The nucleating effect of exfoliated graphite nanoplatelets and their influence on the crystal structure and electrical conductivity of polypropylene nanocomposites

The focus of this research is to investigate how exfoliated graphite nanoplatelets, xGnP™, (graphene sheets ∼10 nm thickness, ∼1 μm diameter), a nanomaterial developed by the Drzal group, affects the crystallization of semicrystalline thermoplastics i.e., polypropylene (PP). In addition, this study explores how the presence of xGnP in combination with the processing conditions used to make the xGnP-PP nanocomposites alter the crystal structure and electrical conductivity of these systems. The nanocomposites are fabricated (i) by melt mixing followed by injection molding and (ii) by coating PP powder with xGnP with sonication in isopropyl alcohol followed by compression molding. PP was found to nucleate on the graphene surface of xGnP that is an effective nucleating agent for the β-form of PP crystals at low concentrations. The β-form of PP crystals has higher impact strength and toughness compared to the more common occurring α-form. It is found that the aspect ratio and concentration of xGnP combined with the crystallization conditions can be used to engineer the crystal structure such as the population and size distribution of PP spherulites and alter the electrical conductivity of xGnP-PP nanocomposites. The reason is that the presence of many small spherulites nucleated by the xGnP disrupts the percolated network formed by the conductive particles and thus increases the concentration required to reach conductivity and alters the conductivity value.