# Formation of Conductive Networks in Polysulfone Filled with Graphite-Derived Materials
## 3 Results and Discussion
### Mechanical Properties  
ISO 291: 2008 and ASTM D790 [41] standards were used to conduct three-point flexural testing. The test was carried out using universal testing equipment manufactured by Zwick Roell (Group, Ulm, Germany). Using a hot press, the samples were formed into rectangles (\(80\times 10^{3}\) mm). The flexural strength magnitude for unfilled PSU was found to be about 124 MPa, and the maximum achieved value for composite containing 30 wt. % of AG is 38.74 MPa, as shown in Figure 13. It shows that at a enough low filler content, the particles dispersed throughout the polymeric matrix well, which allows mechanical stresses to be transferred between two composites components. Increasing the filling degree induces a rise in the elastic modulus, which results in a corresponding decrease in deformability for all materials. Variations in the strength of a substance's qualities occur depending on the morphology of the filler. Figure 13 shows that when NG is used as a filler, the flexural strength depends strongly on the filler quantity, and the flexural strength maximum was achieved at 30 wt. % of the filler. Increasing the filler content is accompanied by decreasing the magnitude of flexural strength. Such a decrease may be associated with the fact that graphite sheets are piled on top of each other and overlapped to form a composite. The amount of interlayered polymer between the graphite particles reduces as the filler concentration increases, which results in lower adhesion capabilities and a reduction in the composite mechanical properties. Furthermore, in addition to the graphite sheets' structural pores, pores between the composite and the matrix appear at a high filling degree. As a consequence, we may conclude that increasing the filler amount decreases flexural strength because the graphite filler causes the polysulfone composite to become more brittle. Figure 14 shows the flexural test curves of PSU-based composites filled with CB, to study the effect of CB on the composite properties. Increasing the carbon black loading in the composite will typically reduce flexural strength. Carbon black particles have been shown in studies to disrupt the polymer matrix and function as stress concentrators, resulting in poorer interfacial bonding and lower mechanical characteristics. The lower filler concentration of CB indicates that the filler is effectively spread throughout the polymeric matrix, allowing mechanical loads to be transferred between the two components even with low filler amounts. Increased filling causes an increase in the elastic modulus, resulting in a decrease in deformability for all materials. Figure 13: Flexural test curves of PSU-based composites with unfilled PSU solution (1); 30 (2), 70 (3), wt. % of NG; 30 (4), 70 (5) wt. % of AG. To study the effect of adding CB as a second filler with graphite in composite material based on PSU, three-point flexural testing was applied as we can see in Figure 15. Incorporating CB with graphite in a composite may reduce the material's flexural strength. CB is a typical component used to increase the electrical conductivity of composites, but graphite is frequently added due to its outstanding mechanical qualities, such as high strength and rigidity. When CB is introduced to the composite, it spreads evenly throughout the matrix, producing conductive channels. The addition of CB, on the other hand, might disturb the structure and bonding between graphite particles, resulting in decreased interfacial strength. This can have a detrimental influence on the composite's flexural strength. Furthermore, the presence of CB has the potential to induce agglomeration, resulting in high concentration locations. These agglomerated patches can operate as stress concentrators, weakening the overall composite and leading to flexural strength loss. As one can see from Figure 15, the flexural strength of the composite filled with CB + NG did not change that much compared to the flexural strength of the composite filled with just NG.