Electrically Insulated Epoxy Nanocomposites Reinforced with Synergistic Core–Shell SiO2@MWCNTs and Montmorillonite Bifillers

With unique physicochemical properties, multiwalled carbon nanotubes (MWCNTs) have enabled major achievement in polymer composites as reinforcing fillers. Nevertheless, high conductivity of raw MWCNTs (R-MWCNTs) limits their wider applications in certain fields, which require outstanding thermal conductivity, mechanical, and insulation properties simultaneously. In this article, silica (SiO 2 ) coated MWCNTs core–shell hybrids (SiO 2 @MWCNTs) and organically modified montmorillonite (O-MMT) are employed to modify epoxy (EP) simultaneously. The epoxy-clay system is cured by using anhydride curing agent. The impact strength and flexural strength of final nanocomposites are greatly improved. Meanwhile, the final composites remain in high electrical insulation. Compared to mixed acid treated MWCNTs (C-MWCNTs) (0.5 wt%)/EP nanocomposites, the volume resistivity of the O-MMT(4 wt%)/SiO 2 @MWCNTs(0.5 wt%)/EP nanocomposites increases more than six orders of magnitude. Synergistic toughening effect occurs when using core–shell SiO 2 @MWCNTs and MMT bifillers. The electrical insulation is attributed to the suppressed electron transport effect by SiO 2 layer on the CNTs surface, and the blocked conductive CNTs network by the buried 2D structural O-MMT. The SiO 2 @MWCNTs core–shell hybrids also benefit to decrease the dielectric constant and dielectric loss of CNTs/EP composites. This work provides guidance to using CNTs as reinforcement fillers to toughen the polymers for electric insulating applications.