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 (~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 ~350 μm aligned bundle (l-MWCNT) and short length of 1.5 μm (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 × 10−3 S cm−1 for 0.5 wt% l-MWCNT and 0.95 × 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.