## 3 Results and Discussion
### Filler Content, Flowability, and Sintering Window  
The filler percentage was chosen according to preliminary fabrication test trials that enabled the definition of the threshold beyond which the occurrence of defects would compromise the integrity of the component. For weight percentages higher than 10%, during the sintering process, printing defects began to occur, i.e., the initiation of cracks along the perimeter areas of the printed components and warping of the edges, as highlighted in Figure 4. This figure compares samples produced with different nano-graphite contents during the fabrication process, i.e., successfully produced specimens with 10% xGNPs, including dog-bone-shaped samples for tensile testing and square samples for electrical conductivity measurements, alongside samples with 12% xGNPs, which exhibited deformation that compromised the laser sintering process. It is worth noting that square samples are not shown for the formulations at higher concentrations, as the number of layers that could be fabricated was insufficient to allow photographic documentation. These defects could have stemmed from enhanced light absorption and the thermal conductivity of nano-graphite compared to the surrounding nylon-12 powder [50], creating perimeter zones with an excessively high thermal gradient, which, due to residual stresses, led to cracks and discontinuities in the powder.  
The compressibility index and the Hausner ratio are crucial in understanding the flow properties of powders. Low values, i.e., \(CPR\) < 20% and \(HR\) < 1.25 [51], promote uniform mixing, i.e., ensuring consistent distribution of constituents; efficient processing, i.e., powders move smoothly under the action of the recoater during the deposition, thus minimizing blockages; and densification, i.e., powders compress easily. As can be seen in Figure 5, all the mixtures present \(CPR\)s < 15% and \(HR\)s < 1.18, thus assuring a good flowability. It is worth noting that the addition of the xGNPs promoted reductions in both indices, which were lower the higher the percentage added, i.e., from \(CPR\)\(\cong\) 13.8% and \(HR\)\(\cong\) 1.16 for the starting powder to \(CPR\)\(\cong\) 10.7% and \(HR\)\(\cong\) 1.12 for the highest percentage of xGNPs. This finding can be attributed to the small thickness of the nanoplatelets, which would occupy the gaps created by the larger PA12 particles [52].  
The addition of xGNPs can also affect the sintering window, shifting the characteristics peaks of the DSC curve and therefore the onset temperatures of melting and recrystallization, as shown in Figure 6 and Table 4. The observed trend suggests a widening of the sintering window from 15.9 \({}^{\circ}\)C for the PA12 matrix up to 16.2 \({}^{\circ}\)C for 10% of xGNPs. In particular, the shift of the recrystallization temperature to higher values can be attributed to the nucleating effect of the xGNPs that prevents the mobility of polymer chains [22]. The same can be said for the melting point, since it requires a greater amount of heat of fusion to increase the temperature of the sample, resulting in a more pronounced melting peak [53]. However, the change in the sintering window extent is very small and the same process parameters of the pure PA12 can be adopted to fabricate the composite samples at varying xGNP concentrations (see Table 3).  
Figure 4: Frames of (**a**) successfully fabricated samples with 10% xGNPs (dog-bone-shaped samples for tensile testing and square samples for electrical conductivity measurements) and (**b**) compromised samples with 12% xGNPs due to crack formation along the perimeter interface (as indicated by the red arrows).  
Figure 5: Comparison of flow character exhibited by Hausner ratio/compressibility index values and experimentally obtained flow rate. The asterisks represent the \(HR\) values for varying xGNPs content.