# Electrically Conductive Nanocomposite Fibers for Flexible and Structural Electronics
## 3 Results and Discussion
### Electrical Properties
Composites M3, M4, and M5, containing both of the above functional phases, showed a high resistivity constancy independent of the applied voltage. This was due to the superposition of the properties characteristic of graphite and CNTs. \begin{table}
\begin{tabular}{l c c c c c} \hline  & & **Average** & **Maximum** & **Minimum** & **Coefficient of** \\  & & **Resistivity [\(\Omega\)m]** & **Resistivity [\(\Omega\)m]** & **Resistivity [\(\Omega\)m]** & **Variation (V)** \\ \hline \multirow{4}{*}{\(\Omega\)**} & G6 & 0.0412 & 0.0422 & 0.0407 & 0.0101 \\  & C2 & 0.790 & 0.837 & 0.771 & 0.0186 \\  & C3 & 0.00213 & 0.00264 & 0.000975 & 0.265 \\  & M3 & 0.271 & 0.284 & 0.267 & 0.0157 \\  & M4 & 0.0738 & 0.0743 & 0.0735 & 0.00303 \\  & M5 & 0.0275 & 0.0280 & 0.0272 & 0.00509 \\ \hline \end{tabular}
\end{table} 
Table 3: Resistivity values of the selected composites fibers with a 0.5 mm diameter. As the developed composite fibers may be used in the textile industry, they should have mechanical properties that are no worse than the fabrics in which they will be placed. The fabric material must be resistant to the influence of external forces causing the change of its shape. The individual fibers in the fabric were mainly exposed to tensile and compressive forces. According to this, one of the most important mechanical requirements composite fibers must meet is sufficient maximum elongation. Typical textile fabrics, such as cotton, silk, and wool, and polymer fabrics, such as polyester, have an extension ratio from 7% to 40% [33; 34; 35]. According to these values, during the research, it was decided that the fibers must have a minimum of 40% elongation without breaking to be considered as meeting the basic mechanical requirements. In addition, it was desirable that the composite fibers in this range of stretches did not increase their resistance significantly. A change in resistivity in the range of several hundred percent may allow the developed materials to be used as  
Figure 2: Changes in resistivity under different voltages compared to resistivity at 12 V for different composites; (**a**) excluding the C3 composite and (**b**) including the C3 composite. strain sensors located directly in textile materials. However, more significant changes in resistivity could cause difficulties in using composite fibers to transmit and receive electrical signals, or to power electronic components in textronic systems. The present paper analyzed the effect of strain on the change in resistance of the composite fibers. The relative resistance change versus the extension ratio is shown in Figure 3. It was observed that the resistance of each fiber increased in a different way, depending on the filler type. The resistance of the G6 composite rapidly increased, even for a low extension ratio. On the other hand, the C3 composite containing CNT as the functional phase, had a much smaller increase in resistance during the entire tensile test until rupture. Composites containing a mixture of CNTs and graphite as the functional phase, presented a change in the resistance similar to the C3 composite, especially for the extension ratio below 40% (Figure 3b). Figure 3: Dependence of relative resistance on elongation, for 0.5 mm diameter composite fibers, (**a**) for the maximum extension ratio, and (**b**) for and extension ratio of up to 50%.