Fabrication of polypropylene/carbon nanotubes composites via a sequential process of (rotating solid-state mixing)-plus-(melt extrusion)

In this study, a simple but effective method to realize excellent comprehensive performances in polypropylene (PP)/multi-walled carbon nanotubes (MWNTs) was developed. Before melt extrusion, solid-state iPP powders and MWNTs were pre-mixed upon high-speed rotating. By this way, the dispersion extent of nanotubes was significantly improved as comparing to the common one-step melt extrusion strategy. As validated by scanning electron microscopy, most of MWNTs exist as a form of filament bundles with size of hundreds nanometers; no obvious agglomerate was found even at high MWNTs content, 5%. The improvements of the major mechanical properties and electric conductivity were much efficient for the composites obtained via the two-step process of rotating solid-state mixing (RSSM)-plus-melt extrusion. The tensile strength, Young’s modulus and impact strength at 5% MWNTs content were enhanced for 35%, 42% and 45%, respectively, indicating an excellent strength–rigidity–toughness balance, which was hardly achieved in polyolefin/carbon nanotubes composite. It is believed that the method developed in this study is so far the most effective and convenient for efficiently dispersing nanotubes into the nonpolar, intractable thermoplastics and resulting in good properties, among a variety of fabrication method suggested in the previous researches. Importantly, the used RSSM equipment is a kind of frequently used dispersion machine, thus it has tremendous potential to be applied in industrial producing immediately.