Multifunctional material design for strain sensing: carbon black effect on mechanical and electrical properties of polyamides

This work investigates the coupled effect on mechanical and electrical properties of carbon black dispersed in polyamide 6 and 6.6 matrices. The CB content is varied between 15 % and 25 % wt. The elastic modulus in-creases of 12 % by increasing the CB concentration. Results reveal the capability of CB to functionalize ther-moplastic polymers by activating conductive networks, as obtained over the percolation threshold of 13 % wt. The conductivity sensitivity to the mechanical strain is analyzed within direct (DC) and alternate current (AC) in the range of 0-100 kHz. Composite with lower CB concentrations exhibited a linear increase of the Gauge Factor (GF) with the frequency (from 2 to 4 at 20 %wt), while at 25 % wt of CB, the GF is 17 in DC regime and linearly decreases toward 6, at 100 kHz. A novel model for the estimation of the material Gauge Factor (GF) variation with the applied electric frequency is proposed.