Ultra-high molecular weight polyethylene nanocomposites reinforced with novel surface chemically modified sonic-exfoliated graphene

Abstract

A sequence of chemical modifications was performed on natural graphite flakes from initial oxidation, producing graphene oxide (GO), followed by thermally-reduced graphene expansion (GE) to a final sonic exfoliation forming nanoparticles (GES). Employing Raman spectroscopy, it is found that the graphite ID/IG intensity ratio of 0.86 was substantially decreased to 0.54 for GES, indicating a smaller number of more ordered graphene sheet layers. The crystalline index (CI) obtained by X-ray diffraction of the final sonic-exfoliated GES (48%) is improved in comparison to the expanded GE (31%), suggesting better-organized sheets. Scanning electron microscopy shows GES with decreasing stacking of almost transparent layers due to increased spacing between graphene sheets. Nanocomposites fabricated with 0.05, 0.1, 1.0, 3.0, and 5.0 wt.% GES incorporated into ultra-high molecular weight polyethylene, lubricated with mineral oil (UHMWPE/OM), disclosed superior CI and higher temperatures for the onset and maximum rate of thermal degradation. Dynamic mechanical analysis reveals improved viscoelastic stiffness from 1 up to 3 wt.% of GES incorporation, indicating that this novel graphene-based GES acts as reinforcement for UHMWPE/OM nanocomposites. In particular, the 3 wt.% GES nanocomposites with the best thermal and mechanical performance as well as enhanced processability might be considered a practical option for replacing structural applied common UHMWPE.