Obtenção e caracterização de nanofibras de carbono a partir de PAN/lignina processadas por eletrofiação
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Data
2022-09-16
Autores
Cintra, Isabela Luiza Rodrigues
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Universidade Estadual Paulista (Unesp)
Resumo
As fibras de carbono têm grande aplicação em diversos segmentos industriais, destacando-se o aeroespacial e o automobilístico. Atualmente, o precursor mais utilizado na obtenção das fibras de carbono é a poliacrilonitrila (PAN) devido ao elevado teor de carbono fixo. No entanto, a PAN é um polímero caro e de origem do petróleo. Precursores oriundos de fontes renováveis tem sido estudados, tais como a lignina Kraft (LK) que é uma macromolécula gerada como resíduo pela indústria de papel e possui em sua composição elevado teor de carbono. Desta forma, blendas de PAN/lignina têm sido muito estudadas para obtenção de fibras de carbono. No entanto, durante o processo de obtenção destas fibras, uma das etapas mais complexas é a estabilização térmica oxidativa. Esta etapa é importante para manter a geometria da fibra durante todo o restante do processo de carbonização, além de tornar as fibras infusíveis. Neste contexto, o objetivo deste trabalho foi obter mantas de carbono utilizando como precursores fibras de PAN/LK, obtidas por eletrofiação, visando um estudo sistemático em relação à etapa de estabili-zação térmica oxidativa. Inicialmente, foram processadas via eletrofiação blendas com diferentes proporções de PAN/LK (90/10 % m/m; 80/20 % m/m; 70/30% m/m; 60/40% m/m e 50/50% m/m) sendo estas caracterizadas quanto à estrutura química por espectroscopia de infraverme-lho com transformada de Fourier (FT-IR), a morfologia por microscopia eletrônica de varredura (MEV) e por análises térmicas (calorimetria exploratória diferencial, DSC, e termogravimetria, TGA). Os parâmetros de estabilização térmica oxidativa foram definidos baseando-se em um planejamento fatorial 23. As amostras foram analisadas por FT-IR e DSC e o índice de cicliza-ção foi obtido a partir dessas duas técnicas. A partir dos resultados obtidos foram selecionados os melhores parâmetros para estabilização térmica oxidativa das mantas eletrofiadas e, posteri-ormente, estabelecidos os parâmetros de carbonização mais adequados para a obtenção de man-tas de carbono. As mantas carbonizadas foram caracterizadas em relação à condutividade elétri-ca (espectroscopia de impedância), estrutura química (espectroscopia Raman e FT-IR), estrutura cristalina (DRX) e morfologia (MEV). As mantas carbonizadas apresentaram pouco rendimen-to de material após o processo de carbonização e a diminuição de aproximadamente 70% no diâmetro das fibras. Por meio das análises estruturais (DRX e RAMAN) foi verificado que entre as amostras produzidas a cristalinidade variou de 45% a 57%, e uma estrutura pouco ordenada, indicado pela razão ID/IG que variou de 2,56 a 3,14 para estas amostras.
Carbon fibers have great application in several industrial segments, especially aerospace and automotives. Currently, the most used precursor to obtaining carbon fibers is polyacrylonitrile (PAN) due to the advantage of obtaining at least twice as much fixed carbon. However, PAN is an expensive, petroleum-based polymer. Precursors from renewable sources have been studied, such as Kraft lignin (KL) which is a macromolecule generated as waste by the paper industry and has high carbon content in its composition. Thus, PAN/lignin blends have been extensively studied to obtain carbon fibers. However, during the process of obtaining these fibers, one of the most complex steps is oxidative thermal stabilization. It is at this stage that the increase in the density of the fibers occurs and it is important to maintain the fiber geometry throughout the rest of the carbonization process, in addition to making the fibers infusible. In this context, the objective of this work was to obtain carbon blankets using fibers of PAN/LK blends as precursors, obtained by electrospinning, aiming at a systematic study of the oxidative thermal stabilization step. Initially, blends with different proportions of PAN/LK (90/10 % w/w; 80/20 % w/w; 70/30% w/w; 60/40% w/w e 50/50% w/w % w/w) were processed via electrospinning, which was characterized in terms of chemical structure by Fourier transform infrared spectroscopy (FT-IR), morphology by scanning electron microscopy (SEM) and by thermal analysis (differential scanning calorimetry, DSC, and thermogravimetry, TGA). The oxidative thermal stabilization parameters were defined based on a 23 factorial design. The samples, after oxidative thermal stabilization, were analyzed by FT-IR and DSC and the cyclization index was obtained from these two techniques. From the results obtained, the best parameters for oxidative thermal stabilization of the electrospun blankets were selected and, later, the most adequate carbonization parameters were established to obtain carbon blankets. The carbonized blankets were characterized in terms of electrical conductivity (impedance spectroscopy), chemical structure (Raman and FT-IR spectroscopy), crystal structure (XRD), and morphology (SEM). The carbonized blankets showed little material yield after the carbonization process and a decrease of approximately 70% in the fiber diameter. Through structural analyzes (XRD and RAMAN) it was verified that the material has a crystallinity of 45% (E3, E4, and E8) and 57% (E7) and a poorly ordered structure, indicated by the ID/GI ratio.
Carbon fibers have great application in several industrial segments, especially aerospace and automotives. Currently, the most used precursor to obtaining carbon fibers is polyacrylonitrile (PAN) due to the advantage of obtaining at least twice as much fixed carbon. However, PAN is an expensive, petroleum-based polymer. Precursors from renewable sources have been studied, such as Kraft lignin (KL) which is a macromolecule generated as waste by the paper industry and has high carbon content in its composition. Thus, PAN/lignin blends have been extensively studied to obtain carbon fibers. However, during the process of obtaining these fibers, one of the most complex steps is oxidative thermal stabilization. It is at this stage that the increase in the density of the fibers occurs and it is important to maintain the fiber geometry throughout the rest of the carbonization process, in addition to making the fibers infusible. In this context, the objective of this work was to obtain carbon blankets using fibers of PAN/LK blends as precursors, obtained by electrospinning, aiming at a systematic study of the oxidative thermal stabilization step. Initially, blends with different proportions of PAN/LK (90/10 % w/w; 80/20 % w/w; 70/30% w/w; 60/40% w/w e 50/50% w/w % w/w) were processed via electrospinning, which was characterized in terms of chemical structure by Fourier transform infrared spectroscopy (FT-IR), morphology by scanning electron microscopy (SEM) and by thermal analysis (differential scanning calorimetry, DSC, and thermogravimetry, TGA). The oxidative thermal stabilization parameters were defined based on a 23 factorial design. The samples, after oxidative thermal stabilization, were analyzed by FT-IR and DSC and the cyclization index was obtained from these two techniques. From the results obtained, the best parameters for oxidative thermal stabilization of the electrospun blankets were selected and, later, the most adequate carbonization parameters were established to obtain carbon blankets. The carbonized blankets were characterized in terms of electrical conductivity (impedance spectroscopy), chemical structure (Raman and FT-IR spectroscopy), crystal structure (XRD), and morphology (SEM). The carbonized blankets showed little material yield after the carbonization process and a decrease of approximately 70% in the fiber diameter. Through structural analyzes (XRD and RAMAN) it was verified that the material has a crystallinity of 45% (E3, E4, and E8) and 57% (E7) and a poorly ordered structure, indicated by the ID/GI ratio.
Descrição
Palavras-chave
Poliacrilonitrila, Lignina, Eletrofiação, Estabilização Térmica Oxidativa, Carbonização, Carbon nanofibers, Polyacrylonitrile, Lignin, Electrospinning, Carbonization, Carbonização, Compósitos poliméricos