Polypropylene composites with finely dispersed multi-walled carbon nanotubes covered with an aluminum oxide shell

A one-pot three-step, scalable procedure leads to composites of isotactic polypropylene with consistently finely dispersed multi-walled carbon nanotubes (CNT). The essence of the procedure is to generate a fine dispersion of single carbon tubes in toluene using sonication and impregnation of the CNTs with methylaluminoxane (MAO). MAO reacts with CNTs to yield methane in a period of hours. Composites with 0.1–1.2 wt% CNTs were formed by inflicting a subsequent in-situ polymerization in the CNT/MAO dispersions and are showing clustered single tube distributions. The electrical percolation was found below the theoretical value at 0.5 wt% CNTs. Alumina forms at the surface of the CNT filler and builds the interface to the matrix polymer. The crystallization of the composites leads to α-spherulites typical for alumina nucleation; the Avrami coefficient was close to 3. The tensile strength increases by a maximum of 7% at a CNT loading of 0.2 wt%. The elongation at break is below 100% for composites with a CNT content over 0.4 wt%, indicating a limited adhesion at the PP-alumina-CNT interfaces.