Effect of acid modification on electrical properties of carbon nanotube/epoxy resin composites

Carboxyl-functionalized multi-walled carbon nanotube(C-MWCNT) was prepared by mixed acid method using original carbon nanotube(R-MWCNT). Two types of multi-walled carbon nanotube/epoxy resin nanocomposites were prepared respectively. Infrared spectrum and scanning electron microscope revels that this method cuts off carbon nanotubes effectively and grafts small amount of hydroxyl and carboxyl groups on the surface. Test shows that the volume resistivity of C-MWCNT/EP is 8 to 11 magnitudes higher than that of R-MWCNT/EP. Percolation threshold of R-MWCNT/EP is about 0.03wt.% while C-MWCNT/EP does not show percolation within test filler content. J-E curves of R-MWCNT/EP shows strong nonlinear behavior which matches the characteristic of field emission while no obvious relation is found in the case of C-MWCNT/EP. Dielectric spectrum shows the addition of C-MWCNT does not change the polarization mechanism of epoxy resin while R-MWCNT/EP shows a complete different dielectric spectrum pattern. The changes on dielectric behavior and electrical conductivity are due to the change of CNT structure and CNT-EP interface, which is mainly caused by acid modification.