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

- Supercritical CO2 is superior to acetone for dispersing GNPs and MWCNTs in an epoxy resin.
- Synergistic effect of GNPs and MWCNTs is observed for electrical and thermal conductivities.
- A factorial design was used to analyze the electrical conductivity responses.
- No solvent was retained in the prepared nanocomposites using scCO2 mixing.

In this study supercritical carbon dioxide (scCO2) 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 scCO2 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 × 10−7 S/cm) of the GNP/MWCNT/epoxy nanocomposite prepared through scCO2 mixing at 35 °C and 1200 psi was twice that obtained when using subcritical CO2 mixing at 30 °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 scCO2 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 scCO2 mixing. The proposed scCO2 mixing process not only aids the dispersion of GNPs and MWCNTs in epoxy but also eliminates the presence of solvent after decreasing the pressure.

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