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.
In this work, the synthesis of polypropylene (PP)/graphene nanosheet (GNS) nanocomposites by in situ polymerization using metallocene catalysts was studied. Initial reactions were performed using rac‐Et(Ind)2ZrCl2 and rac‐Me2Si(Ind)2ZrCl2 catalysts to select the best one to obtain good molecular weight, thermal properties, and tacticity. Subsequently, PP nanocomposites with different loadings of GNS were obtained. GNS from two different sources [Graphite Nacional (GN) and Graphite Aldrich (GA)] have been used, and the differences between the obtained nanocomposites were evaluated. The GNS and nanocomposites were studied by scanning electronic microcopy, transmission electronic microcopy, and X‐ray diffraction. They showed that the GN nanosheets had lower crystal size and diameter than the GA nanosheets and dispersed better in the PP matrix. Differential scanning calorimetry analyses of both types of nanocomposites showed an increase in the crystallization temperature with increasing graphite loading. The polymeric materials were also characterized by GPC, thermogravimetric analysis, and 13C NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
The difficult processability of polyaniline (PAni) can be overcome by preparing composites with high density polyethylene (HDPE), resulting in a conducting material with improved mechanical properties. PAni nanofibers were synthesized in this research using a rapid mixing method, while HDPE/PAni composites were prepared by in situ polymerization using Cp 2 ZrCl 2 /MAO as a catalyst system. Different experimental conditions for polymerization and an electrochemical study were performed. The findings confirmed that the addition of small amounts of Pani (up to 7%) and longer impregnation (120 min) with methylaluminoxane (MAO) before polymerization are important factors contributing to increased catalytic activity. Analysis by cyclic and differential pulse voltammetry indicates that MAO reacts with the PAni in the ethylene polymerization process, and forms active species in the presence of the catalyst. Changes in catalytic activity may be due to the kinetic consumption of the active species, which become less important in the presence of PAni.
In this work electro‐conductive polyaniline nanofibers (PAni‐nanofibers) were prepared via interfacial methodology. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that the synthesized PAni‐nanofibers present high aspect ratio with an average diameter of 80 nm, while they exhibit high conductivity (DC conductivity values: 4.19 ± 0.21 S cm−1). After specific treatment to remove moisture and remaining trapped HCl from PAni‐nanofibers, it was possible to prepare promising polyethylene (PE)/PAni composites by in situ polymerization of ethylene using bis(cyclopentadienyl) zirconium(IV) dichloride (Cp2ZrCl2) and methylaluminoxane (MAO) as catalytic system. More precisely, various contents of PAni‐nanofibers (from 0.2 to 7 wt %) were successfully incorporated in the in situ produced PE/PAni nanocomposites. PAni‐nanofibers were found to affect significantly the crystallization of the polyolefinic matrix while preserving its thermal stability. Preliminary measurements of electric properties showed PAni‐nanofibres are able to bring electro‐conductive properties to the in situ polymerized PE/PAni composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41197.
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