# Formation of Conductive Networks in Polysulfone Filled with Graphite-Derived Materials
## 3 Results and Discussion
### Thermal Conductivity  
Because of the high thermal properties of NG due to its layered structure, increasing the content of NG in the composite can improve thermal conductivity. Furthermore, well-dispersed graphite particles ensures good thermal contact and effective heat conduction, implying that increased loadings of graphite particles might improve heat transmission inside the material. In addition to the excellent crystalline structure, high aspect ratio, and large crystallite size of NG, the composite filled with NG as a filler has the best thermal conductivity, where the NG particles lay on each other and form big contact areas, which leads to reaching a higher conductivity. And as the filler content is higher than 50 wt. %, the composite density became higher, and the NG particles compacted with each other with fewer pores, which led to a bigger increase in thermal conductivity. Thus, using AG as a filler, the thermal conductivity seems to increase rapidly as the filler content increases, causing the filler particles to be in close contact with one another. Figure 8: The dependence of thermal conductivity on density of PSU-based composites filled (**a**) with NG, AG, NG + CB, and AG + CB and (**b**) with CB when the heat direction is perpendicular to the filler particles. Figure 9 shows that the maximum thermal conductivity of the PSU-based composite was found to be of 17.47 W/m\(\cdot\)K and 3.45 W/m\(\cdot\)K for composites filled with 70 wt. % of NG and AG, respectively. In the case of using CB as a filler, which is made up of small particles of elemental carbon, there was no effect on the heat conductivity of the composite. We may explain this by the fact that carbon black particles establish contact points or junctions with one another, forming heat barriers. These contact sites obstruct direct heat transmission, lowering total thermal conductivity. As a result, despite the fact that carbon black possesses inherent heat conductivity, the contact resistance between particles restricts its real influence. Because of the shape compatibility of the filler particles, the introduction of 4 wt. % CB with synthetic graphite improved the thermal conductivity of the composite, resulting in the construction of continuous thermal channels between the filler particles. The opposite effect was observed when CB was combined with NG, where CB separated the natural graphite sheet, resulting in a reduction in thermal conductivity of the composite, as is shown in Figure 10.  
Because of the strong carbon-carbon bonding within the layers, graphite is a highly conductive substance along its basal plane. However, because of the weaker interlayer  
Figure 10: Thermal conductivity in the direction normal to sample plane as function of filler content of PSU-based composite filled with NG; AG, NG + CB and AG + CB at 25 \({}^{\circ}\)C.  
Figure 9: Thermal conductivity in the direction normal to the sample plane as a function of the filler content of PSU-based composite filled with NG; AG and CB at 25 \({}^{\circ}\)C.  
bonding, thermal conductivity perpendicular to the planes (through-plane conductivity) is often lower. When graphite is incorporated into a polymer matrix, the orientation and interfacial contact between the graphite particles and the surrounding polymer matrix can impact the composite's thermal conductivity as is shown in Figure 1.  
Increasing the amount of graphite in the composite can improve heat conductivity. Increasing the volume percentage of graphite in the composite can take advantage of its high heat conductivity. However, graphite loading generally has an upper limit before declining results are detected. The particular thermal conductivity values of the polymer composite filled with natural graphite will be determined by the exact composition, manufacturing factors, and graphite material utilized, and they may be enhanced based on the fillers employed. CB was employed as a second filler with NG in this example.