In this study, we investigated the thermal, dynamic mechanical, mechanical, and electrical properties of polyethylene (PE)graphene nanosheet (GNS) nanocomposites, with GNS amounts from 0 to 20 wt %, prepared by in situ polymerization. The thermal stability was evaluated by thermogravimetric analysis (TGA) and showed that the addition of GNSs to the polyolefin matrix increased the onset degradation temperature by 30 C. The electrical conductivity, measured by the impedance technique, presented a critical percolation threshold of 3.8 vol % (8.4 wt %) of GNS. A slight decrease in the tensile strength was found. On the other hand, dynamic mechanical analysis showed an increase in the storage modulus of the nanocomposites compared with that of neat PE. The glass-transition temperature value increased from À111 C (neat PE) to À106 C (PE/6.6 wt % GNS). All of these results show that PE became stiffer and thermally more stable and could be transformed from an insulator to a semiconductor material in the presence of GNSs.

The synthesis of polyethylene/graphite nanocomposites by in situ polymerization was achieved using the catalytic system Cp2ZrCl2 (bis(cyclopentadienyl)zirconium(IV) dichloride)/methylaluminoxane (MAO). Graphite with nano dimensions, previously treated with MAO, was added into the reactor as filler at percentages of 1, 2, and 5% (w/w). XRD analysis showed that the chemical and thermal treatments employed preserve the structure of the graphite sheets. The formation of graphite nanosheets and nanocomposites was confirmed by TEM and AFM. TEM micrographics showed that the polyethylene grew between the graphene nanosheets, giving intercalated and exfoliated graphite nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 692–698, 2010

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.

The effect of alcaline and hot water surface treatments of piassava Attalea funifera fibers was investigated. The efficiency of each treatment was evaluated by Fourier transform infrared spectroscopy, X-ray diffractometry, optical microscopy, scanning electron microscopy and atomic force microscopy. The alkaline treatments were effective in removing the superficial lignin layer from the fiber, while the hot water treatment was not. Treatment with hot water and NaOH caused fiber defibrillation. NaOH was most effective in promoting both, a decrease in fiber diameter and an increase in fiber surface area. Treatment with Ca(OH) 2 led to the formation of a CaCO 3 layer deposited on the fiber, preventing defibrillation. The crystalline structure of the fiber was not altered by any of the treatments, maintaining type I cellulose.