Liquid Phase Exfoliation of Graphite to Graphene & its Applications in Polymeric Nanocomposites

Abstract

Nanocomposites are superior to conventional one in terms of its mechanical performance. Pristine /functionalized graphene sheets (FGS) were incorporated into a range of model polymers. Solvent aided blending was adopted for better dispersion of FGS and graphene sheets in these polymers. Graphene was added to selected polymers like polyurethane (PU), poly (vinyl chloride) (PVC), poly (acrylonitrile) (PAN), poly (vinyl alcohol) (PVA) and poly (vinyl acetate) (PVAc) in order to improve the mechanical performance of these materials. Different forms of graphene nanosheets like pristine/FGS with different lateral dimensions were selected in order to study its effects on the mechanical performance of selected polymers in terms of young’s modulus, tensile strength and elongation at break. Graphene nanosheets were functionalized with octadecylamine and were incorporated in polyurethane and it was observed that 2.5 vol% is the mechanical percolation level for this polymer as above this loading there was improvement in the mechanical performance of polyurethane while at this loading the elongation at break was suffered slightly. Similarly in case of poly(vinyl chloride) a critical loading(1.5wt%) was observed at which there was improvement in mechanical properties of these polymers and almost no elongation at break was observed for this loading and the modulus determined in this case was superior to calculated from Halpin-Tsai equation. Two type of graphene nanosheets with different flake size (one and 3.5 micron) were incorporated in poly (acrylonitrile). Its comparative study was conducted it was observed the big flake improved the performance of polymers in terms of modulus and UTs while the response of small flake in terms of elongation at break was better than big flakes. Large area graphene oxide were synthesized and were introduced to poly(vinyl alcohol) and the role of these nano fillers were very pronounced in terms of modulus, UTS and elongation at break was not disturbed but slightly improved. Graphene flakes were studied through transmission electron microscopy(TEM) and Raman spectroscopy while dispersion of these flakes were in selected polymers was confirmed by scanning electron microscopy(SEM) and the mechanical performance of these nanocomposites were conducted on Zwick-Roell tensile tester. Graphene-based polymer nanocomposites can be a new versatile soft material with numerous advantages. Graphite was exfoliated to graphene using NMP and water as solvent as well. 63mg/ml concentration was obtained during tip sonication in NMP while in case of water as media the maximum concentration obtained was 7mg/ml using sodium cholate as surfactant. The concentration of graphene nanosheets were studied through UV-visible spectroscopy while quality of flakes was studied through TEM and Raman spectroscopy.