# Mechanical and Conductive Behavior of Graphite Filled Polysulfone-Based Composites
## 3 Results and Discussion
### Thermal Conductivity
The maximum thermal conductivity of the PSU-based composite filled with 50 wt.% NG, 70 wt.% AG and 70 wt.% EG reached 7.35 W/m - K, 4.45 W/m - Kand 5.05 W/m - K, respectively, as shown in Figure 9. We can notice the difference between 50 wt.% NG, AG and EG as filler--the high thermal conductivity of the composite based on natural graphite as a filler has the best thermal conductivity due to the high aspect ratio and large size of NG's crystallites, in addition to its crystal structure being closer to an ideal single-crystal material than AG and EG. As the content of NG was raised above 50 wt.% the thermal conductivity started decreasing; this phenomenon could be explained by the aggregation of PSU/Gr in addition to the pore defects of the composite. As the filler content was raised, the density started decreasing and after using 50 wt.% of EG it started rising which was explained in Section 3.2. This can be attributed to the variation in thermal conductivity when EG is used as a filler. We can see that the pores affect the thermal conductivity, but as the composite became denser the thermal conductivity increased. In addition, the agglomerations became bigger for EG and AG and the pores became more numerous. We may assume from SEM images that the porosity of the composite, which increased as the filler amount increased, prevented the conduction routes from effectively transferring heat. [PERSON] et al. [38] investigated the effect of increasing the graphite filler content on the thermal conductivity in polyamide 6/graphite composite and found that the thermal conductivity improves with increasing the filler concentration. The maximum thermal conductivity was 28 W/m. K when 75 wt.% graphite was used. The thermal conductivity was 9 W/m - K by using 50 wt.% of graphite, which is less than the value we were able to  
Figure 9: Thermal conductivity as function of filler content of PSU-based composite filled with NG (1); AG (2) and EG (3) at 25 \({}^{\circ}\)C.  
attain using 50 wt.% of natural graphite as filler. We can conclude from their results that they achieved superior filler dispersion in the polymeric matrix compared to our findings, since polysulfone and polyamide have distinct characteristics. [PERSON] et al. [39] also employed PSU as a matrix to manufacture the composite, and applied injection molding while employing carbon fiber as a filler up to 26 vol.%. The best thermal conductivity they could achieve was 1 W/m \(\cdot\) K. According to their SEM analysis, the majority of the skin layer's fibers are randomly distributed along the X-Z axis and connect to one another to form a thermal conductivity pathway. In comparison to the core layers, the skin layer is crucial in enhancing the thermal conductivity of composite materials. The thermal conductivity of the samples with different filler content and their densities were measured, in order to investigate the relationship between thermal conductivity and material density. Measures were taken of the samples which were used in this work and in the previous work. Figure 10 shows that when material density grows, thermal conductivity also rises as a result of the opportunity for conducting bridges forming between the polymer and the graphite. The thermal conductivity increased dramatically as the density rose above 1.5 g/cm\({}^{3}\). Thermal conductivity increased with increasing density, particularly in the case of PSU/NG. This increase was due to the solid phase created by the mixture of PSU and thermally conductive Gr becoming more and more important for heat conduction.