## 3 Results and Discussion
### Effect of Filler Concentration and Combinations of Nanofililers on the Electrical Conductivity  
Traditional thermoplastic polymers are usually electrical insulators. Polymers containing electrically conductive fillers show interesting electrical properties like semiconductors and metals but without losing the processability of polymers. Typical applications are as anistatic (electrostatic dissipation) materials, electromagnetic interference shielding materials, heaters and sensors. Figure 5 and Table 3 represents electrical conductivity vs. GNP and MWCNT filler content for mono-filler (PLA/GNP and PLA/MWCNT and bi-filler (PLA/GNP/MWCNT) composites. Figure 4: Raman mapping of (**a**) D band, (**b**) G band and (**c**) 2D band of the same area for PLA/1.5 wt.% GNP/1.5 wt.% MWCNT composites. Figure 5: Electrical conductivity vs. GNP and MWCNT filler content for mono-filler (PLA/GNP and PLA/MWCNT) and bi-filler (PLA/GNP/MWCNT) composites. \begin{table}
\begin{tabular}{c c c c} \hline
**Composition Code (wt.\%)** & **Electrical Conductivity (S/m)** & **Thermal Conductivity** & **Thermal Diffusivity** \\  & & **(W/mK)** & **(mm\({}^{2}\)/s)** \\ \hline PLA & \(7.3\times 10^{-10}\) (\(\pm 3.39\times 10^{-10}\)) & 0.205 (\(\pm 0.0045\)) & 0.154 (\(\pm 0.0002\)) \\ PLA/1.5\% GNP & \(2.51\times 10^{-8}\) (\(\pm 1.48\times 10^{-9}\)) & 0.2695 (\(\pm 0.014\)) & 0.245 (\(\pm 0.0001\)) \\ PLA/3\% GNP & \(9.9\times 10^{-8}\) (\(2.97\times 10^{-8}\)) & 0.3748 (\(\pm 0.0011\)) & 0.3079 (\(\pm 0.0002\)) \\ PLA/6\% GNP & \(0.00835\) (\(\pm 0.00233\)) & 0.577 (\(\pm 0.0151\)) & 0.485 (\(\pm 0.0018\)) \\ PLA/1.5\% MWCNT & \(1.4\times 10^{-8}\) (\(\pm 2.83\times 10^{-9}\)) & 0.2275 (\(\pm 0.0026\)) & 0.1887 (\(\pm 0.0001\)) \\ PLA/3\% MWCNT & \(7.86\times 10^{-4}\) (\(\pm 4.86\times 10^{-4}\)) & 0.2612 (\(\pm 0.0026\)) & 0.1859 (\(\pm 0.0001\)) \\ PLA/6\% MWCNT & 0.021 (0.00707) & 0.303 (\(\pm 9.910\)-4) & 0.221 (\(\pm 8.7\times 10^{-4}\)) \\ PLA/1.5\% GNP/1.5\% MWCNT & \(5.4\times 10^{7}\) (\(+7.27\times 10^{-8}\)) & 0.3013 (\(\pm 0.0071\)) & 0.2339 (\(\pm 0.0002\)) \\ PLA/1.5\% GNP/4.5\% MWCNT & 0.0585 (\(\pm 0.0318\)) & 0.3779 (\(\pm 0.0031\)) & 0.2551 (\(\pm 0.001\)) \\ PLA/3\% GNP/3\% MWCNT & 0.036 (\(\pm 0.0112\)) & 0.4253 (\(\pm 0.0213\)) & 0.3138 (\(\pm 0.002\)) \\ PLA/4.5\% GNP/1.5\% MWCNT & 0.00244 (\(\pm 8.56\times 10^{-4}\)) & 0.4692 (\(\pm 0.0228\)) & 0.3971 (\(\pm 0.005\)) \\ \hline \end{tabular}
\end{table} 
Table 3: Electrical and thermal properties of mono-filler and bi-filler composites. Generally, the results show that at maximum filler content (6 wt.%) electrical conductivity increases almost 7-8 decades for the two-component systems with GNP and MWCNT compared with pure PLA, reaching the values of 8.4 \(\times\) 10\({}^{-3}\) (S/m) and 2.1 \(\times\) 10\({}^{-2}\) (S/m), respectively. Mono-filler systems on the base of MWCNT and PLA show higher values for electrical conductivity, especially at 3 wt.%, where a percolation threshold is reached. On the other hand, the bi-filler composites with PLA/1.5 wt.% GNP/4.5 wt.% MWCNT and PLA/3 wt.% GNP/3 wt.% MWCNT shows a synergetic effect of both nanocarbon fillers on electrical conductivity with the values higher than those observed for the maximum filler content of 6 wt.% of the mono-filler systems. The synergistic effects were attributed to the more efficient MWCNT network, resulting from the presence of GNPs, leading to a more homogeneous filler dispersion. Numerical studies focused on the electrical and thermal transport properties of hybrid nanocomposites indicated that synergy may arise from the presence of the flexible MWCNT rods, which favor the bridging of planar GNP nanoplatelets and thus facilitating the formation of a 3D network [39]. It seems that a combination of conductive carbon fillers (MWCNTs and GNP) enhanced electron transport across the junctions of GNP sheets and tubes, and thus a significant increase in the electrical conductivity of the composites was achieved and proved by the structural analysis.