Navegando por Palavras-chave "carbonization"
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- ItemSomente MetadadadosCarbon nanofibers obtained from electrospinning process(Iop Publishing Ltd, 2018) de Oliveira, Juliana Bovi; Guerrini, Lilia Mueller [UNIFESP]; Oishi, Silvia Sizuka; de Oliveira Hein, Luis Rogerio; Conejo, Luiza dos Santos; Rezende, Mirabel Cerqueira [UNIFESP]; Botelho, Edson CocchieriIn recent years, reinforcements consisting of carbon nanostructures, such as carbon nanotubes, fullerenes, graphenes, and carbon nanofibers have received significant attention due mainly to their chemical inertness and good mechanical, electrical and thermal properties. Since carbon nanofibers comprise a continuous reinforcing with high specific surface area, associated with the fact that they can be obtained at a low cost and in a large amount, they have shown to be advantageous compared to traditional carbon nanotubes. The main objective of this work is the processing of carbon nanofibers, using polyacrylonitrile (PAN) as a precursor, obtained by the electrospinning process via polymer solution, with subsequent use for airspace applications as reinforcement in polymer composites. In this work, firstly PAN nanofibers were produced by electrospinning with diameters in the range of (375 +/- 85) nm, using a dimethylformamide solution. Using a furnace, the PAN nanofiber was converted into carbon nanofiber. Morphologies and structures of PAN and carbon nanofibers were investigated by scanning electron microscopy, Raman Spectroscopy, thermogravimetric analyses and differential scanning calorimeter. The resulting residual weight after carbonization was approximately 38% in weight, with a diameters reduction of 50%, and the same showed a carbon yield of 25%. From the analysis of the crystalline structure of the carbonized material, it was found that the material presented a disordered structure.
- ItemSomente MetadadadosEstudo da conversão de lignina kraft em carvões(Universidade Federal de São Paulo (UNIFESP), 2016-08-29) Brazil, Tayra Rodrigues [UNIFESP]; Rezende, Mirabel Cerqueira Rezende [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Biomass is a renewable resource whose importance is growing every day, given the environmental and possible oil crisis concerns. Thus, the interest in optimizing its use is a current challenge. In this context, lignin is a prominent biomass, due to its wide availability in paper and pulp companies.This macromolecule is characterized by complex chemical structure, valuable physicochemical properties and varied chemical composition. The objective of this work is to select a Kraft lignin sample to be used as precursor material in coal production, by heat treatment (HTs) of carbonization, with posterior modification of the surface areas of obtained coals through chemical (acid attack) and physical (microwave plasma) processes. Determinations of moisture, carbon yield, ash and volatiles, and Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses were used to characterize two samples of Kraft lignins with different purities. The results show carbon yield values of ~26% and 44%, depending on the purity of lignin. FT-IR analyses show that the lignin samples are mainly composed by guaiacyl (G), and syringyl (S) units. Thermal analyses show residues of 30 and 36% by weight (under N2 up to 1000 °C) and glass transition temperatures ranging from 70 to 100 °C. SEM analyses show that the lignin more purity presents globular structures, typical of this material. From the correlation of the obtained results, the lignin more pure was chose to be carbonized. Longer HTs of lignin resulted in higher carbon yield (44% by weight) and favored the macroporosity decreasing and the nanopores population increasing. Raman spectroscopy and X-ray diffraction analyses show also that longer HTs improved the structural ordering of coals. The acid attack increased the surface area up to 40% (403 m2/g) in relation to the initial area (287 m2/g). Already the plasma treatments conferred the greatest surface area increases (up to 468 m2/g or up to 63%). From the results obtained is found that the production of activated carbon from lignin is feasible.
- ItemSomente MetadadadosStructural, morphological, and thermal characterization of kraft lignin and its charcoals obtained at different heating rates(Iop Publishing Ltd, 2018) Brazil, Tayra Rodrigues [UNIFESP]; Costa, Rogeria Nunes [UNIFESP]; Massi, Marcos [UNIFESP]; Rezende, Mirabel Cerqueira [UNIFESP]Biomass is a renewable resource that is becoming more import due to environmental concerns and possible oil crisis. Thus, optimizing its use is a current challenge for many researchers. Lignin, which is a macromolecule with complex chemical structure, valuable physicochemical properties, and varied chemical composition, is available in large quantities in pulp and paper companies. The objective of this work is the physicochemical characterization of two Kraft lignin samples with different purities, and the study of its thermal conversion into charcoal. The lignin characterization was based on chemical, TGA, DSC, FT-IR, particle sizes, and FEG-SEM analyses. These analyses show that the lignins are mainly composed of guaiacyl and syringyl units, with residues of 30-36 wt.%, in inert atmosphere, depending on the lignin purity. From these results, the more purified lignin with higher carbon yield (%C) was selected for charcoal production. The heat treatment (HT) for carbonization of lignin, at different times (90, 180, and 420 min), resulted in different %C (41-44 wt.%). Longer HT resulted in higher %C and in charcoals with smaller pore sizes. Nanopores (similar to 50 nm) are observed for the charcoal obtained with the longest HT.