate increased leading to shortened device lifetime. Device temperature appeared linearly with current density. A red shift of the EL emission was observed. The £fmax. of emission spectra moved from 534 nm (initial) to 582 nm (after 100 hrs). After thermal annealing at 120¢J for ten hours, threshold voltage increased from 5 V to 12 V, current density decreased to several 10 mA/cm2, luminous intensity improved several ten times to 10-2 cd/m2, emission color changed from yellow-green to orange, luminous efficiency improved from 10-7 to 10-4 cd/A, but device lifetime declined to less than 20 hrs.

Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rod like backbone entailing excellent mechanical properties, thermo -oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A CNT of multi-wall carbon nanotube (MWNT) was dissolved in a Lewis acid solution of PBO for dispersion, and then spun for thin film. MWNT concentration in the films was from zero up to 5 wt. %. Compared to that of pure PBO film, all PBO/MWNT composite films retained same but enhanced UV-Vis absorption peaks, according to MWNT concentration, showing that PBO and MWNT did not have overlapping electron orbitals affecting their energy gaps. The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) emission. All PL spectra had maximum intensity at 540 nm indicative of yellow-green light emission. The composite films were fabricated as light emitting diodes using indium-tin-oxide/glass as substrate and anode, as well as vacuum evaporated Al as cathode for respectively hole and electron injectors. In these light emitting devices, MWNT doped PBO would decrease threshold voltage for about 2 V. Up to 0.1 wt. % of MWNT, the device emission current was increased two orders of magnitude than those of the devices without MWNT. Further increase of MWNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect from aggregations of MWNTs. UV epoxy resin was applied to package the mono-layer and bilayer PBO light emitting devices. The UV epoxy resin had some gas release during encapsulation. The devices were packaged with vacuum and without vacuum encapsulation. It was demonstrated that the device encapsulation reduced its demise from water and oxygen. The vacuum encapsulation could remove gaseous volatile of the device to inhibit oxygen and moisture to prolong device lifetime. The main degradation of light emitting device was the oxidization of cathode. The interactions between nitrogen of PBO and H2O caused the formation of hydrogen bonding at room temperature. Oxygen and moisture diffused into PBO polymer and were suspected to form mid-gap state for the polymer. The mid energy band disappeared upon heat treatment before encapsulation. A device under a higher bias voltage was found to have a shorter lifetime, but a larger EL emission intensity. The EL emission intensity was not a constant under a constant current bias. The vacuum encapsulated device had two or twenty times lifetime than, respectively, the device encapsulation without vacuum evacuation or in ambient conditions. The sandwich structure of ITO/PBO/Al had no observable photovoltaic effect due to insufficient exciton separation into electrons and holes. Poly(2,3-dihydro thieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS), a hole transferring medium, was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for the PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and the maximum short circuit current (Isc) were achieved with a LiF thickness of 1-2 nm due to possible electric dipole effect leading to an increase of Voc from 0.7 V to 0.92 V and of Isc from about 0.1

Polymer-clay nanocomposites have received a lot of attention because of outstanding improvements in properties when compared with neat polymeric materials. The aim of this study was to prepare epoxy-clay nanocomposites by mixing organically modified montmorillonite with an epoxy resin and to investigate the effects of clay content on the mechanical, thermal and flammability properties of the resultant nanocomposites. The production of the epoxy-clay nanocomposites was accomplished by in-situ polymerization. In the nanocomposite synthesis, organically modified clay content was varied from 1 wt.% to 9 wt.%. Araldite LY556 epoxy resin, Aradur 918 anhydride hardener, and DY070 imidazole type accelerator were used in the epoxy system. Closite 30B, an organoclay modified with methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium chloride (MT2EtOH), was used as the clay material. X-ray diffraction results showed that d-spacing between the platelets of organoclay increased from 1.80 nm to 4.4 nm. The microstructures of nanocomposites were investigated by scanning electron microscopy (SEM). The SEM micrographs indicated that at 1 wt.% clay loading, no clay aggregates were observed. On the other hand, beyond 1 wt.% clay loading, formation of clay agglomerations was observed. Tensile strength and tensile strain values of nanocomposites decreased with clay loading. The tensile strength value of neat epoxy resin decreased from 55 MPa to 29 MPa with 9 % clay loading. On the other hand, Young&amp / #8217 / s modulus increased with clay content and a maximum value was obtained at 5 wt. % clay loading. At 9 % clay loading, Young&amp / #8217 / s modulus value was 26 % higher than that of the neat epoxy resin. Impact strength property had a minimum value at 7 wt. % clay content. Flexural strength and flexural strain at break property behaved in a similar trend. They had a minimum value at 5 % clay loading. At this clay loading, flexural strength value became approximately 43 % lower compared to the flexural strength of the neat epoxy resin. On the other hand, at 9 wt.% clay loading flexural modulus value increased approximately 48 % compared to the pure epoxy resin. Up to 7 wt.% clay ratio, initial decomposition temperature of epoxy resin was slightly improved. Also, according to TGA results, amount of char formation increased with clay loading. DSC results indicate that Tg of the cured nanocomposite resins decreased from 147 oC to 129 oC with 9 wt. % clay loading. The flammability of neat epoxy resin was not significantly affected with Cloisite 30B addition.

Carbon nanotubes (CNTs) are a relatively new allotrope of carbon that possess very unique and exciting physical characteristics. However, much is still unknown regarding their physical structure and chemical reactivity. The focus of this dissertation is to utilize the chemical modification of these filamentous carbon structures as a probe to investigate the structure and reactivity of carbon nanotubes. Also discussed is the ability of CNTs, once chemically modified, to interact with specific polymer matrices and how the addition of modified and unmodified CNTs affects the physical properties of these matrices.

Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with organoclays have been investigated. The main objective of this study was to determine which combination of components led to the greatest enhancement in properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated nanocomposites are known to exhibit great improvements in mechanical properties [1]. The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM. The epoxy resin was cured with three different hardeners, these included: the high functionality amine hardener, TETA, and two anhydride hardeners, accelerated MTHPA and pure HHPA. The three organoclays used, contained alkylammonium cations and were also compared to the unmodified clay. Morphology was investigated by XRD and TEM, and the flexural properties of the resulting nanocomposites were studied. The effect that the addition of an organoclay has on the cure of the epoxy resin was investigated using MDSC. Both the temperatures required to cure the resin with, and without, the clay, and any changes in the total heat flow that occurred were studied. The Tg++ of the cured nanocomposites was also measured using MDSC. The heat flow results indicated that the clays added to the epoxy resins act as a physical barrier, which prevents the resin from reaching full cure. In the higher functional resin, the addition of clay resulted in a significant decrease in the total heat flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there should be a reduction in the amount of cross-linking. The lower cross-link density led to a significantly lower Tg and the mechanical properties were also poorer. The reactivity of the hardener towards the resin was found to have the greatest impact on the cured nanocomposite morphology. Intragallery polymerisation occurring at a faster rate than the extragallery polymerisation causes exfoliation. In order to achieve a balance that favours intragallery polymerisation, it was found that the curing reaction was required to be catalysed by the alkylammonium cation of the organoclay, and not catalysed by other means. The DGEBA cured with HHPA provided the largest layer expansion in the clay structure due to the alkylammonium cation catalysing the anhydride ring-opening reaction. The effect was not seen with TGDDM due to the tertiary amine in its structure. The accelerator within the MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily without additional catalysis.

Made available in DSpace on 2016-08-03T16:31:16Z (GMT). No. of bitstreams: 1 Miller Zaroni Santoro.pdf: 2303143 bytes, checksum: c5e5ddd496f8c0c48e1af99dfe38af5b (MD5) Previous issue date: 2011-04-29 / The aim of this study was to compare the forces of deflection in vitro between aesthetic and wire NiTi wires, to check the maximum force and plateau region and determine its correlation with the diameter of the wire with and without coating. Ten trials were conducted in seven brands of bows pre-skirted, six-wire aesthetic (InVu (I), Optis (O), Flexy Super Elastic Esthetic (FSEE), Orthocosmetic Elastinol (OE), Niticosmetic (N), and Pro Form Coated Nitanium (PFCN)) and a superelastic NiTi wire (Nitinol Super Elastic (NSE), applying The test is three-point bending, associated with universal machine EMIC. We developed a device with ceramic brackets (Transcend), whose strings were arrested for elastic modular, and obtained the values of the force deflection at 3.0, 2.0 and 1.0 mm. The diameter of the wires with and without coating were measured using digital especímetro Micromaster. The analysis of variance with a criterion (p <0.05) showed significant difference between the wires and post-hoc Tukey test determined that the force at 3mm deflection for wire O<OE=PFCE<FSEE=NSE<I. The paired t-test compared the strength of deflection (2-1mm) in the plateau region and showed that the wires O, FSEE and N showed constant forces. The wire N showed the largest diameter among the samples, while NSE wires and O, minors. The Pearson correlation coefficient showed that there was a correlation between the diameter of the wire and the force of deflection. It can be concluded that there are differences between the forces produced by the wires and aesthetic that force is directly proportional to the diameter of the uncoated wire for all peaks, ie the larger the diameter, the greater the force produced. / O objetivo do presente estudo consistiu em comparar as forças de deflexão in vitro entre fios estéticos e fio NiTi, para verificar a força máxima e da região platô e determinar sua correlação com o diâmetro do fio com e sem revestimento. Foram realizados dez ensaios de sete marcas comerciais de arcos précontornados, sendo seis fios estéticos (Invu (I), Optis (O), Flexy Super Elastic Esthetic (FSEE), Niticosmetic (N), Orthocosmetic Elastinol (OE) e Pro Form Coated Nitanium (PFCN)) e um fio NiTi superelástico (Nitinol Super Elastic (NSE)), aplicando-se o teste de curvatura de três pontos, associado a máquina de ensaios universal EMIC. Desenvolveu-se um dispositivo com braquetes cerâmicos (Transcend), cujos fios foram presos por elásticos modulares, sendo obtidos os valores da força de deflexão em 3,0, 2,0 e 1,0mm. O diâmetro dos fios com e sem revestimento foram mensurados com o especímetro digital Micromaster. A análise de variância a um critério (p<0,05) mostrou diferença significante entre os fios e o teste post-hoc de Tukey determinou que a força de deflexão em 3mm para o O<OE=PFCE<FSEE=NSE<I. O teste t-pareado comparou a força de deflexão (2-1mm) na região platô e mostrou que os fios O, FSEE e N apresentaram forças constantes. O fio da N apresentou o maior diâmetro entre as amostras, enquanto que os fios NSE e O, os menores. O Coeficiente de Correlação de Pearson mostrou que houve correlação entre o diâmetro do fio e a força de deflexão. Pode se concluir que há diferenças entre as forças produzidas pelos fios estéticos e que a força é diretamente proporcional ao seu diâmetro do fio com e sem revestimento para todas as deflexões, ou seja, quanto maior o diâmetro, maior a força produzida.

As resinas termorrígidas são uma classe de polímeros que devido à reação de reticulação deveriam apresentar uma única cadeia molecular de peso infinito, no entanto, questionamentos sugerem que a formação da rede tridimensional é não-homogênea. Atualmente, devido aos avanços obtidos pela nanotecnologia, torna-se possível uma abordagem diferenciada na modificação química de polímeros como a resina epoxídica. Neste trabalho, foram preparados nanocompósitos adicionando diferentes teores do oligômero poliédrico de silsesquioxano (POSS) n-fenilaminopropil na resina epoxídica. Foi substituindo 1, 5 e 10 por cento em massa (% m.) do agente de reticulação trietilenotetramina (TETA) por POSS. Esta modificação foi realizada com o objetivo de promover maior concentração de interligações nas interfaces das regiões nodulares, descritas como imperfeições ou descontinuidades que ocorrem pela cura não-homogênea da resina. Através da morfologia e da análise do teor de gel, foi evidenciada boa dispersão e melhoria na homogeneidade da rede tridimensional da resina acima de 5 % m. de POSS e aumento da fração gel nos nanocompósitos comparados com a resina epoxídica pura. Na realização de análises de difração de raio-x (DRX) foi visto que a adição do POSS aumentou a distância média entre as cadeias da resina. Foi realizada análise dinâmico-mecânica (DMA) no modo não-isotérmico e por varredura de frequência no modo isotérmico. Pelo modo não-isotérmico os resultados demonstraram que o POSS deslocou a Tg para temperaturas maiores e não alterou significativamente a densidade de ligações cruzadas da resina epoxídica. O modo isotérmico foi utilizado para a determinação de parâmetros das equações de Williams-Landel-Ferry (WLF) e Vogel-Fulcher-Tammann (VFT). Foi calculada a distribuição dos espectros de relaxação H(t) e retardação L(t) molecular através dos módulos de armazenamento e perda obtidos pelo modo isotérmico no DMA. Os parâmetros WLF e VFT demonstraram que a incorporação do POSS ao mesmo tempo em que aumentou a Tg, reduziu a energia de ativação de movimentação segmentar e tornou a resina epoxídica mais forte estruturalmente. A redução da energia de ativação foi associada com a redução das forças de interação intermolecular, enquanto que a redução da fragilidade foi associada ao fato do POSS ser capaz de interligar as interfaces de regiões nodulares. Os espectros H(t) e L(t) mostraram que o pico de relaxação associado aos nódulos formados no processo de reticulação desapareceu. A determinação da capacidade calorífica (Cp) e do excesso de entropia (Sex) através de análises de calorimetria exploratória diferencial modulada (MDSC) demonstrou que o POSS é capaz de minimizar as flutuações de calor ao longo da microestrutura da resina epoxídica. A minimização das flutuações térmicas e a alteração dos tempos de relaxação demonstram que a adição do POSS é eficiente em termos de minimização de imperfeições na microestrutura da resina epoxídica. / The thermosetting resins are a class of polymers that due to the crosslinking reaction should present a single chain with infinite molecular weight; however, questions suggest that the formation of three-dimensional network is non-homogeneous. Today, due to advancements in nanotechnology, became possible a differentiated approach in the chemical modification of polymers such as epoxy resin. In this work, nanocomposites with different contents of the polyhedral oligomeric silsesquioxane (POSS) n-phenylaminopropyl in epoxy resin were prepared. It was substituted 1, 5 and 10 weight percent (wt%) of the crosslinking agent, triethylenetetramine (TETA), for POSS. This modification was performed in order to promote greater concentration of interconnections at the interfaces of the regions described as nodular imperfections or discontinuities that arise due to inhomogeneous cure of the resin. Through the morphology and the gel content analysis was observed good dispersion and improvements in the uniformity of three-dimensional network of the resin up till 5 wt% of the POSS and increase in the gel fraction of the nanocomposites compared with pure epoxy resin. X-ray diffraction (XRD) showed that the POSS promoted an increase in distance between chains of the resin. Dynamic-mechanical analysis (DMA) was performed in non-isothermal mode and a frequency sweep in the isothermal mode. By non-isothermal mode the results showed that the POSS shifted the Tg to higher temperatures and does not modify the crosslink density. The isothermal mode was used to determine the parameter of the Williams-Landel-Ferry (WLF) and Vogel-Fulcher-Tammann (VFT) equations. The distribution of the relaxation H(t) and retardation L(t) spectra was calculated through the storage (E') and loss (E'') modulus obtained by the DMA isothermal mode. The WLF and VFT parameters showed that the incorporation of POSS at the same time increased the Tg reduced the activation energy of segmental motion and made the epoxy resin structurally stronger. The reduction in the activation energy was associated with reduced intermolecular forces whereas the decrease in the structural fragility is associated with the fact that the POSS be able to interconnect the interfaces of the nodular regions. The H(t) and L(t) spectra showed that the nodules formed in the crosslinking process disappeared. The determination of the heat capacity (Cp) and excess entropy (Sex), analyzed by modulated differential scanning calorimetry (MDSC), showed that POSS is capable of minimizing fluctuations of heat along the microstructure of the epoxy resin. The reduction of thermal fluctuations and change in the relaxation times shows that the POSS addition is efficient to minimize imperfections in the microstructure of the epoxy resin.

Nas extremidades dos dutos flexíveis utilizados na indústria petroleira offshore são instalados os end fittings, ou conectores. Uma parte fundamental deste componente é o sistema de ancoragem, que consiste nos arames de aço da armadura de tração embebidos em resina epóxi, onde seu propósito é transmitir os esforços que provêm do duto. Este estudo tem como objetivo apresentar uma avaliação de três diferentes resinas epóxi (Huntsman: SW404/HY404, AW4804/HW4804 e XAW1395/HY950) comparando as propriedades mecânicas e a influência do ambiente de serviço, a fim de definir qual melhor se adequa para este fim. As propriedades mecânicas das resinas epóxi foram determinadas através de ensaios de compressão, tração, cisalhamento, pullout e medições de dureza. Os denominados ensaios de pullout representam um modelo simplificado do sistema de ancoragem e possibilitam o estudo da interface entre a resina e o aço da armadura de tração. Para avaliar o efeito da exposição do polímero às condições ambientais de serviço, amostras foram envelhecidas numa solução de água marinha na temperatura constante de 60°C, durante um período de 6 meses. Após este período, realizaram-se ensaios de compressão, cisalhamento e pullout, cujos resultados foram comparados com os obtidos de amostras sem nenhum período de exposição. A influência das elevadas temperaturas sobre a propriedade de adesão nas diferentes resinas foi avaliada mediante ensaios de pullout realizados à temperatura de 100°C. Além disto, foi realizada uma análise térmica através de ensaios de TGA e DMTA. Por fim, às propriedades determinadas nos diferentes ensaios e medições lhes foram atribuídas um peso quantitativo de acordo com sua importância dentro do sistema de ancoragem. Os valores das propriedades e seus pesos foram introduzidos a uma matriz de análise de multicritérios, que permitiu selecionar a resina epóxi com a melhor combinação de propriedades para ser aplicada em end fittings. Finalmente, é proposta a determinação de alguns parâmetros adicionais das resinas epóxi para complementar o estudo realizado / End fittings are components that are installed at the ends of flexible pipes used in the offshore oil industry. A fundamental part of this component is the anchoring system, which consists of the steel wires of the tensile armour embedded in epoxy resin, which its purpose is to transmit the loads that come from the pipe. This study aims to present an evaluation of three different epoxy resins (Huntsman: SW404/HY404, AW4804/HW4804 e XAW1395/HY950), comparing the mechanical properties and studying the influence of the service environment, in order to define which material is best suited for this application. The mechanical properties of the epoxy resins were determined by tests such as compression, tensile, shear and pullout tests and hardness measurements. The pullout tests represent a simplified model of the anchoring system and they allow the study of the interface between the resin and the steel of the tensile armour. To evaluate the effect of the exposition of the polymer material to environmental conditions found in service, some samples were immersed in a bath of sea water at a constant temperature of 60°C during a period of 6 months. After this period, compression, shear and pullout tests were performed and the results were compared with those obtained from samples without degradation. The influence of the high temperatures on the adhesion property of the different epoxy resins was evaluated with pullout tests performed at a temperature of 100°C. Furthermore, a thermal analysis was realized through TGA and DMTA tests. Finally, to the properties determined in the different tests and measurements were given a quantitative weight according to their importance within the anchoring system. The values of the properties and their weights were introduced into a matrix of multicriterial analysis that allowed selecting the epoxy resin with the best combination of properties to be applied in end fittings. Finally, it was proposed the determination of other epoxy resins parameters to complement this study.

Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-08-30Bitstream added on 2014-06-13T18:29:01Z : No. of bitstreams: 1 rangel_sa_me_ilha.pdf: 1557624 bytes, checksum: 38398c09b8ff17af075a211027a27833 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Polímeros epoxídicos são um dos mais importantes tipos de polímeros termorrígidos, extensivamente usados como adesivos e estruturas. Em reações epoxídicas são convertidos em um sistema termorrígido pela ação de agentes de cura. Tais reações químicas provocam uma mudança no estado físico do material, partindo de um líquido viscoso para um gel e se transformando em um material vitrificado. Os termorrígidos apresentam excelentes propriedades, tais como: alta tensão de ruptura e módulo de Young, fácil processamento, resistência térmica e química, e estabilidade dimensional. Entretanto, são quebradiços e possuem baixa resistência a propagação de trincas. Para superar estes inconvenientes, muitos tipos de compósitos de polímero com reforço foram desenvolvidos, em que as resinas epoxídicas são reforçadas com agentes modificadores, tais como enchimentos, oligômeros poliédricos de silsesquioxanos, dendrímeros, etc. Oligômeros poliédricos de silsesquioxanos (POSS), (RSiO1.5)n com n = 4, 6, 8, 10..., são nanoplataformas organo-funcionalizadas com 1 a 8 grupos reativos ou não reativos (R) ligados aos oito vértices possíveis do silsesquioxano cúbico. POSS octaédrico (n = 8) são os membros mais importantes desta família. No POSS, o núcleo cúbico de silicato é uma partícula rígida com 0,53 nm de diâmetro e um raio esférico de 1-3 nm, incluindo unidades orgânicas periféricas. Neste trabalho, um oligômero poliédrico de silsesquioxano contendo oito grupos epoxídicos por molécula (OG) foi incorporado ao sistema epoxídica DGEBA/DETA, como objetivo de avaliar a influência de um modificador reativo suas propriedades mecânicas e térmicas. Por meio de ensaios mecânicos foi observado um decréscimo de 30-50% na resistência à fratura (K1C)... / Epoxy resins are one of the most important kind of thermosetting polymers, extensively used for adhesives and structural applications. On cure, linear epoxy resins are undergoes in a thermoset system for the action of cure agents. Such chemical reactions cause a change into the physical state, from a viscous liquid to a gel and eventually to a vitrified material. They show various desirable properties such as high tensile strength and modulus, easy processing, good thermal and chemical resistance and dimensional stability, but they are brittle and have poor resistance to crack propagation. To overcome these drawbacks, many types of polymer-filler composites have been developed, in which the epoxy resins are reinforced with modifying agents, such as fillers, polyhedral oligosilsesquioxanes, dendrimers, etc. Polyhedral oligomeric silsesquioxanes (POSS), (RSiO1.5)n with n = 4, 6, 8, 10 ...., are organofunctional nanoplatforms with 1 to 8 reactive or nonreactive groups (R) connected to the eight possible vertexes of cubic silsesquioxanes. POSS Octahedral (n = 8) are the most important members of this family. In the POSS, the cubic core silica is a hard particle rigid with 0.53 nm diameter and a spherical radius of 1-3 nm including peripheral organic units. In this work, a polyhedral oligomeric silsesquioxanes containing eight epoxy groups per molecule (OG) was incorporated to an epoxy system of DGEBA/DETA thermosetting polymers in order to investigate the influence of a reactive modifier over the their mechanical and thermal properties. Through the mechanical tests an decrease of about 30-50% was observed in the fracture toughness (K1C) without or with a very soft decreasing in the module of Young (E)... (Complete abstract, click electronic address below)