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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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abstract: Natural rubber and rubber products can be produced from the guayule plant (Parthenium argentatum Gray), which is a low input perennial shrub native to Mexico and the American Southwest. Guayule rubber has the potential to replace Hevea (Hevea brasiliensis) rubber, the most common natural rubber, and synthetic rubber, which is derived from petroleum, in a wide variety of products, including automobile tires. Rubbers make up approximately 47% of the analyzed conventional passenger tire's weight, with 31% from synthetic rubber and 16% from natural Hevea rubber. Replacing the current rubber sources used for the tire industry with guayule rubber could help reduce dependency on imported rubber in addition to reducing greenhouse gas emissions. Moreover, residues from guayule rubber are being researched as a bioenergy feedstock to further improve the environmental footprint of guayule rubber products. This study used life cycle assessment (LCA), a useful tool to determine environmental impacts from a product or process, to quantify and compare environmental impacts of the raw material extraction, transportation and manufacturing of a conventional and a guayule rubber based passenger tire. The impact results of this comparative LCA identified the major environmental impacts and contributing process and informed how the impacts from the tire production can be reduced through utilization of natural rubber co-products as electricity off-sets and reducing guayule rubber's environmental impacts through agricultural and transportation modifications. Results showed that tire raw material extraction contributed the majority of impacts in all categories, where the production of guayule rubber for guayule tires, and the production of synthetic rubber for conventional tires, were the main contributors. Guayule rubber impacts occurred mainly from electricity consumption for agricultural irrigation, while synthetic rubber is a petroleum-based material resulting in high impacts. Transportation impacts had little significance compared to other stages in the life cycle, except for smog impacts, which occurred mainly from truck transport for guayule tires, and transoceanic transport for conventional tires. Tire manufacturing impacts occurred mainly from electricity use in the facilities and were reduced with the use of guayule rubber in guayule tires. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2014

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Le caoutchouc naturel (CN), un produit dérivé du latex d'Hevea brasiliensis, est connu pour ses propriétés mécaniques supérieures pour certaines à celles de ses concurrents synthétiques. Néanmoins, le haut degré d'insaturation du poly(cis-1,4-isoprene) le rend susceptible à la thermo-oxydation. Heureusement, le CN est doté de composés non-isoprènes dont certains ont des propriétés antioxydantes. Les lipides sont les plus importants non-isoprènes retenus dans le caoutchouc et contiennent des molécules à activité antioxydante en particulier les tocotriènols. Il est connu que durant la maturation de coagula de latex, la composition chimique et les propriétés du caoutchouc obtenu sont altérées, mais les mécanismes complexes de cette altération ne sont pas encore complètement élucidés. Dans cette étude, l'évolution de certaines molécules antioxydantes natives pendant la maturation a été suivie en relation avec certaines propriétés physiques du caoutchouc. Deux expérimentations de maturation ont été mises en œuvre. La première mettait en jeu des conditions non contrôlées de maturation suivies d'un procédé de confection du caoutchouc basé sur celui des feuilles fumées (RSS) ou non (USS). La seconde a été conduite dans un dispositif expérimental dédié permettant le contrôle des facteurs de l'environnement tels que l'humidité relative, la température et la concentration en oxygène. Le procédé de confection du caoutchouc était dans ce cas basé sur celui des caoutchoucs spécifiés techniquement (TSR). L'évolution des échantillons pendant la maturation a été étudiée à différentes échelles : propriétés en masse (P0, P30 et PRI), mésostructure (% gel, Mw and Mn) et composition biochimique (lipides). En parallèle, l'activité antioxydante in vitro des extraits lipidiques correspondants a été mesurée en utilisant une méthode DPPH optimisée. La quantité et la qualité des lipides extraits évoluent pendant la maturation, en particulier en aérobiose. La quantité totale de lipides décroit, avec, en début de maturation, une libération d'acides gras dont la quantité diminue ensuite, avec une disparation des espèces insaturées en premier. La quantité de γ-tocotrienol libres extraits change peu au cours de la maturation alors que sa forme estérifiée montre un enrichissement en acides gras saturés. L'activité antioxydante de l'extrait lipidique mesurée in vitro est corrélée avec la concentration de γ-tocotrienol libre mais pas avec les valeurs de P30 et PRI qui estiment la résistance du caoutchouc à la thermo-oxydation. Cette absence de corrélation pourrait être due à la différence des conditions de mesure in-vitro de celles existantes au sein du matériau caoutchouc. La localisation des antioxydants dans le caoutchouc et en particulier leur possibilité physique d'interagir avec les doubles liaisons du poly(cis-1,4-isoprene) ou avec des espèces oxydantes reste à étudier afin de comprendre ce qui régit la chute de P30 au cours de la maturation. Des lipides non extractibles ou des molécules non-isoprènes plus polaires (protéines, polyphénols, …) pourraient également influencer la résistance du caoutchouc à la thermo-oxydation. / Natural rubber (NR), a derived product from H. brasiliensis latex, is known for its high mechanical properties that are, for some, superior to those of its synthetic counterparts. However, the high degree of unsaturation of poly(cis-1,4-isoprene) makes it susceptible to thermo-oxidation. Fortunately, NR is endowed with non-isoprene components of which some have antioxidant properties. Especially, lipids, the main non-isoprene component retained in NR, have been reported to contain antioxidant substances, especially tocotrienols. It is well known that during the maturation of latex coagula, both NR physical properties and chemical composition are altered, but the complex mechanisms of this alteration are still to be elucidated. In the present work, the evolution of some native antioxidant molecules during maturation was followed in relation with some physical properties. Two experimental conditions of maturation were chosen. The first experiment involved uncontrolled conditions based on traditional unsmoked (USS) or ribbed smoked sheet (RSS) processing, while the second was performed in a dedicated maturation device with full control of environmental factors (relative humidity, temperature and oxygen content) followed by a processing based on that of Technically Specified Rubber (TSR). The evolution of samples during maturation was studied at different scales: bulk properties (P0, P30 and PRI), mesostructure (% gel content, Mw and Mn) and biochemical composition (lipids components). In parallel, in vitro antioxidant activity of NR lipid extracts was also investigated using an optimized DPPH method. Lipid quantity and quality evolved during maturation, especially under aerobic conditions. The total amount of lipid extract decreased, with a release of free fatty acids at early stage of maturation followed by a later decrease, unsaturated fatty acids being the first to disappear. The amount of extractable free γ-tocotrienol did not change much during maturation, while its esterified form was enriched in saturated fatty acids. The antioxidant activity measured in vitro correlated well with free γ-tocotrienol concentration but not with the resistance of rubber to thermo-oxidation assessed by P30 or PRI. Indeed, the in vitro conditions of measurement were far from those occurring inside rubber material. The localization of antioxidants in rubber and especially their physical possibility to interact with the double bonds of poly(cis-1,4-isoprene) or with oxidant species should be further investigated to understand what drives the drop of P30 along maturation time. Non extractable lipids or more polar non-isoprene molecular species (proteins, polyphenols, etc…) could also influence the resistance to thermo-oxidation.