Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-15Bitstream added on 2014-06-13T19:00:09Z : No. of bitstreams: 1 salmazo_lo_me_bauru.pdf: 5230553 bytes, checksum: a59e34c0fc1acb2b0b0e6406f5258087 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O objetivo deste trabalho foi sintetizar nanopartículas monofásicas paramagnéticas de ferrita de níquel e zinco, Ni0,5Zn0,5Fe2O4 (NZF) e utilizá-las na preparação de filmes elastoméricos calcinadas em diferentes temperaturas de forma a modificar seu tamanho. A caracterização estrutural das nanopartículas foi realizada via espectroscopia vibracional de absorção na região do infravermelho (FTIR), onde foi possível investigar as vibrações características da fase tipo espinélio entre 500 e 600 cm-¹ e 400 cm-¹, difratometria de raios X (DRX), microscopia eletrônica de transmissão (MET), no qual foi possível identificar a formação de nanopartículas monofásicas de Ni0,5Zn0,5FeO4 de acordo com ficha JCDS-08-0234, com tamanho entre 14 a 20nm. A caracterização térmica dos precursores das nanopartículas foi realizada utilizando as técnicas de calometria exploratória diferencial (DSC) e termogravimetria (TG). Nanomcompósitos com matriz de borracha natural vulcanizada foram preparados utilizando diferentes concentrações e tamanhos de nanopartículas paramagnéticas, as quais foram adicionadas aos demais componentes necessários à vulcanização da borracha natural (BN) do tipo crepe claro brasileiro. A análise estrutural dos nanocompósitos, denominados de BN/NZF, foi realizado utilizando as técnicas de difratometria de raios X (DRX), espectroscopia vibracional de absorção na região do infravermelho (FTIR), microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). Através destas técnicas, a incorporação de diferentes proporções e tamanhos de nanopartículas foi avaliada. A caracterização térmica dos nanocompósitos foi realizada utilizando as ténicas de calorimetria exploratória diferencial (DSC), termogravimetria (TG), análise dinâmico-mecânica (DMA) com intuito de... (Resumo completo, clicar acesso eletrônico abaix / This project aims to the synthesis of single-phase paramagnetic nanoparticles of Ni0,5Zn0,5Fe2O4 (NZF) nickel zinc ferrite and its application in the development of functional nanocomposites in specific materials with potential for microwave absorber. Modified Polyol method was used to synthesize a precursor powder, which was calcined at diferent temperatures in order to attain nanoparticles with different size particles. Structural characterization of nanoparticles was carried out by absorption spectroscopy in the infrared region with Fourier Transformed (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (MET). From FTIR technique was possible to investigate chemical bonds and the Ni0,5Zn0,5Fe2O4 phase formation. The evolution of the thermal behavior of both precursor powder and nanoparticles was performed using the differential scanning calorimetry (DSC) and thermogravimetry (TG). Nanocomposites of vulcanized natural rubber were prepared using different concentration of Ni0,5Zn0,5Fe2O4 nanoparticles, which were added to other components necessary to the vulcanization process of natural rubber (NR), Hevea brasiliensis - clone RRIM 600. The structural analysis of nanocomposites of vulcanized natural rubber containing as additives different fractions of nickel zinc ferrite called here as NR/NZF was conducted by use of techniques: XRD, FTIR, optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thermal analyses of nanocomposites were performed using DSC, TG, dynamic mechanical analysis (DMA) in order to identify changes in behavior of vulcanized natural rubber, as a function of fraction of Ni0,5Zn0,5FeO4 nanoparticles. The magnetic behavior of both nanoparticles and nanocomposites were investigated by the vibrating sample magnetometer... (Complete abstract click electronic access below)

Orientador: Aldo Eloizo Job / Banca: Marcos Augusto de Lima Nobre / Banca: Mariselma Ferreira / O programa de Pós graduação em Ciência e Tecnologia de Materiais, POSMAT, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi da UNESP / Resumo: O objetivo deste trabalho foi sintetizar nanopartículas monofásicas paramagnéticas de ferrita de níquel e zinco, Ni0,5Zn0,5Fe2O4 (NZF) e utilizá-las na preparação de filmes elastoméricos calcinadas em diferentes temperaturas de forma a modificar seu tamanho. A caracterização estrutural das nanopartículas foi realizada via espectroscopia vibracional de absorção na região do infravermelho (FTIR), onde foi possível investigar as vibrações características da fase tipo espinélio entre 500 e 600 cm-¹ e 400 cm-¹, difratometria de raios X (DRX), microscopia eletrônica de transmissão (MET), no qual foi possível identificar a formação de nanopartículas monofásicas de Ni0,5Zn0,5FeO4 de acordo com ficha JCDS-08-0234, com tamanho entre 14 a 20nm. A caracterização térmica dos precursores das nanopartículas foi realizada utilizando as técnicas de calometria exploratória diferencial (DSC) e termogravimetria (TG). Nanomcompósitos com matriz de borracha natural vulcanizada foram preparados utilizando diferentes concentrações e tamanhos de nanopartículas paramagnéticas, as quais foram adicionadas aos demais componentes necessários à vulcanização da borracha natural (BN) do tipo crepe claro brasileiro. A análise estrutural dos nanocompósitos, denominados de BN/NZF, foi realizado utilizando as técnicas de difratometria de raios X (DRX), espectroscopia vibracional de absorção na região do infravermelho (FTIR), microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). Através destas técnicas, a incorporação de diferentes proporções e tamanhos de nanopartículas foi avaliada. A caracterização térmica dos nanocompósitos foi realizada utilizando as ténicas de calorimetria exploratória diferencial (DSC), termogravimetria (TG), análise dinâmico-mecânica (DMA) com intuito de... (Resumo completo, clicar acesso eletrônico abaix / Abstract: This project aims to the synthesis of single-phase paramagnetic nanoparticles of Ni0,5Zn0,5Fe2O4 (NZF) nickel zinc ferrite and its application in the development of functional nanocomposites in specific materials with potential for microwave absorber. Modified Polyol method was used to synthesize a precursor powder, which was calcined at diferent temperatures in order to attain nanoparticles with different size particles. Structural characterization of nanoparticles was carried out by absorption spectroscopy in the infrared region with Fourier Transformed (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (MET). From FTIR technique was possible to investigate chemical bonds and the Ni0,5Zn0,5Fe2O4 phase formation. The evolution of the thermal behavior of both precursor powder and nanoparticles was performed using the differential scanning calorimetry (DSC) and thermogravimetry (TG). Nanocomposites of vulcanized natural rubber were prepared using different concentration of Ni0,5Zn0,5Fe2O4 nanoparticles, which were added to other components necessary to the vulcanization process of natural rubber (NR), Hevea brasiliensis - clone RRIM 600. The structural analysis of nanocomposites of vulcanized natural rubber containing as additives different fractions of nickel zinc ferrite called here as NR/NZF was conducted by use of techniques: XRD, FTIR, optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thermal analyses of nanocomposites were performed using DSC, TG, dynamic mechanical analysis (DMA) in order to identify changes in behavior of vulcanized natural rubber, as a function of fraction of Ni0,5Zn0,5FeO4 nanoparticles. The magnetic behavior of both nanoparticles and nanocomposites were investigated by the vibrating sample magnetometer... (Complete abstract click electronic access below) / Mestre

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Foi preparado o nanocompósito de borracha natural/argila chocolate B modificada por sodificação via seca com variação no processo, utilizando silicato de sódio ao invés de carbonato de sódio e tratada com sal quaternário de amônio, cloreto hexadecil trimetil amônio. A argila no seu estado natural, após sodificação e após quaternização foi caracterizada pelas técnicas de microscopia estereoscópica, análise térmica, infravermelho, difração de raios X e microscopia eletrônica de varredura. Outras cargas orgânicas foram adicionadas, como celulose e piaçava e comparadas com cargas tradicionais, como o negro de fumo. As placas obtidas, após vulcanização, tiveram medidas as suas propriedades mecânicas e foram analisadas por DRX e MEV. Os nanocompósitos obtidos mostraram melhoria nas suas propriedades mecânicas em comparação com as placas sem a adição de argila. / The natural rubber/clay chocolate B nanocomposite modified by dry sodification process with variation processing was prepared using sodium silicate instead of sodium carbonate and treated with quaternary ammonium salt, hexadecyl trimethyl ammonium chloride. The clay in its natural state after sodification and after quaternization was characterized by the techniques of stereoscopic microscopy, thermal analysis, infrared, X-ray diffraction and scanning electron microscopy. Other organic fillers were added, such as cellulose and piaçava, and compared with traditional fillers such as carbon black. The plates obtained after vulcanization had their mechanical properties measured and were analyzed by XRD and SEM. The obtained nanocomposites showed improvement in their mechanical properties in comparison with the plates without the addition of clay.

Foi preparado o nanocompósito de borracha natural/argila chocolate B modificada por sodificação via seca com variação no processo, utilizando silicato de sódio ao invés de carbonato de sódio e tratada com sal quaternário de amônio, cloreto hexadecil trimetil amônio. A argila no seu estado natural, após sodificação e após quaternização foi caracterizada pelas técnicas de microscopia estereoscópica, análise térmica, infravermelho, difração de raios X e microscopia eletrônica de varredura. Outras cargas orgânicas foram adicionadas, como celulose e piaçava e comparadas com cargas tradicionais, como o negro de fumo. As placas obtidas, após vulcanização, tiveram medidas as suas propriedades mecânicas e foram analisadas por DRX e MEV. Os nanocompósitos obtidos mostraram melhoria nas suas propriedades mecânicas em comparação com as placas sem a adição de argila. / The natural rubber/clay chocolate B nanocomposite modified by dry sodification process with variation processing was prepared using sodium silicate instead of sodium carbonate and treated with quaternary ammonium salt, hexadecyl trimethyl ammonium chloride. The clay in its natural state after sodification and after quaternization was characterized by the techniques of stereoscopic microscopy, thermal analysis, infrared, X-ray diffraction and scanning electron microscopy. Other organic fillers were added, such as cellulose and piaçava, and compared with traditional fillers such as carbon black. The plates obtained after vulcanization had their mechanical properties measured and were analyzed by XRD and SEM. The obtained nanocomposites showed improvement in their mechanical properties in comparison with the plates without the addition of clay.

During the last years rubber nanocomposites obtained by incorporating anisotropic clay nanoparticles within a rubber matrix to tailor material properties have attracted steadily growing interest. However, one main complication preventing rubber-clay nanocomposites from many potential applications is the difficulty to achieve a high degree of exfoliation particularly in case of melt mixing or compounding (using mixing equipment like internal mixer, two roll mills which can be up-scaled in industry). Albeit commercially available organomodified montmorillonite clays (OMt) are fairly compatible with the polar rubber like Acrylo-nitrile butadiene rubber (NBR), carboxylated nitrile rubber (XNBR), chloroprene rubber (CR) etc., its dispersion in non-polar rubbers like natural rubber (NR), is rather unsatisfactory. Incorporation of only 5 phr of OMt in NR by mechanical mixing leads to very poor dispersions with larger aggregates. Large agglomerates of OMt were observed with bare eyes throughout the matrix. Even in the TEM micrographs, highly agglomerated structures of clay particle were observed. A high degree of exfoliation of such clay is achieved in NR utilizing the so called ‘Propping-open approach’ where stepwise expansion of interlayer spacing of Mt took place. A series of long chain fatty acids (C16-C22) are intercalated into the interlayer space of OMt and a gradual expansion of the interlayer space were observed as the chain length of the fatty acid increased. Wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement indicated successful intercalation of the fatty acids into the interlayer space of the clay minerals. Since the fatty acid containing 22 carbon atoms has the largest interlayer distance among the modified samples studied, it has been selected for further study to understand the reinforcing behavior in NR matrix. An unusual mechanical percolation behavior of EOMt nanoparticles was observed in a NR matrix. The value of the mechanical percolation threshold (φp) and the fractal nature of nanoparticle clusters were determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. This phenomenon was discussed in terms of fractal dimensions of the nanoparticle cluster. The impact of filler dispersion and rubber-filler interactions on the viscoelastic behavior of NR nanocomposites was systematically investigated. Significant non-linear viscoelastic behavior (Payne effect) was observed at very low EOMt content. Kraus and Maier-Göritz models were utilized to interpret such non-linear viscoelastic behavior. The nanocomposites showed enormous improvement in different physic-mechanical properties in the presence of EOMt. Technical elastomers are generally filled with certain fillers (e.g. carbon black) in order to reinforce the rubber matrix for some typical applications like tires, conveyer belts etc. Such rubber goods are always exposed to cyclic stress and deformations attributed to their dynamic application. Under constant and repeated applied stress, cracks develop at a stress concentration point, which could lead to ultimate failure. Therefore, the crack initiation and propagation behavior in such rubber products is very fundamental and need proper attention. The role of EOMt nanoparticles on the microstructure and fracture mechanical behavior of CB filled NR composites was investigated. Using pure-shear test specimen tear fatigue analysis (TFA) tests under cyclic conditions were carried out to explicate the crack growth behavior of CB filled NR in the presence of EOMt. A significant reduction in crack growth rate was noticed in the presence of only 5 phr of EOMt. Furthermore, instrumented tensile-impact tests (IT-IT) were also performed for the characterization of the crack resistance of the materials under impact-like loading conditions. / Die Einarbeitung von nur 5 phr organisch modifizierten Montmorillonite (OMt) in Naturkautschuk (NR) durch mechanisches Mischen führt zu einer sehr schlechten Verteilung mit größeren Aggregaten. Große Agglomerate von OMt waren mit bloßem Auge in der NR Matrix sichtbar. Sogar in TEM Aufnahmen wurden stark agglomerierte Strukturen beobachtet. Ein hoher Grad der Exfolierung von diesem Clay in NR wird durch die Nutzung des so genannten ‘Propping-open’ Ansatzes erreicht, in dem eine stufenweise Aufweitung des Zwischenschichtabstandes des OMt stattfindet. Eine Reihe langkettiger Fettsäuren (C16 – C22) wurde in die Zwischenschicht des OMt eingefügt. Mit zunehmender Kettenlänge der Fettsäuren wurde eine allmähliche Aufweitung der Zwischenschicht beobachtet. Da OMt, der mit einer Fettsäure mit 22 Kohlenstoffatomen modifiziert wurde, den größten Zwischenschichtabstand aller untersuchten Proben hatte, wurde diese Fettsäure für die weiteren Untersuchungen ausgewählt, um das Verstärkungsverhalten in der NR Matrix zu verstehen. Ein ungewöhliches Perkolationsverhalten der expandierten OMt (EOMt) Nanopartikel wurde in einer NR Matrix beobachtet. Der Wert der mechanischen Perkolationsschwelle (φp) und die fraktale Natur der Nanopartikel Cluster wurden durch eine Analyse der experimentellen Daten bestimmt, wobei eine Theorie, die von Huber und Vilgis vorangetrieben wurde, zur Anwendung kam. Dieses Phänomen wurde in Bezug auf die fraktalen Dimensionen der Nanopartikel Cluster diskutiert. Die Einfluss von EOMt Nanopartikel auf die Mikrostruktur und das mechanische Bruchverhalten von russgefüllten NR Kompositen wurde untersucht. Unter Verwendung reiner Schertestproben wurden Rissermüdungsanalysen unter zyklischer Belastung ausgeführt, um das Risswachstumsverhalten von russgefülltem NR in der Gegenwart von EOMt zu untersuchen und zu erklären. Eine signifikante Reduktion der Rissausbreitungsrate wurde in Gegenwart von nur 5 phr EOMt erreicht. Des Weiteren wurden auch instrumentierte Schlagzugprüfungen zur Charakterisierung des Risswiderstandes von Materialien unter schlagartigen Belastungsbedingungen durchgeführt.

During the last years rubber nanocomposites obtained by incorporating anisotropic clay nanoparticles within a rubber matrix to tailor material properties have attracted steadily growing interest. However, one main complication preventing rubber-clay nanocomposites from many potential applications is the difficulty to achieve a high degree of exfoliation particularly in case of melt mixing or compounding (using mixing equipment like internal mixer, two roll mills which can be up-scaled in industry). Albeit commercially available organomodified montmorillonite clays (OMt) are fairly compatible with the polar rubber like Acrylo-nitrile butadiene rubber (NBR), carboxylated nitrile rubber (XNBR), chloroprene rubber (CR) etc., its dispersion in non-polar rubbers like natural rubber (NR), is rather unsatisfactory. Incorporation of only 5 phr of OMt in NR by mechanical mixing leads to very poor dispersions with larger aggregates. Large agglomerates of OMt were observed with bare eyes throughout the matrix. Even in the TEM micrographs, highly agglomerated structures of clay particle were observed. A high degree of exfoliation of such clay is achieved in NR utilizing the so called ‘Propping-open approach’ where stepwise expansion of interlayer spacing of Mt took place. A series of long chain fatty acids (C16-C22) are intercalated into the interlayer space of OMt and a gradual expansion of the interlayer space were observed as the chain length of the fatty acid increased. Wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement indicated successful intercalation of the fatty acids into the interlayer space of the clay minerals. Since the fatty acid containing 22 carbon atoms has the largest interlayer distance among the modified samples studied, it has been selected for further study to understand the reinforcing behavior in NR matrix. An unusual mechanical percolation behavior of EOMt nanoparticles was observed in a NR matrix. The value of the mechanical percolation threshold (φp) and the fractal nature of nanoparticle clusters were determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. This phenomenon was discussed in terms of fractal dimensions of the nanoparticle cluster. The impact of filler dispersion and rubber-filler interactions on the viscoelastic behavior of NR nanocomposites was systematically investigated. Significant non-linear viscoelastic behavior (Payne effect) was observed at very low EOMt content. Kraus and Maier-Göritz models were utilized to interpret such non-linear viscoelastic behavior. The nanocomposites showed enormous improvement in different physic-mechanical properties in the presence of EOMt. Technical elastomers are generally filled with certain fillers (e.g. carbon black) in order to reinforce the rubber matrix for some typical applications like tires, conveyer belts etc. Such rubber goods are always exposed to cyclic stress and deformations attributed to their dynamic application. Under constant and repeated applied stress, cracks develop at a stress concentration point, which could lead to ultimate failure. Therefore, the crack initiation and propagation behavior in such rubber products is very fundamental and need proper attention. The role of EOMt nanoparticles on the microstructure and fracture mechanical behavior of CB filled NR composites was investigated. Using pure-shear test specimen tear fatigue analysis (TFA) tests under cyclic conditions were carried out to explicate the crack growth behavior of CB filled NR in the presence of EOMt. A significant reduction in crack growth rate was noticed in the presence of only 5 phr of EOMt. Furthermore, instrumented tensile-impact tests (IT-IT) were also performed for the characterization of the crack resistance of the materials under impact-like loading conditions. / Die Einarbeitung von nur 5 phr organisch modifizierten Montmorillonite (OMt) in Naturkautschuk (NR) durch mechanisches Mischen führt zu einer sehr schlechten Verteilung mit größeren Aggregaten. Große Agglomerate von OMt waren mit bloßem Auge in der NR Matrix sichtbar. Sogar in TEM Aufnahmen wurden stark agglomerierte Strukturen beobachtet. Ein hoher Grad der Exfolierung von diesem Clay in NR wird durch die Nutzung des so genannten ‘Propping-open’ Ansatzes erreicht, in dem eine stufenweise Aufweitung des Zwischenschichtabstandes des OMt stattfindet. Eine Reihe langkettiger Fettsäuren (C16 – C22) wurde in die Zwischenschicht des OMt eingefügt. Mit zunehmender Kettenlänge der Fettsäuren wurde eine allmähliche Aufweitung der Zwischenschicht beobachtet. Da OMt, der mit einer Fettsäure mit 22 Kohlenstoffatomen modifiziert wurde, den größten Zwischenschichtabstand aller untersuchten Proben hatte, wurde diese Fettsäure für die weiteren Untersuchungen ausgewählt, um das Verstärkungsverhalten in der NR Matrix zu verstehen. Ein ungewöhliches Perkolationsverhalten der expandierten OMt (EOMt) Nanopartikel wurde in einer NR Matrix beobachtet. Der Wert der mechanischen Perkolationsschwelle (φp) und die fraktale Natur der Nanopartikel Cluster wurden durch eine Analyse der experimentellen Daten bestimmt, wobei eine Theorie, die von Huber und Vilgis vorangetrieben wurde, zur Anwendung kam. Dieses Phänomen wurde in Bezug auf die fraktalen Dimensionen der Nanopartikel Cluster diskutiert. Die Einfluss von EOMt Nanopartikel auf die Mikrostruktur und das mechanische Bruchverhalten von russgefüllten NR Kompositen wurde untersucht. Unter Verwendung reiner Schertestproben wurden Rissermüdungsanalysen unter zyklischer Belastung ausgeführt, um das Risswachstumsverhalten von russgefülltem NR in der Gegenwart von EOMt zu untersuchen und zu erklären. Eine signifikante Reduktion der Rissausbreitungsrate wurde in Gegenwart von nur 5 phr EOMt erreicht. Des Weiteren wurden auch instrumentierte Schlagzugprüfungen zur Charakterisierung des Risswiderstandes von Materialien unter schlagartigen Belastungsbedingungen durchgeführt.

Outdoor electrical insulator is one of the important components of a power system which directly influences the system reliability. Traditionally ceramic insulators have been used for close to a century in both transmission and distribution lines. In the last few decades, polymer based outdoor insulators are being increasingly used in the above application. Polymeric insulators offer attractive advantages such as light weight, resistance to vandalism and they also outperform conventional ceramic insulators under contaminated wet conditions at least in the initial stages of their usage. However, there are certain disadvantages with polymeric insulators which have made the utilities hesitant to replace readily the ceramic insulators with polymeric insulators. One of the major concerns with the polymeric insulators is the aging w.r.t time due to the presence of multiple environmental stresses (fog, humidity, temperature, rain as well as contamination due to industrial, sea and agricultural pollution) along with electrical stress. The manifestations of the aging of insulators include tracking or/and erosion of the weathersheds. Polymers in pure form (unfilled) can not perform satisfactorily all the required functions (electrical, mechanical, thermal etc.) of an insulator used in such high voltage transmission lines. Polymers have inherently poor thermal stability. Thermal stability directly influences the tracking and erosion resistance of the weathershed. Without adequate tracking and erosion resistance, polymeric insulators can not perform satisfactorily under contaminated wet conditions. Hence the common practice to improve the tracking and erosion resistance (and other properties such as mechanical, thermal) is by filling the base polymer with large loadings (> 30 wt %) of micron sized fillers. This makes the processing of the polymer composite difficult as the viscosity of the material rises substantially at such large loadings. Due to the large filler loadings beyond a certain limit, the flexibility of the end product also suffers. Though tracking and erosion resistance of the polymer has been improved substantially at these large filler loadings, the recent failures in the field suggest the need for an alternate material with higher tracking and erosion resistance than what is achieved at these large loadings of micron sized fillers. Of late nanocomposites are emerging as promising alternatives which can offer the above mentioned functionalities at low filler loadings itself without sacrificing the flexibility in the end product as well as ease of processing. There are even indications suggesting that the tracking and erosion resistance performance is better than what is obtained using micronsized fillers. As the development of nanocomposite dielectrics/insulation is still at its infancy, it is required to investigate their specific properties needed for outdoor applications and to understand the various mechanisms responsible for the interesting behaviour of the nanocomposites. Also, it is known that dc pollution performance of ceramic insulators is much inferior to the performance under ac stress. With the introduction of higher ac/dc transmission voltages in many countries including India, it is required to design insulators with better performing materials so as to get a reliable performance under polluted wet conditions. Due to the hydrophobic nature of the polymers, it is believed that polymers especially silicone rubber insulators can perform better as compared to the ceramic insulators under polluted conditions under ac and dc. As the dc tracking and erosion (T&E) resistance of polymer is poor compared to the ac tracking and erosion resistance, it is required to investigate the T&E resistance characteristics of the nanocomposites under dc stress. In addition, due to the enhanced electric fields at the line end of the insulators in extra and ultra high voltage transmission lines, there is always a possibility of corona generation on the hardware at the metal-sheath junction and at the water droplet tips on the weathersheds of the polymeric insulators especially under foul weather conditions. It is reported that the long-term exposure to such corona has the potential to degrade the polymeric material. The effects include reduction of the hydrophobicity, surface oxidation of the weathersheds and development of microcracks on the surface of the polymeric material. These cracks (corona cutting) can worsen the wet pollution performance of the insulator. If the cracks grow deeper, then FRP rod would get exposed to the atmospheric conditions leading to brittle fracture of the FRP rod and finally resulting in the line drop. Hence, the corona aging resistance of nanocomposites has also been studied especially at low filler concentrations to see its performance under the above mentioned adverse conditions. Therefore, the research work presented here deals with three aspects of the aging (1) Study the ac and dc tracking and erosion resistance performance of silicone rubber nanocomposites with low concentrations of fillers and their suitability for outdoor applications (2) Study the corona aging performance of silicone rubber nanocomposites with low concentrations of fillers and (3) To develop a model to explain the unusual behaviour of nanocomposites observed in the above studies. The thesis also reports results of the accelerated multistress weathering studies conducted on normal polymeric outdoor insulators under prolonged dry conditions. The major challenge in case of the polymer nanocomposite processing is getting uniform distribution of the fillers. A protocol has been standardised for the processing which comprises high shear mechanical mixing followed by sonication to get good dispersion of the fillers. Room Temperature Vulcanised (RTV) silicone rubber was successfully processed with different micron and nanosized fillers and with different weight (wt.) percentages in the present work. For carrying out the T & E resistance, corona aging and multistress aging studies, facilities (such as Inclined Plane T & E Resistance Test Apparatus in line with IEC/ASTM standards and aging chambers) have been designed and developed in house as a part of the thesis work. The ac tracking and erosion resistance performance of the unfilled, microcomposite (filled with alumina trihydrate filler of 5, 10, 15, 20 and 30 % by wt) and nanocomposite (filled with alumina, silica and magnesium hydroxide fillers of 2.5 and 4 % by wt) have been compared in inclined plane (IP) tracking and erosion resistance test facility specifically developed for the work. It was very interesting to observe that nanocomposites at 4 % performed on par with the microcomposites at 30 % filler loadings. Leakage current was also measured during the IP test and it was found that the form factor (ratio of r.m.s to average leakage current) was in good agreement with the variation in the erosion resistance of the silicone rubber composites and hence it can be used as a diagnostic tool for assessing the aging state of the polymeric materials. It was also observed that the performance under positive dc stress was much inferior to the performance under ac stress. The dissipation of power under dc stress was estimated by measuring the leakage current through the sample and is found to be about four times (towards the end of the test) higher as compared to the power dissipation under ac stress. Intense electrolytic corrosion has been observed (under positive dc) on the grounded electrode and on the sample and chemical studies of the same have been carried out. The poor performance under dc is due to the absence of the voltage zero crossing, more accumulation of the contaminant (scaling) and electrolytic corrosion. It was also observed that to get the same tracking and erosion resistance under dc as in the case of ac during IP test, dc stress levels have to be reduced to about 60 % of the ac stress. This information would be helpful to the design engineer of the outdoor insulators for the HVDC transmission lines. To understand the different mechanisms responsible in improving the tracking and erosion resistance of the micro and nanocomposites, thermal, SEM and FTIR studies have been carried out. Thermal stability of the samples was measured using thermogravimetric analysis (TGA) and differential thermo gravimetric (DTG) studies. It was observed that thermal stability of nanocomposites even at low filler loadings (4 wt %) was comparable with the microcomposites at higher filler loadings (30 wt %). SEM studies indicate that the barrier resistance (against discharges) offered by the fillers in the nanocomposites even at low filler loadings (4 %) could be comparable with the microcomposites at higher filler loadings (30 %). The interaction between the fillers and the host matrix has been studied using various techniques. SEM studies done on the eroded regions of the composites revealed that a honey comb type formation had taken place on the nanocomposites during the IP test which was believed to be due to the interaction of the filler and the polymer. This honey comb structure formation at the eroded site in the nanocomposites greatly helps to protect the sample from further damage due to the discharges. The interaction at the interface between the polymer and fillers could also lead to further improvement in the thermal stability of the nanocomposite. A model was proposed which considers barrier resistance and a single-layer interaction around the fillers to explain the improvements offered by the nanocomposites. Corona aging studies have been carried out on unfilled silicone rubber, micro and nanocomposites for 25 h and 50 h of aging using a needle-plane electrode arrangement. Different parameters such as hydrophobicity, surface roughness, microcracks width on the aged surface, FTIR and SEM studies were carried out to study the corona aging resistance of the new and aged samples. The studies indicate that silicone rubber samples containing nanofillers at 3 wt % are able to impart significantly enough corona resistance compared to the unfilled and microcomposite samples. It is known that the discharge resistance offered by the fillers and the interaction/bonding between the fillers and polymers directly influences the corona aging resistance. Hence, the model proposed (discussed above) is valid for understanding the corona aging performance of the nanocomposites which is better than the unfilled and ATH filled silicone rubber. In addition to the tracking and erosion resistance and corona aging studies, multistress aging of commercially available polymeric insulators containing micron sized fillers has been carried out. The aging behaviour of the polymeric insulators under tropical and subtropical conditions (in the absence of discharges under wet conditions) has not been explored. Further, the long-term influence of the UV radiation on silicone rubber in the presence of temperature and electric stress is also not explored. Hence, to understand the aging phenomena (weathering characteristics) under multistress (electric, thermal and UV), distribution class composite polymeric insulators were aged for 30,000 h in a multistress aging chamber developed specifically for the studies. Insulators were continuously subjected to the accelerated electric and thermal stresses as well as UV radiation. Different studies like leakage current, SEM, hydrophobicity, surface roughness and low molecular weight (LMW) molecules content in the samples before and after the aging have been investigated. It is interesting to observe that even in the absence of electrical discharges on the surface of the material, significant monotonous reduction in LMW molecules has been observed w.r.t weathering time. Appreciable increase in the surface roughness (at least 200 % as that of the new material) as well as increased oxygen levels on the surface has also been observed. The results indicate that surface hydrophobicity is dynamic in nature and may not reflect the slow and permanent changes taking place in the bulk of the material. The results obtained for the nanocomposites enable us to design a better material with improved tracking, erosion and corona resistance without sacrificing the flexibility in the end product as well as ease of processing. The silicone rubber nanocomposites also open up the possibility for economically designing a smart material possibly with a higher reliability for outdoor insulator application.

Outdoor insulators are one of the most important parts of a power system. The reliability of a power system depends also on the reliability of the insulators. The main functions of an insulator used for outdoor applications are to give the necessary insulation, provide the necessary mechanical support to the transmission line conductor and also to resist the various environmental stresses like pollution, ultra violet rays etc. Traditionally porcelain and glass insulators have been used for outdoor insulator applications. They are good insulators under normal conditions and the cap and pin arrangement allows them to take up the mechanical load of the line. But owing to their large weight and brittle nature they are susceptible to vandalism and also they have increased cost of installation and commissioning. But the main problem of porcelain and glass insulators is its performance under polluted environmental condition. Under wet and polluted conditions, the porcelain insulators allow the formation of a conducting layer on the surface which results in setting up of leakage current, dry band arcing and power loss. This problem is further augmented under dc voltages where the stress is unidirectional and the contaminant deposition is higher as compared to ac. Polymeric insulators are a good alternative for porcelain and ceramic insulators for use especially under dc voltages because of their good pollution performance. The property of surface hydrophobicity resists the setting up of leakage currents and hence polymeric insulators help in reducing power loss. They are also light in weight and vandalism resistant and hence easier to install. But being polymeric, they form conductive tracks and erode when exposed to high temperatures which occur at the surface during dry band arcs and when exposed to corona discharges. The surface hydrophobicity is also temporarily lost when exposed to different electrical stresses. Silicone rubber is the most popular among the various choices of polymers for outdoor insulator applications. They have good surface hydrophobicity and tracking performance. But polymers in their pure form cannot be used as insulators because of their poor mechanical strength. Adding inorganic fillers into the polymer matrix not only improves its mechanical properties but also its erosion resistance. Micron sized Alumina Trihydrate (ATH) is used traditionally to improve the tracking and erosion resistance of polymeric insulators. A very high loading (up to 60%) is used. Adding such a high filler loading to the base polymer hampers its flexibility and the material processing. With the advent of nanotechnology, nano fillers have come into vogue. Studies conducted on nano filled polymers showed exciting results. A small amount of nano fillers in the polymer matrix showed significant improvement in the mechanical strength without hampering its flexibility. The electrical properties like tracking and erosion also improved with filler loading. Hence the use of nano filled silicone rubber is a good alternative for use as a high voltage insulator especially under dc voltages. Reports suggest that adding nano fillers into the silicone rubber matrix improves the tracking and erosion resistance and the corona degradation as compared to the unfilled samples under ac voltages. The literature on the dc performance of silicone rubber nano composites is scarce. So the present study aims to evaluate the performance of silicone rubber nano composites for tracking and erosion resistance and corona degradation under dc voltages. The tracking and erosion resistance under dc voltages was measured using the Inclined Plane Tracking and Erosion Resistance set up as per ASTM D2303 which was modified for dc voltage studies. The performance of nano Alumina and nano Silica fillers were evaluated under negative dc and the performance was compared with micron sized Alumina Trihydrate filled samples. The effect of filler loading was also studied. It was seen that the performance of the silicone rubber improved with filler loading. A small loading percentage of nano fillers were enough to give performance similar to silicone rubber filled with micron sized ATH filler. The silicone rubber performed better under negative dc as compared to ac and positive dc. The positive dc tests showed a migration of ions from the electrodes onto the sample surface. The increased surface conductivity resulted in very heavy erosion in the case of positive dc tested samples. The corona aging studies were also conducted on silicone rubber nano composites. Nano silica was used as filler in this case. Different filler loadings were employed to understand the effect of filler loading. The corona was generated using a needle plane electrode and samples were exposed to both positive and negative dc corona. The samples were exposed to corona for different time intervals – 25 and 50 hours to study the effect of exposure time. The hydrophobicity, crack width and surface roughness were measured after the tests. Adding nano fillers into the polymer matrix improved the corona performance. With filler loading, the performance improved. The samples exposed to positive dc corona performed better than those under negative dc corona. The loss of hydrophobicity, surface cracks and the surface roughness was less in the case of positive dc corona tested samples. With exposure time, the performance of silicone rubber became poorer for positive dc corona tested samples. For the negative dc corona tested samples, the performance seemed to improve with exposure time. The tracking and erosion resistance and the corona aging studies conducted showed that the performance of silicone rubber is improved by adding nano fillers into the polymer matrix. A small amount of nano filler loading was enough to perform similar to a heavily loaded micron filled sample. Hence nano fillers can be used as a good functional material to improve the performance of silicone rubber insulators especially under wet and polluted conditions.