THE USE OF SUPERCRITICAL CARBON DIOXIDE TO PRODUCE POLYCARBONATE/NANOTUBE COMPOSITES WITH IMPROVED ELECTRICAL CONDUCTIVITY

摘要

Supercritical carbon dioxide (scCO_2) treatment of carbon nanotubes (CNT) has led to improvedrnproperties of thermoplastic nanocomposites with minimal damage to the CNT aspect ratio. Inrnthis work, the supercritical carbon dioxide treatment of CNT was optimized to enhance thernbundle separation by using fundamental thermodynamic principles. Furthermore, the scCO_2rnmethod was applied to the previously developed scCO_2 aided melt blending method to formrnpolycarbonate/ nanotube composites with different degrees of nanotube separation. Bulk densityrnmeasurements and transmission electron microscopy (TEM) were conducted to investigate therneffect of different processing conditions on the separation of nanotube bundles and ensure thatrnthe nanotubes destruction was minimized. Conductivity was measured to examine the effect ofrnthe optimized scCO_2 processing on the final composite properties. It was found that an optimalrnexpansion was obtained at soak temperatures and pressures corresponding to a CO_2 fluid densityrnof ～730 kg/m~3. This resulted in an expansion factor of～12 fold by volume compared to pristinernnanotubes. The composite prepared with 3 wt % nanotubes at the optimal degree of nanotubernseparation showed a surface conductivity of 5.71 × 10~(-5) Siemens (S), compared to 9.16 × 10~(-6) Srnwithout scCO2 treatment. It was found that beyond a critical degree of nanotube separationrn(expansion factor of ～5 fold), conductivity failed to improve appreciably. Improved mixingrntechniques may result in continuing improvement in conductivity when combined with thernscCO_2 treatment.