Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Few Layer Reduced Graphene Oxide: Evaluation of the Best Experimental Conditions for Easy Production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Síntese e propriedades de nanocompósitos de polietileno/nanolâminas de grafeno obtidos através de polimerização in situ

A síntese de nanocompósitos de polietileno/nanolâminas de grafeno através de polimerização in situ foi alcançada utilizando o sistema catalítico Cp2ZrCl2/MAO (dicloro bis(ciclopentadienil)zircônioIV)/metilaluminoxano(MAO). Grafite com dimensões nanométricas, previamente tratada com MAO foi adicionada no reator como carga em percentuais que variaram de 1,2 até 20,9% (p/p). A análise de difração de raios-X (DRX) mostrou que os tratamentos térmico e físico empregados preservaram a estrutura das lâminas de grafite. A formação de nanolâminas de grafeno (NG) e dos nanocompósitos foi confirmada por microscopia eletrônica de transmissão (MET) e microscopia de força atômica (AFM). As micrografias de MET mostraram que o polietileno cresce entre as NG, resultando em nanocompósitos intercalados e esfoliados. As propriedades térmicas, dinâmico-mecânicas, mecânicas e elétricas foram investigadas por análise termogravimétrica (TGA), análise dinâmico-mecânica (DMA), resistência à tração e espectroscopia de impedância eletroquímica (EIE), respectivamente. As NG aumentaram a estabilidade térmica do polietileno em 30 °C. Uma leve diminuição na resistência à tração foi verificada com a adição das NG à matriz polimérica. A adição de grafite ao polietileno aumentou o módulo de armazenamento, assim como o valor da temperatura de transição vítrea. A condutividade elétrica apresentou um limite de percolação de 3,8% vol. (8,4% p/p) de NG. Todos os resultados mostraram que o polietileno tornou-se mais rígido e termicamente mais estável e passou de um material isolante para semicondutor na presença das nanolâminas de grafeno. Com o objetivo de estudar outros caminhos para obter grafeno foi estudada a síntese de óxido de grafite (GO) que foi realizada através do protocolo de Staudenmaier. O grafite oxidado foi reduzido nas temperaturas de 600, 700 e 1000 °C. A melhor temperatura de redução foi de 700 °C, pois nessa temperatura a análise de espectroscopia Raman mostrou a presença de grafenos.The synthesis of polyethylene/graphene nanosheet (PE/GNS) nanocomposites by in situ polymerization was achieved using the catalytic system Cp2ZrCl2/MAO (bis(cyclopentadienyl)zirconium(IV) dichloride)/methylaluminoxane(MAO). Graphite with nano dimensions (GNS), previously treated with MAO, was added into the reactor as filler at percentages from 1.2 to 20.9% (w/w). X-ray diffraction analysis (XRD) showed that the chemical and thermal treatments employed preserved the structure of the graphite sheets. The formation of graphene nanosheets and nanocomposites was confirmed by TEM and AFM. TEM micrographs showed that the polyethylene grew between the graphene nanosheets, giving intercalated and exfoliated graphite nanocomposites. The thermal, dynamic mechanical, mechanical and electrical properties were investigated by thermogravimetric analysis (TGA), dynamic-mechanical analysis (DMA), tensile strength and electrochemical impedance spectroscopy (EIS), respectively. The GNS increased the thermal stability of polyethylene in 30 °C. A slight decrease in tensile strength was observed with the addition of GNS to the polymer matrix. The addition of graphite to the polyethylene increased the storage modulus, as well as the glass transition temperature. The electrical conductivity showed a percolation threshold of 3.8 vol%. (8.4% w/w) of GNS. All results showed that the polyethylene became stiffer and thermally more stable and it could be transformed from an insulator to a conductor material in the presence of GNS. In order to study other path to obtain graphene, the synthesis of graphite oxide (GO) was performed using the Staudenmaier protocol. The oxidized graphite was reduced at temperatures of 600, 700 and 1000 °C. The best reduction temperature was 700 ° C because Raman spectroscopy analysis showed the presence of graphene

Síntese e propriedades de nanocompósitos de polietileno/nanolâminas de grafeno obtidos através de polimerização in situ

A síntese de nanocompósitos de polietileno/nanolâminas de grafeno através de polimerização in situ foi alcançada utilizando o sistema catalítico Cp2ZrCl2/MAO (dicloro bis(ciclopentadienil)zircônioIV)/metilaluminoxano(MAO). Grafite com dimensões nanométricas, previamente tratada com MAO foi adicionada no reator como carga em percentuais que variaram de 1,2 até 20,9% (p/p). A análise de difração de raios-X (DRX) mostrou que os tratamentos térmico e físico empregados preservaram a estrutura das lâminas de grafite. A formação de nanolâminas de grafeno (NG) e dos nanocompósitos foi confirmada por microscopia eletrônica de transmissão (MET) e microscopia de força atômica (AFM). As micrografias de MET mostraram que o polietileno cresce entre as NG, resultando em nanocompósitos intercalados e esfoliados. As propriedades térmicas, dinâmico-mecânicas, mecânicas e elétricas foram investigadas por análise termogravimétrica (TGA), análise dinâmico-mecânica (DMA), resistência à tração e espectroscopia de impedância eletroquímica (EIE), respectivamente. As NG aumentaram a estabilidade térmica do polietileno em 30 °C. Uma leve diminuição na resistência à tração foi verificada com a adição das NG à matriz polimérica. A adição de grafite ao polietileno aumentou o módulo de armazenamento, assim como o valor da temperatura de transição vítrea. A condutividade elétrica apresentou um limite de percolação de 3,8% vol. (8,4% p/p) de NG. Todos os resultados mostraram que o polietileno tornou-se mais rígido e termicamente mais estável e passou de um material isolante para semicondutor na presença das nanolâminas de grafeno. Com o objetivo de estudar outros caminhos para obter grafeno foi estudada a síntese de óxido de grafite (GO) que foi realizada através do protocolo de Staudenmaier. O grafite oxidado foi reduzido nas temperaturas de 600, 700 e 1000 °C. A melhor temperatura de redução foi de 700 °C, pois nessa temperatura a análise de espectroscopia Raman mostrou a presença de grafenos.The synthesis of polyethylene/graphene nanosheet (PE/GNS) nanocomposites by in situ polymerization was achieved using the catalytic system Cp2ZrCl2/MAO (bis(cyclopentadienyl)zirconium(IV) dichloride)/methylaluminoxane(MAO). Graphite with nano dimensions (GNS), previously treated with MAO, was added into the reactor as filler at percentages from 1.2 to 20.9% (w/w). X-ray diffraction analysis (XRD) showed that the chemical and thermal treatments employed preserved the structure of the graphite sheets. The formation of graphene nanosheets and nanocomposites was confirmed by TEM and AFM. TEM micrographs showed that the polyethylene grew between the graphene nanosheets, giving intercalated and exfoliated graphite nanocomposites. The thermal, dynamic mechanical, mechanical and electrical properties were investigated by thermogravimetric analysis (TGA), dynamic-mechanical analysis (DMA), tensile strength and electrochemical impedance spectroscopy (EIS), respectively. The GNS increased the thermal stability of polyethylene in 30 °C. A slight decrease in tensile strength was observed with the addition of GNS to the polymer matrix. The addition of graphite to the polyethylene increased the storage modulus, as well as the glass transition temperature. The electrical conductivity showed a percolation threshold of 3.8 vol%. (8.4% w/w) of GNS. All results showed that the polyethylene became stiffer and thermally more stable and it could be transformed from an insulator to a conductor material in the presence of GNS. In order to study other path to obtain graphene, the synthesis of graphite oxide (GO) was performed using the Staudenmaier protocol. The oxidized graphite was reduced at temperatures of 600, 700 and 1000 °C. The best reduction temperature was 700 ° C because Raman spectroscopy analysis showed the presence of graphene

Novo catalisador de zircônio para polimerização de olefinas

No presente trabalho o novo complexo diclorobis(2-etil-3-hidroxi-4- pirona)zircônio(IV) (II) foi sintetizado e o seu desempenho na polimerização de etileno foi comparado com o complexo diclorobis(3-hidroxi-2-metil-4-pirona)Zr(IV) (I). O complexo (II), que é um ligante alcóxido bidentado com dois átomos doadores de oxigênio, foi sintetizado através de três diferentes rotas sintéticas. Entretanto, a melhor atividade catalítica foi alcançada quando o complexo foi sintetizado utilizando o aduto de zircônio em THF. O complexo foi caracterizado por RMN de 13C, de 1H, HETCOR, análise elementar e UV-Vis. Os estudos de RMN mostraram a existência de quatro isômeros para o complexo. Estudos eletroquímicos dos complexos [ZrCl2(pirona)2] (metil ou etil) foram realizados com o objetivo de entender se a natureza do grupo alquil poderia influenciar a densidade eletrônica do Zr(IV). Foi observado que não há influência, porque os valores de potenciais de redução que envolve o centro metálico são semelhantes para os dois complexos. O complexo se mostrou ativo na polimerização de etileno usando MAO como cocatalisador, produzindo polietileno de alta densidade com alto peso molecular e estreita polidispersão. Comparando com o complexo (I), o complexo (II) foi mais ativo. As análises eletroquímicas indicam que ambos os complexos de zircônio têm a necessidade da coordenação de etileno para estabilizar a espécie ativa de zircônio gerada pela adição de MAO.In the present work the new complex dichlorobis(2-ethyl-3-hydroxy-4- pyrone)zirconium(IV) (II) was synthesized and its performance at ethylene polymerization was compared with the complex (3-hydroxy-2-methyl-4-pyrone)zirconium(IV) (I). Complex (II), that is a bidentade alkoxide ligand with two oxygen donor atoms, was synthesized by three different ways. However, the best catalytic activity was reached when the complex was synthesized using the zirconium adduct. The complex was characterized by 13C NMR, 1H NMR, HETCOR, elementary analysis and UV-Vis. The NMR studies showed the existence of four isomers. With the objective to understand if the nature of the alkyl group could influence the electronic density of Zr(IV), electrochemical studies of complexes [ZrCl2(pyrone)2] (methyl or ethyl) were done. It was observed that there is no influence, because the values of reduction potentials attributed to the metallic center are similar for the two complexes. The complex was catalytic active at ethylene polymerization using MAO as cocatalyst. It was produced high-density polyethylene with high molecular weight and narrow polydispersity. Comparing with the complex (I), the complex (II) was more active. Electrochemical analyses indicated that both zirconium complexes need to coordinate with ethylene to stabilize the active species of zirconium generated by MAO addition

Comparação entre nanocompósitos de polietileno/nanotubos de carbono e polietileno/nanolâminas de grafeno obtidos por polimerização in situ

Nanocompósitos de polietileno/nanotubos de carbono foram sintetizados através da polimerização in situ para serem comparados com nanocompósitos de polietileno/nanolâminas de grafeno, obtidos nas mesmas condições. Os nanocompósitos de polietileno/NTC foram obtidos com boas atividades catalíticas e foram caracterizados por DSC e MET. Os nanocompósitos com NG apresentaram melhor estabilidade térmica que os de NTC, porem não houve diferenças significativas nas propriedades dinâmico-mecânicas. No estudo da condutividade elétrica os nanocompósitos PE/NTC atingiram condutividades de materiais semicondutores com menor teor de nanocarga que os de PE/NG

Comparison between polyethylene/carbon nanotubes and polyethylene/graphene nanosheets nanocomposites obtained by in situ polymerization

Nanocompósitos de polietileno/nanotubos de carbono foram sintetizados através da polimerização in situ para serem comparados com nanocompósitos de polietileno/nanolâminas de grafeno, obtidos nas mesmas condições. Os nanocompósitos de polietileno/NTC foram obtidos com boas atividades catalíticas e foram caracterizados por DSC e MET. Os nanocompósitos com NG apresentaram melhor estabilidade térmica que os de NTC, porem não houve diferenças significativas nas propriedades dinâmico-mecânicas. No estudo da condutividade elétrica os nanocompósitos PE/NTC atingiram condutividades de materiais semicondutores com menor teor de nanocarga que os de PE/NG.Polyethylene/carbon nanotubes, PE/NTC, nanocomposites were synthesized by in situ polymerization for comparison with polyethylene/graphene nanosheets, PE/NG, nanocomposites obtained in the same conditions. The nanocomposites of polyethylene/NTC were obtained with good catalytic activities and were characterized by DSC and TEM. The nanocomposites with NG showed better thermal stability than with NTC, however, no significant differences in dynamic mechanical properties were found. In the electrical conductivity study, PE/NTC nanocomposites reached conductivities of semiconductor materials at lower content of filler than PE/NG nanocomposites

Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere