Polypropylene/graphite nanocomposites by thermo-kinetic mixing

Polypropylene (PP)/graphite nanocomposites have been prepared by melt-mixing PP with different levels of graphite (G) and graphite oxide (GO) using maleated PP(PPg-MA) and graphite oxide (GO) as interface modifiers. Melt-mixing was achieved using a Gelimat, a high-speed thermo-kinetic mixer. The Gelimat system is specifically designed to handle difficult compounding and dispersion applications by completely mixing, heating and compounding products within a few minutes. Therefore, the thermal history of the compounded polymer is very short, which limits degradation. Interfacial modification by addition of maleated PP and graphite oxide is essential for producing PP/G nanocomposite. The graphite oxide then interacts with the maleic anhydride group of the PP-g-MA. The structure and proper-ties of PP/PP-g-MA/GO/G nanocomposites were compared by different techniques. Evidence of the nanoscale dispersion of graphite sheets within the PP were provided by wide-angle X-ray diffraction WAXD) and supported by scanning electron microscopy (SEM). The high mechanical shear stresses generated by the Gelimat greatly reduced the ordering initially measured by WAXD between graphite sheets and sheet aggregates, indicating a dispersion of the graphite in the polymer to the extent that graphite particles could hardly be observed by SEM. It was found that the addition of PP-g-MA and GO leads to excellent dispersion of G within the PP matrix. The flow behavior of the material was also studied by means of a parallel-plate rheometer. The addition of graphite to PP caused a drastic change in the flow behavior of PP. The thermal degradation behavior, studied using thermogravimetric analysis (TGA), showed higher thermal stability of the nanocomposite than that of pure polypropylene. The dispersion of the graphite in the resin promoted the nucleation of beta crystallites in PP. The beta crystallites, normally less abundant than alpha crystallites in pure PP, were found to constitute the dominant phase in the nanocomposite. (C) 2004 Society of Plastics Engineers.