Effect of length of carbon nanotubes on electromagnetic interference shielding and mechanical properties of their reinforced epoxy composites

The high performance-multiwalled carbon nanotubes (MWCNTs) reinforced epoxy resin nanocomposites have been fabricated using industrially viable fast process of dispersion with high speed homogenizer (similar to 30,000 rpm). This high energy homogenizer was found to be a successful technique for uniformly dispersion of MWCNTs and confirmed by scanning electron microscopy. Herein, two different lengths of MWCNTs, i.e., long length of similar to 350 mu m aligned bundle (l-MWCNT) and short length of 1.5 mu m (s-MWCNT) were used as reinforcement in epoxy resin. The effect of length of MWCNTs on the mechanical, electrical, and electromagnetic interference (EMI) shielding properties of MWCNTs/epoxy nanocomposites is investigated. The percolation threshold was obtained at 0.02 wt% for l-MWCNT compared to 0.11 for s-MWCNT. Due to very low percolation threshold and enhanced electrical conductivity (1.37 x 10(-3) S cm(-1) for 0.5 wt% l-MWCNT and 0.95 x 10(-3) S cm(-1) for 0.5 wt% s-MWCNT), absorption dominated EMI shielding effectiveness was achieved -16 dB for l-MWCNT compared to -11.5 dB for s-MWCNT with 0.5 wt% loading in Ku-band (12.4-18 GHz). This is the highest reported value for MWCNTs-epoxy composites for low loading level of 0.5 wt% at 2.5-mm thickness. In addition to this, flexural strength of the composites was found to be 125 MPa at 0.3 wt% for l-MWCNT and 113 MPa at 0.3 wt% for s-MWCNT from 95 MPa of pure cured epoxy suggesting the usefulness of this of material as strong microwave absorber.