Comparative analysis of electric, magnetic, and mechanical properties of epoxy matrix composites with different contents of multiple walled carbon nanotubes

Epoxy composites based on aligned chemical vapor deposition-grown multiwall carbon nanotubes (MWCNTs), containing trapped iron nanoparticles, with weight fractions ranging from 0.03 to 1 wt%, were produced following a well-known processing way. Electrical and mechanical properties as well as their densities were measured. The results are compared with previous studies investigating the magnetic percolation behavior in the same samples of composites. A percolation threshold at 0.4 wt% of MWCNTs was determined by the electrical property and it agrees with the threshold observed in the magnetic properties. A hop in the porosity and a depression of the bulk mechanical properties were also found at the threshold value. These results point out that there is an efficiency threshold related to the sonication stage of the fabrication process and the weight fraction of MWCNTs, and after this threshold, the initial nanotubes pans were not separated into individual MWCNTs or into small ropes. An optimized sonication stage is proposed and the improvement in the dispersion of the filler is shown.