Property improvement of multi-walled carbon nanotubes/polypropylene composites with high filler loading via interfacial modification

Although carbon nanotubes (CNTs) exhibit excellent performance, they are prone to agglomeration because of their high surface energy and large specific surface area. Moreover, CNTs are hardly compatible with polymers due to their nonpolar properties, as manifested by the less stable interface between these two components. This study was aimed at improving the compatibility between multi-walled carbon nanotubes (MWNTs) and polypropylene (PP). Herein, a practical strategy for the modification of MWNTs and the subsequent fabrication of polypropylene-grafted multi-walled carbon nanotubes (PP-g-MWNTs) are reported. The morphology of the as-obtained PP-g-MWNTs was observed using a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a polarizing microscope, whereas their elemental composition and bond structures were characterized by Fourier transform infrared (FT-IR) spectroscopy, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) was used for crystallographic analyses. A performance comparison between the PP-g-MWNT samples and the undecorated samples was conducted based on the results obtained via dynamic mechanical analysis (DMA), tensile testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Serial characterizations proved the successful grafting of PP molecular chains onto the MWNT surfaces. Thus, the MWNTs, the filler phase, could be included into the PP matrix covalently and thus existed as an integrated component of the composite system. As a consequence, the specific design of PP-g-MWNTs remarkably improved both thermal and mechanical properties of the PP composites.