In-situ polymerization of isotactic polypropylene-nanographite nanocomposites

Abstract

Isotactic Polypropylene-Exfoliated Graphene Nanoplatelet (iPP-xGnP TM ) nanocomposites were prepared through an in-situ polymerization technique and compared to analogous composites prepared by melt compounding. In-situ preparation of iPP-xGnP nanocomposites was accomplished via single site metallocene polymerization of propylene within a toluene dispersion of xGnP nanoparticles. The in-situ prepared nanocomposites were compared to analogous nanocomposites prepared by melt compounding of commercial Ziegler-Natta iPP with xGnP. Optical microscopy showed the in-situ prepared nanocomposites demonstrated poorer xGnP dispersion compared to composites prepared by melt compounding. All xGnP-reinforced nanocomposites demonstrated increased crystallization temperature, as well as increases in mechanical strength and modulus, relative to neat iPP. However, the non-linear mechanical properties were found to be influenced by the both the preparation method and nanoparticle loading. Nanocomposites prepared by in-situ polymerization generally demonstrated superior ductility and fracture toughness compared to composites prepared by melt compounding. The results are discussed with regard to the preparation technique and xGnP loading. IntroductionPolyolefin nanocomposites offer opportunities to improve the properties of polyolefins with relatively small amounts of reinforcement. Compared to traditional fiber-reinforced composites, nanocomposites only require small reinforcement concentrations (< 2 vol %) to create property improvements. Polyolefin nanocomposites have shown property improvements such as M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 mechanical reinforcement, controlled gas permeability, and increased electrical conductivity when compared to the neat polyolefin resins [1].Many researchers strive to improve the mechanical properties of polyolefins using nanoscale reinforcement in order to create new and economical materials. For example, interest in the automotive industry has been directed toward developing reinforced polyolefins to replace engineering thermoplastic and metallic automotive materials, enabling cost and weight savings [2]. Polyolefin nanocomposites are ideal materials for this application due to the availability of low cost nanoscale reinforcements and polyolefin resins.Recently, graphene nanoplatelets (GNPs) have been investigated as nanoreinforcements for polyolefins [3,4]. The production of GNPs can be achieved by the thermal exfoliation of mineral graphite. Most notably, Drzal et al. developed an efficient method to produce Exfoliated Graphene Nanoplatelets (xGnP TM ) using acid intercalation followed by microwave assisted exfoliation [5,6]. These nanoplatelets are ideal nanoscale reinforcements due to their high aspect ratio, surface area, stiffness, thermal conductivity, and nucleation efficiency for crystallization of polyolefins [3,4,7,8]. Typically, polyolefin-GNP nanocomposites demonstrate improved modulus, strength, and higher crystallization temperature, along with decreased st...

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