Effects of Graphene on Twisting of High Density Polyethylene

Abstract

High density polyethylene (HDPE) is known to form banded spherulites when crystallized from the melt. In such spherulites, concentric bands of alternating light and dark colors emanating from the spherulite nucleation center are observable between cross polarizers and appear as a function of the anisotropy of the dielectric susceptibility as crystal orientations continuously rotate about the growth direction. Recently, we identified PE to be a promising compound to induce twisting in conjugated carbonaceous systems, such as triisopropylsilylethynyl anthradithiophene (TIPS ADT). When blended together in ratios between 10 – 70 wt.% PE, TIPS ADT and PE crystals twist in concert with one another to form composite films of intertwined helicoidal fibrils. In this work, we investigate crystal twisting in HDPE-graphene oxide composites. In addition to its unique multifunctionality, graphene has also recently demonstrated peculiar twisting capabilities that strongly alter its physical properties. Here, we first produce graphene sheets through the chemical oxidation of natural graphite, and then investigate the influence of graphene on the twisting of HDPE composites under various processing parameters (graphene concentration, polymer cooling rate, etc). HDPE-graphene composites have been prepared using melt extrusion in the form of microfibers and films. We measured the influence of twisting on the mechanical and electrical properties of the composites, as well as the crystallographic structure using optical and electron microscopy, and X-Ray diffraction spectroscopy.