Submitted by JOÃO VITOR PAULIN null (joaovp281@gmail.com) on 2016-04-12T18:10:04Z No. of bitstreams: 1 Paulin, JV - Dissertação.pdf: 8544821 bytes, checksum: 8c1f65d0bedc5cc3413277b0fdc03393 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-13T17:18:23Z (GMT) No. of bitstreams: 1 paulin_jv_me_bauru.pdf: 8544821 bytes, checksum: 8c1f65d0bedc5cc3413277b0fdc03393 (MD5) / Made available in DSpace on 2016-04-13T17:18:23Z (GMT). No. of bitstreams: 1 paulin_jv_me_bauru.pdf: 8544821 bytes, checksum: 8c1f65d0bedc5cc3413277b0fdc03393 (MD5) Previous issue date: 2016-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Por mais de 40 anos, a melanina tem despertado cada vez mais atenção como um material funcional para dispositivos orgânicos como células solares, transistores, sensores, engenharia de tecidos, baterias, dispositivos de memória e drug delivery. As melaninas apresentam uma combinação de propriedades físico-químicas únicas com sua biocompatibilidade intrínseca que inspira seu uso em aplicações bioeletrônicas. Contudo, sua aplicação em dispositivos orgânicos é limitada devido a sua baixa solubilidade na maioria dos solventes. Assim, neste trabalho, buscamos obter derivados solúveis de melanina a partir de uma abordagem sintética alternativa utilizando diferentes pressões (4 a 8 atm) oxigênio molecular como agente oxidante em água ou DMSO. Espectroscopia UV-Vis, FTIR, RMN e XPS foram utilizados para caracterização, tendo como referência os materiais obtidos a partir das rotas sintéticas tradicionais. A utilização de pressão de oxigênio acelerou o processo sintético em ambos os casos e foi possível obter uma alta proporção DHICA/DHI. A principal diferença é a obtenção em meio aquoso de um material solúvel em água sem nenhuma funcionalização exótica, enquanto que em solvente orgânico o derivado da melanina, funcionalizado com grupos sulfonatos, apresenta solubilidade em DMSO, DMF e N-metil-2-pirrolidona. Um mecanismo reacional baseado na elevada natureza oxidante do meio sintético, incluindo na decomposição do H2O2 pelo oxigênio é proposto para explicar as alterações estruturais observadas. / For over 40 years, melanin has been focus of increasing attention as a promising functional material for organic devices like solar cells, transistors, sensors, tissue engineering, charge storage, memory devices and drug delivery. Melanins present a combination of unique physical-chemical properties with its intrinsic biocompatibility inspire its use in bioelectronics applications. However, their applicability in organic devices is limited due to its low solubility in most solvents. Thus, in this work, we aim to achieve soluble derivatives of melanin from an alternative synthetic approach using different oxygen pressures (4 to 8 atm) as an oxidizing agent in water or DMSO. UV-Vis spectroscopy, FTIR, RMN and XPS was used to characterize the material using conventional synthesized melanin as a reference. The use of oxygen pressure accelerated the synthetic process and in both cases it was possible to obtain a high DHICA/DHI ratio. The main difference is obtained in aqueous medium a water soluble material without any exotic functionalization, while in organic solvent we have a functionalization with sulfonate group with solubility in DMSO, DMF and N-methyl-2-pyrrolidone. A reaction mechanism based on the higher oxidative nature of the reaction medium including oxygen-induced decomposition of H2O2 is proposed to explain the structural changes observed.

Recent developments have indicated high oxygen consumption rates of about 35 g-mole/m³-min during oxidative pressure leaching. At such high oxygen consumption rates the mass transfer of dissolved oxygen at the gas-liquid interface may become rate-limiting. The objective of this study was to obtain an understanding of the gas-liquid mass transfer processes that take place in mechanically agitated pressure leaching systems. The classical reaction between sodium sulphite and dissolved oxygen to form sulphate at atmospheric pressure was used to determine the oxygen mass transfer rates in a 200-liter asymmetrical plastic tank, modelled after the shape of the first compartment of the zinc pressure leach. The effect of this asymmetry was compared with the work of Swiniarski who used a cylindrical symmetrical tank of similar volume. A number of process variables such as the impeller type and size, the impeller speed, the impeller immersion depth and the effect of full baffles that affect mixing were investigated. Also, the volumetric power consumption associated with the mass transfer rates were measured. The results indicate that the asymmetrical tank is at least 3.6 times more efficient in mass transfer than the symmetrical tank. There is a critical speed below which the mass transfer parameter, K[formula omitted], is almost zero and above which K[formula omitted] increases almost linearly with impeller tip speed. A simple energy balance model for bubble creation can predict the critical tip speed. It is shown that K[formula omitted] is enhanced at shallow depths, with a corresponding high mass transfer to energy ratio. The relative effectiveness of impeller types and sizes with regard to the use of power for gas-liquid mass transfer was established. Full baffles degrade the mass transfer rate at increased depth of impeller immersion. The results also add substantial support to the findings provided by DeGraaf [5] that: (i) The dimensionless correlations used in liquid mixing systems do not accurately predict dispersion rates by agitators. (ii) The optimum conditions for gas dispersion and the consequent generation of gas-liquid interfacial area are different from fluid mixing. (iii) The classical mixing power equations for impellers markedly overestimate power requirements during impeller gas dispersion. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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