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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.

Artículo de publicación ISIThe use of graphite and polyolefins as starting materials to prepare nanocomposites is convenient because both are inexpensive and have very different properties, one is conductive and the other is insulating. The formation of nanocomposites can extend the applicability of both commodities. In this work we synthesized nanocomposites of polyethylene (PE) with two types of graphites, graphite oxide (GO) and reduced graphite oxide (RGO), by in situ polymerization using a supported metallocene catalyst. The functional groups on the graphites were used to support the metallocene catalyst by a previous treatment with methylaluminoxane. The nanocomposites were obtained with good catalytic activities and presented excellent morphology and dispersion; their elastic modulus and crystallization temperatures were higher than those of neat PE. However, the nanocomposites PEGO were insulant, whereas PERGO had a conductivity of 1.1 x 10(-5) S cm(-1) with 3.1 wt% filler. This is a significant result compared to the conductivity obtained using non-supported graphite nanosheets where more than 15 wt% of graphite nanosheets are needed to obtain conductivities higher than 10(-7) S cm(-1). This improvement in the percolation threshold was attributed to the good morphology of the PERGO nanocomposites obtained due to the control of the graphitic sheets and the support methodology.CNPq 302902/2013-9 473128/2011-0 FAPERG-PRONEX 09/2009 Department of the Navy Grant N62909-11-1-7069 Millennium Nucleus of Chemical Processes and Catalysis (CPC) NC12008

Semi-conducting polyethylene (PE) nanocomposites with outstanding magnetic properties at room temperature were synthesized. These exceptional properties, for a diamagnetic and insulating matrix as PE, were obtained by polymerizing ethylene in the presence of a catalytic system formed by a metallocene catalyst supported on a mixture of reduced graphene oxide (rGO) and carbon nanotubes with encapsulated iron (CNT-Fe). It was used a constant and very low amount of CNT-Fe, obtained by vapor chemical deposition using ferrocene. The percolation threshold, to achieve conductivity, was obtained using a variable amount of rGO. The nanocomposites were semiconductors with the addition of 2.8 wt % and 6.0 wt % of the filler, with electrical conductivities of 4.99 3 10 26 S cm 21 and 7.29 3 10 24 S cm 21 , respectively. Very high coercivity values of 890-980 Oe at room temperature were achieved by the presence of only 0.04-0.06 wt % of iron in the nanocomposites. The novelty of this work is the production of a thermoplastic with both, magnetic and electric properties at room temperature, by the use of two fillers, that is rGO and CNT-Fe. The use of a small amount of CNT-Fe to produce the magnetic properties and variable amount of rGO to introduce the electrical conductivity in PE matrix let to balance both properties. The encapsulation strategy used to obtain Fe in CNT, protect Fe from easy oxidation and aggregation.

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Nanofillers of polyaniline nanofibers (PANI) with graphite oxide (GO) or reduced graphite oxide (rGO) were synthesized and characterized. Four samples of PANI/graphite with 10% and 30% of GO or rGO were obtained. The addition of GO or rGO in PANI nanofibers increased the conductivity and improved the thermal stability of the nanofillers. These nanofillers were used in the in situ ethylene polymerization producing PE/PANI/graphite nanocomposites characterized by SEM and TEM, revealing very particular morphologies. PANI/GO or PANI/rGO nanoparticles showed a good dispersion in polyethylene, and an increase in the thermal stability of the final material was observed. POLYM. COMPOS., 39:3645–3655, 2018. © 2017 Society of Plastics Engineers