Using supercritical CO2-assisted mixing to prepare graphene/carbon nanotube/epoxy nanocomposites

In this study supercritical carbon dioxide (scCO(2)) was employed to incorporate graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) into an epoxy matrix to enhance the electrical and thermal properties of the epoxy. The percolation threshold for electrical conductivity for the nanocomposite prepared through scCO(2) mixing was 2 wt%, one-third that obtained after acetone mixing. When the weight ratio of GNPs to MWCNTs was 1:3, the electrical conductivity (2.6 x 10(-7) S/cm) of the GNP/MWCNT/epoxy nanocomposite prepared through scCO(2) mixing at 35 degrees C and 1200 psi was twice that obtained when using subcritical CO2 mixing at 30 degrees C and 1000 psi. On the other hand, when the weight ratio of GNPs to MWCNTs was 3:1, the thermal conductivity (0.89 W/mK) of the nanocomposite prepared using scCO(2) was 287% higher than that of the neat epoxy. A synergistic effect of the GNPs and MWCNTs was observed, with 68 and 190% increases in the thermal conductivity of the GNP/MWCNT/epoxy nanocomposite over the individual GNP/epoxy and MWCNT/epoxy nanocomposites, respectively, after applying scCO(2) mixing. The proposed scCO(2) mixing process not only aids the dispersion of GNPs and MWCNTs in epoxy but also eliminates the presence of solvent after decreasing the pressure. (C) 2015 Elsevier Ltd. All rights reserved.