In the present study the effects of addition of organically functionalized boehmite nano-particles on the mechanical properties of epoxy polymers were analyzed. Nanosize platelets of boehmite powders were produced via a hydrothermal process from the raw material aluminum trihydroxide Al(OH)3 provided by a a chemical supplier, but which in future studies can be replaced by local resources of aluminum trihydroxide available in Seydisehir, Turkey. The ground aluminum trihydroxide particles were submitted to a two-step preliminary ageing procedure in different pH media. Particles were then converted to boehmite nanoparticles via hydrothermal ageing at high pressure and temperature. The product&lsquo / s chemical identity, size, structure and morphology were characterized with XRD, FT-IR, SEM and PSA analyses. By controlling the pH and the ageing time as parameters, hexagonal shaped nanoplatelets were obtained with dimensions ranging from 100 to 500 nm. Aiming at using these nanoparticles into surface coating polymers, the most favorable shape is the plate-like morphology, leading to adopting the last hydrothermal condition in the rest of the study. v The boehmite crystal surfaces are furnished with hydroxyls which can potentially be reacted with epoxy monomers of bisphenol A diglycidyl ether with the help of tin (II) chloride as catalyst through ring-opening reactions. The FT-IR and quantitative analyses indicated that this surface functionalization is possible under a temperature 80 oC and a weight ratio of 5:1 epoxy monomer to boehmite powder These novel inorganic/organic hybrid materials were then mixed with epoxy/hardener resin mixture to obtain nanocomposites. The properties of the composites were characterized accordingly with tensile, impact, micro hardness, micro-scratch tests, DMA analysis and observed with SEM analysis. A deterioration of the tensile strength from the neat polymer was observed, with a distinct trend between the functionalized and non-functionalized boehmite-epoxy polymers. The functionalized polymers showed a less deteriorative character. The tensile modulus instead showed a little improvement of (4%) in 5wt% loaded polymers. DMA analysis results revealed an improved glass transition temperature in the nanocomposites as well as in storage and loss modulus. As aimed in this work, the functionalized boehmite-epoxy polymers displayed a clear improvement in comparison to both non-functionalized and neat polymers in surface coating properties in hardness and scratch resistance.

No fim do século XX cresceu o interesse por materiais com potencial para aplicação na área da nanotecnologia. Um destes materiais é o grafeno (alótropo do carbono da espessura de um átomo), indicado para aplicações que exploram desde propriedades ópticas até mecânicas. Todavia, os métodos de produção estabelecidos até o momento geram normalmente um produto com alto grau de defeitos estruturais. Por isso, o objetivo deste estudo foi desenvolver um método mais brando para obtenção de grafeno, por meio do desenrolamento de nanotubos de carbono (NTC) de parede múltipla na presença de líquidos iônicos (LI) (que possuem caráter lubrificante e estabilizador) e adicioná-lo à resina epoxídica para avaliar seu efeito nas propriedades do nanocompósito. A metodologia consistiu em definir a rota a que a mistura NTC:LI (bis(trifluorometanosulfonil)imidato de 1-n-butil-3-metilimidazólio – BMImNTf2), na proporção 1:10, deveria ser submetida e depois avaliar variações para validação do método (alteração de temperatura, solventes – LI BMImCl e tolueno e nanocarga – grafite). As misturas de grafeno-NTC/LI produzidas foram adicionadas na proporção de 0,1% em massa de grafeno-NTC à resina epoxídica. A caracterização das misturas se deu pelas técnicas de microscopia eletrônica de transmissão (MET), espectroscopia Raman e microscopia de força atômica (AFM), e dos nanocompósitos, também por microscopia eletrônica de varredura (MEV), análise termogravimétrica (TGA), calorimetria diferencial exploratória (DSC), infravermelho (IV) análise dinâmico-mecânica (DMA) e ensaios mecânicos. A morfologia observada em MET e AFM evidenciou que a rota em que a mistura permaneceu 3 h em aquecimento e agitação magnética sob vácuo e 3 h sob sonificação resultou em grafeno de algumas camadas. Os resultados de Raman mostraram que foi produzido grafeno de boa qualidade, baseando-se na razão ID/IG. Nos nanocompósitos, confirmou-se que BMImNTf2 mantém as folhas de grafeno abertas. Já com BMImCl a morfologia dos NTC permanece inalterada, mas seu grau de emaranhamento é diminuído pela ação lubrificante deste LI, o que reflete em melhoria na resistência ao impacto. Os NTC sem a presença de um LI de forma geral não conferiram melhoria à matriz polimérica (ex: queda de 35% na dureza). / In the late twentieth century, the interest in materials with potential application in the nanotechnology´s field has increased. One of these materials is graphene (carbon allotrope of a single atom thickness), suitable for applications, which exploit properties such as optical or mechanical. However, the methods developed up to now to obtain graphene usually generate a product with high degree of structural defects. Therefore, the aim of this study was to produce graphene sheets through a milder route of unrolling multi-walled carbon nanotubes (CNT) in ionic liquids (IL; which have a lubricating and stabilizing character) and to add it to an epoxy resin to evaluate its effect on the nanocomposite properties. The methodology consisted of defining the route through which the 1:10 mixture of CNT:IL (1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate - BMImNTf2) should be submitted, and then evaluate possible variations for validating the method (change in temperature, solvents - toluene and IL BMImCl and nanofiller - graphite). The produced graphene-CNT/IL mixtures were added at 0.1% by weight of graphene-CNT to epoxy resin. Characterization of the graphene/IL mixtures was done by transmission electron microscopy (TEM), Raman spectroscopy and atomic force microscopy (AFM), and the nanocomposites also by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamical mechanical analysis (DMA) and mechanical tests. The morphology observed using TEM and AFM showed that the route based on 3 h under heating, stirring and vacuum, followed by 3 h of sonication leads to CNT unrolling. Raman spectra showed that the produced graphene was of good quality, based on the low ID/IG ratio. In the nanocomposites, CNT unrolling was confirmed when IL BMImNTf2 was used, yielding reasonable property improvements. In the case of IL BMImCl, the unrolling of the CNT did not occur, but the lubricant effect of the IL decreased the degree of entanglement, which increased its impact strength. Differently, the non-treated CNT generally reduced the properties of the polymer matrix, e.g. a 35% drop in hardness.

No fim do século XX cresceu o interesse por materiais com potencial para aplicação na área da nanotecnologia. Um destes materiais é o grafeno (alótropo do carbono da espessura de um átomo), indicado para aplicações que exploram desde propriedades ópticas até mecânicas. Todavia, os métodos de produção estabelecidos até o momento geram normalmente um produto com alto grau de defeitos estruturais. Por isso, o objetivo deste estudo foi desenvolver um método mais brando para obtenção de grafeno, por meio do desenrolamento de nanotubos de carbono (NTC) de parede múltipla na presença de líquidos iônicos (LI) (que possuem caráter lubrificante e estabilizador) e adicioná-lo à resina epoxídica para avaliar seu efeito nas propriedades do nanocompósito. A metodologia consistiu em definir a rota a que a mistura NTC:LI (bis(trifluorometanosulfonil)imidato de 1-n-butil-3-metilimidazólio – BMImNTf2), na proporção 1:10, deveria ser submetida e depois avaliar variações para validação do método (alteração de temperatura, solventes – LI BMImCl e tolueno e nanocarga – grafite). As misturas de grafeno-NTC/LI produzidas foram adicionadas na proporção de 0,1% em massa de grafeno-NTC à resina epoxídica. A caracterização das misturas se deu pelas técnicas de microscopia eletrônica de transmissão (MET), espectroscopia Raman e microscopia de força atômica (AFM), e dos nanocompósitos, também por microscopia eletrônica de varredura (MEV), análise termogravimétrica (TGA), calorimetria diferencial exploratória (DSC), infravermelho (IV) análise dinâmico-mecânica (DMA) e ensaios mecânicos. A morfologia observada em MET e AFM evidenciou que a rota em que a mistura permaneceu 3 h em aquecimento e agitação magnética sob vácuo e 3 h sob sonificação resultou em grafeno de algumas camadas. Os resultados de Raman mostraram que foi produzido grafeno de boa qualidade, baseando-se na razão ID/IG. Nos nanocompósitos, confirmou-se que BMImNTf2 mantém as folhas de grafeno abertas. Já com BMImCl a morfologia dos NTC permanece inalterada, mas seu grau de emaranhamento é diminuído pela ação lubrificante deste LI, o que reflete em melhoria na resistência ao impacto. Os NTC sem a presença de um LI de forma geral não conferiram melhoria à matriz polimérica (ex: queda de 35% na dureza). / In the late twentieth century, the interest in materials with potential application in the nanotechnology´s field has increased. One of these materials is graphene (carbon allotrope of a single atom thickness), suitable for applications, which exploit properties such as optical or mechanical. However, the methods developed up to now to obtain graphene usually generate a product with high degree of structural defects. Therefore, the aim of this study was to produce graphene sheets through a milder route of unrolling multi-walled carbon nanotubes (CNT) in ionic liquids (IL; which have a lubricating and stabilizing character) and to add it to an epoxy resin to evaluate its effect on the nanocomposite properties. The methodology consisted of defining the route through which the 1:10 mixture of CNT:IL (1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate - BMImNTf2) should be submitted, and then evaluate possible variations for validating the method (change in temperature, solvents - toluene and IL BMImCl and nanofiller - graphite). The produced graphene-CNT/IL mixtures were added at 0.1% by weight of graphene-CNT to epoxy resin. Characterization of the graphene/IL mixtures was done by transmission electron microscopy (TEM), Raman spectroscopy and atomic force microscopy (AFM), and the nanocomposites also by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamical mechanical analysis (DMA) and mechanical tests. The morphology observed using TEM and AFM showed that the route based on 3 h under heating, stirring and vacuum, followed by 3 h of sonication leads to CNT unrolling. Raman spectra showed that the produced graphene was of good quality, based on the low ID/IG ratio. In the nanocomposites, CNT unrolling was confirmed when IL BMImNTf2 was used, yielding reasonable property improvements. In the case of IL BMImCl, the unrolling of the CNT did not occur, but the lubricant effect of the IL decreased the degree of entanglement, which increased its impact strength. Differently, the non-treated CNT generally reduced the properties of the polymer matrix, e.g. a 35% drop in hardness.

No fim do século XX cresceu o interesse por materiais com potencial para aplicação na área da nanotecnologia. Um destes materiais é o grafeno (alótropo do carbono da espessura de um átomo), indicado para aplicações que exploram desde propriedades ópticas até mecânicas. Todavia, os métodos de produção estabelecidos até o momento geram normalmente um produto com alto grau de defeitos estruturais. Por isso, o objetivo deste estudo foi desenvolver um método mais brando para obtenção de grafeno, por meio do desenrolamento de nanotubos de carbono (NTC) de parede múltipla na presença de líquidos iônicos (LI) (que possuem caráter lubrificante e estabilizador) e adicioná-lo à resina epoxídica para avaliar seu efeito nas propriedades do nanocompósito. A metodologia consistiu em definir a rota a que a mistura NTC:LI (bis(trifluorometanosulfonil)imidato de 1-n-butil-3-metilimidazólio – BMImNTf2), na proporção 1:10, deveria ser submetida e depois avaliar variações para validação do método (alteração de temperatura, solventes – LI BMImCl e tolueno e nanocarga – grafite). As misturas de grafeno-NTC/LI produzidas foram adicionadas na proporção de 0,1% em massa de grafeno-NTC à resina epoxídica. A caracterização das misturas se deu pelas técnicas de microscopia eletrônica de transmissão (MET), espectroscopia Raman e microscopia de força atômica (AFM), e dos nanocompósitos, também por microscopia eletrônica de varredura (MEV), análise termogravimétrica (TGA), calorimetria diferencial exploratória (DSC), infravermelho (IV) análise dinâmico-mecânica (DMA) e ensaios mecânicos. A morfologia observada em MET e AFM evidenciou que a rota em que a mistura permaneceu 3 h em aquecimento e agitação magnética sob vácuo e 3 h sob sonificação resultou em grafeno de algumas camadas. Os resultados de Raman mostraram que foi produzido grafeno de boa qualidade, baseando-se na razão ID/IG. Nos nanocompósitos, confirmou-se que BMImNTf2 mantém as folhas de grafeno abertas. Já com BMImCl a morfologia dos NTC permanece inalterada, mas seu grau de emaranhamento é diminuído pela ação lubrificante deste LI, o que reflete em melhoria na resistência ao impacto. Os NTC sem a presença de um LI de forma geral não conferiram melhoria à matriz polimérica (ex: queda de 35% na dureza). / In the late twentieth century, the interest in materials with potential application in the nanotechnology´s field has increased. One of these materials is graphene (carbon allotrope of a single atom thickness), suitable for applications, which exploit properties such as optical or mechanical. However, the methods developed up to now to obtain graphene usually generate a product with high degree of structural defects. Therefore, the aim of this study was to produce graphene sheets through a milder route of unrolling multi-walled carbon nanotubes (CNT) in ionic liquids (IL; which have a lubricating and stabilizing character) and to add it to an epoxy resin to evaluate its effect on the nanocomposite properties. The methodology consisted of defining the route through which the 1:10 mixture of CNT:IL (1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate - BMImNTf2) should be submitted, and then evaluate possible variations for validating the method (change in temperature, solvents - toluene and IL BMImCl and nanofiller - graphite). The produced graphene-CNT/IL mixtures were added at 0.1% by weight of graphene-CNT to epoxy resin. Characterization of the graphene/IL mixtures was done by transmission electron microscopy (TEM), Raman spectroscopy and atomic force microscopy (AFM), and the nanocomposites also by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamical mechanical analysis (DMA) and mechanical tests. The morphology observed using TEM and AFM showed that the route based on 3 h under heating, stirring and vacuum, followed by 3 h of sonication leads to CNT unrolling. Raman spectra showed that the produced graphene was of good quality, based on the low ID/IG ratio. In the nanocomposites, CNT unrolling was confirmed when IL BMImNTf2 was used, yielding reasonable property improvements. In the case of IL BMImCl, the unrolling of the CNT did not occur, but the lubricant effect of the IL decreased the degree of entanglement, which increased its impact strength. Differently, the non-treated CNT generally reduced the properties of the polymer matrix, e.g. a 35% drop in hardness.

<div> <p><a>Polymer nanocomposites are envisioned for use in many advanced applications, such as structural industries, aerospace, automotive technology and electronic materials, due to the improved properties like mechanical strengthening, thermal and chemical stability, easy bulk processing, and/or light-weight instigated by the filler-matrix combination compared to the neat matrix. In recent years, due to increasing environmental concerns, many industries are inclining towards developing sustainable and renewable polymer nanocomposites. Cellulose nanomaterials (CNs), including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), have gained popularity due to their excellent mechanical properties and eco-friendliness (extracted from trees, algae, plants etc.). However, to develop CN-reinforced nanocomposites with industrial applications it is necessary to understand impact of hygroscopic swelling (which has very limited </a>quantitative study at present), aspect ratio, orientation, and content of CNs on the overall performance of nanocomposites; and overcome the low dispersibility of CNs and improve their compatibility with hydrophobic matrix. In this work, we attempt to understand the influence of single nanocrystals in the hygroscopic and optical response exhibited by nanostructured films; effect of CNCs on the properties of PVA/CNC fibers by experimental evidence with mathematical modeling predictions; and hydrophobized CNFs using a facile, aqueous surface modification to improve interfacial compatibility with epoxy. </p><p><br></p> <p>To evaluate the effect of CNC alignment in the bulk response to hygroscopic expansion, self-organized and shear-oriented CNC films were prepared under two different mechanisms. The coefficient of hygroscopic swelling (CHS) of these films was determined by using a new contact-free method of Contrast Enhanced Microscopy Digital Image Correlation (CEMDIC) that enabled the characterization of dimensional changes induced by hygroscopic swelling of the films. This method can be readily used for other soft materials to accurately measure hygroscopic strain in a non-destructive way. By calculating the CHS values of CNC films, it was determined that hygroscopic swelling is highly dependent on the alignment of nanocrystals within the films, with aligned CNC films showing dramatically reduced hygroscopic expansion than randomly oriented films. Finite element analysis was used to simulate moisture sorption and kinetics profile which further predicted moisture diffusion as the predominant mechanism for swelling of CNC films. </p> <p><br></p><p>To study the effects of different types and aspect ratios of CNCs on mechanical, thermal and morphological properties of polyvinyl alcohol (PVA) composite <a>fibers, CNCs extracted from wood pulp and cotton were reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with first stage drawing up to draw ratio 2. </a>The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5 – 15 wt. %) at the expense of their strain-to-failure. The mechanical properties of fibers with cotton CNC were higher than the fibers with wood CNC when the same amount of CNCs were added due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the composite fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.</p><p><br></p> <p>To improve the dispersibility and compatibility of CNFs with epoxy, CNFs were modified by using a two-step water-based method where tannic acid (TA) acts as a primer with CNF suspension and reacts with hexadecylamine (HDA), forming the modified product as CNF-TA-HDA. The modified (-m) and unmodified (-um) CNFs were filled into hydrophobic epoxy resin with a co-solvent (acetone), which was subsequently removed to form a solvent-free two component epoxy system, followed by addition of hardener to cure the resin. Better dispersion and stronger adhesion between fillers and epoxy were obtained for m-CNF than the um-CNF, resulting in better mechanical properties of nanocomposites at the same loading. Thermal stability and the degradation temperature of m-CNF/epoxy improved when compared to neat epoxy. </p> </div> <br>

Polymers are widely used as insulating materials in high voltage power apparatus because of their excellent electrical insulating properties and good thermomechanical behavior. However, under high electrical stress, polymeric materials can get deteriorated which can eventually lead to the failure of the insulation and thereby the power apparatus. Electrical treeing is one such phenomena whereby dendritic paths progressively grow from a region of high electrical stress and branch into conducting channels in a solid dielectric. The propagation of electrical trees is of particular interest for the power industry as it is one of the major causes of failure of high voltage insulation especially in high voltage cables, cast resin transformers as well as rotating machines. To improve the life time of the electrical insulation systems there is a need to improve the electrical treeing resistance of the insulating material for high voltage application. With the development of nanotechnology, polymer nanocomposites containing nano sized particles have drawn much attention as these materials are found to exhibit unique combinations of physical, mechanical and thermal properties that are advantageous as compared to the traditional polymers or their composites. Literature reveals that significant progress has been made with respect to the mechanical, optical, electronic and photonic properties of these functional materials. Some efforts have also been directed towards the study of dielectric/electrical insulation properties of these new types of materials. Considering the above facts, the present research work focuses on utilizing these new opportunities which have been opened up by the advent of nanocomposites to develop tree resistant insulating materials for high voltage power applications. Electrical treeing is a common failure mechanism in most of the polymeric insulation systems and hence electrical treeing studies have been carried out on two types of polymers (viz. polyethylene used in high voltage cable and epoxy used in rotating machines and resin cast transformers) along with three different types of nano-fillers, viz. Al2O3, SiO2 and MgO and with different filler loadings (0.1, 1, 3, 5 wt%). Furthermore, considering the fact that electrical treeing is a discharge phenomenon, the partial discharge characteristics during electrical tree growth in polymer nanocomposites was studied. As morphological changes in the polymer influence the electrical tree growth, the influence of nano-particle induced morphological changes on the electrical treeing has also been studied. Above all, an attempt has also been made to characterize and analyze the interaction dynamics at the interface regions in the polymer nanocomposite and the influence of these interface regions on the tree growth phenomena in polymer nanocomposites. A laboratory based nanocomposite processing method has been successfully designed and adopted to prepare the samples for treeing studies. Treeing experimental results show that there is a significant improvement in tree initiation time as well as tree inception voltage with nano-filler loading in polymer nanocomposites. It is observed that even with the addition of a small amount (0.1 and 1 % by weight) of nano-particles to epoxy results in the improvement of electrical treeing resistance as compared to the unfilled epoxy. In fact, different tree growth patterns were observed for the unfilled epoxy and epoxy nanocomposites. Surprisingly, even though there is not much improvement in tree inception time, a saturation tendency in tree growth with time was observed at higher filler loadings. To understand the influence of nano-particles on electrical treeing, the interaction dynamics in the epoxy nanocomposites were studied and it was shown that the nature of the bonding at the interface play an important role on the electrical tree growth in epoxy nanocomposites. The results of electrical treeing experiments in polyethylene nanocomposites obtained in this study also reveal some interesting findings. An improved performance of polyethylene against electrical treeing with the inclusion of nano-fillers is observed. It is observed that there is a significant improvement in the tree inception voltage even with low nano-filler loadings in polyethylene. Other interesting results such as change in tree growth pattern from branch to bush as well as slower tree growth with increase in filler loading were also observed. Another peculiar observation is that tree inception voltage increased with increase in filler loading upto a certain filler loadings (3 % by weight) and then decreased in its value at high filler loading. The morphology of polyethylene nanocomposites was studied and a good correlation between morphological changes and treeing results was observed. Effect of cross-linking on electrical treeing has also been studied and a better performance of cross-linking of nano-filled polyethylene samples as compared to the polyethylene samples without cross-linking was observed. The partial discharge (PD) activity during electrical tree growth was monitored and different PD characteristics for unfilled and nano-filled polyethylene samples were observed. Interestingly, a decrease in PD magnitude as well as the number of PD pulses with electrical tree growth in polyethylene nanocomposites was observed. It is known that PD activity depends on the tree channel conductivity, charge trapping and gas pressure inside the tree channel. The ingress of nano-particles into the tree channel influences the above known phenomena and affects the PD activity during electrical tree growth. The observed decrease in PD magnitude with increase in filler loading leads to the slow propagation of electrical trees in polyethylene nanocomposites. In summary, it can be concluded that polymer nanocomposites performed better against electrical treeing as compared to the unfilled and the conventional micron sized filled polymer composites. Even with low filler loading an improved electrical treeing resistance was observed in polymer nanocomposites. An optimum filler loading and a suitable filler to inhibit electrical treeing in the polymers studied are proposed. This work also establishes the fact that the characteristics of the interface region and the induced morphological changes have a strong influence on the electrical treeing behaviors of nanocomposites. These encouraging results showed that epoxy and polyethylene nanocomposites can be used as tree resistant insulating materials for high voltage applications. These results also contribute to widen the scope of applications of polymer nanocomposites in electrical power sector as well as development of multifunctional insulation systems.

One of the most significant issues in nanocomposite performance is improving the dispersion of carbon nanotubes (CNTs) in thermosetting or thermoplastic polymers in order to gain good mechanical properties. Several studies have investigated the fabrication of nanocomposites based on carbon nanotubes and analysed properties, but there is still insufficient data on their structure-property relationships. This thesis has investigated the central importance of stress transfer Raman studies in epoxy composites reinforced with single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs) to elucidate the reinforcing ability of the CNTs in an epoxy matrix. This project was undertaken to synthesise and characterize MWCNTs and determine the effect of different weight fractions of untreated MWCNTs on the stress transfer efficiency at the MWCNTS / epoxy interface and on the stiffness of the thermomechanical properties of the MWCNTS / epoxy composites. It was undertaken to assess the stress transfer efficiency at the CNT / epoxy interface and at the inter-walls of the CNTs with tensile deformation and with cyclic loading.Optimized conditions of the injection chemical vapour deposition method (CVD), such as long injection times were applied to produce MWCNTs with a high yield, high aspect ratio and well-defined G' Raman peak. The morphology and size of CNTs were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) while their thermal stability was examined by Thermogravimetric analysis (TGA). Both Raman spectroscopy and mechanical testing (static and dynamic) were utilized in this study. The Raman spectroscopy research consisted of following the G'-band frequency and linewidth as well as the intensity of radial breathing modes (RBMs) during tensile deformation. The stress-induced Raman shifts in the nanocomposites have been shown to be controlled by the number of carbon nanolayers. A theory has been developed to determine and simulate the stress transfer efficiency parameter, (k_i) for MWCNTs. Tensile tests and dynamic mechanical testing were used to assess the mechanical properties of the nanocomposites.The most obvious finding to be drawn from the present study is that the reinforcement of the epoxy resin with different loadings of MWCNTs is useful, but the best reinforcement was at low loadings of MWCNTs. One of the more significant findings to emerge from this study is that (k_i) between the inner walls of the DWCNTs and MWCNTs are quite similar (~0.7), which suggest that (k_i) may be similar for all CVD MWCNTs and DWCNTs. The second major finding was that there were RBM intensity variations for the SWCNTs and DWCNTs in the hot-cured epoxy composites and that for the DWCNTs both the inner and outer nanotube walls are stressed during deformation

Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost. The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers. The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller. The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications. The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres. From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface. For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites. Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan  and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan  values were calculated with duration of aging. It was observed that the tan  values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.