## 3 Results
### SLS 3D Printing of PA12-Based Materials Containing Recycled TR  
A series of PA12-based materials loaded with different amounts of TR (10, 20, and 30 wt% with respect to the polymer matrix) were produced by SLS 3D printing. Increasing the TR content up to 40 wt% led to a clear decrease in the printed parts' shape resolution and printing quality. The resulted materials were identified as PA12, PA12/TR10, PA12/TR20, and PA12/TR30, where the TR content was 0, 10, 20, and 30 wt%, respectively. The morphological studies of the TR particles revealed irregular surface with complex elemental composition, as revealed by EDX analysis: 39.8% for C, 44.2% for O, 0.2% for F, 6.8% for Mg, 0.1% for Al, 8.6% for Si, 0.2% for S and 0.2% for Zn (Figure 3). TGA analysis was used to evaluate the thermal stability of pristine PA12, TR powder, and the corresponding composites. As presented in Figure 4, TR powder presented lower thermal stability compared to pristine PA12, and TR incorporation into PA12 induced a decrease in the onset values of the polymer composites degradation temperature (Td). In fact, at 5% weight loss during the TGA analysis, a decrease in the Td values was noticed from 419 \({}^{\circ}\)C for the pristine PA12 to 400, 372, and 365 \({}^{\circ}\)C in the presence of 10, 20, and 30 wt% TR powder, respectively (Table 1). This result is important and demonstrates that the incorporation of high TR loading could strongly impact the composite thermal  
Figure 3: SEM micrograph of TR microparticles surface and related EDX analysis. Figure 2: SEM micrograph of micronized TR powder (**A**) and TR particle size distribution (**B**). stability. Moreover, the incorporation of TR powder also affected the Td that decreases slightly between 465 and 470 \({}^{\circ}\)C, depending on the incorporated amount of rubber powder (Table 1). The obtained results guided us to limit the maximum loaded TR powder amount to 30 wt%. On the other side, it was found that the thermal stability of the PA12 was not significantly impacted after the printing process: Td before and after the printing step (IR laser diode irradiation, 5W and \(\lambda\) = 808 nm) was 451 and 458 \({}^{\circ}\)C, respectively. At the end of the TGA analysis of TR powder, a mineral residue of 41.2% at 800 \({}^{\circ}\)C was obtained, while for PA12, this residue was close to 2.5%. These data allowed us to determine the amount of TR in each of the printed composites by considering the final residue. For example, in the case of the printed PA12/TR10, PA12/TR20, and PA12/TR30 samples, it was found that the incorporated TR content was 9 \(\pm\) 0.4 wt%, 24.3 \(\pm\) 0.9 wt%, and 29.8 \(\pm\) 1.3 wt%, respectively (Table 1). This confirmed the suitable distribution of the TR powder within the polymeric matrix and validated the printing procedure as suitable for the fabrication of printed materials with desired rubber composition. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Td (\({}^{\circ}\)C)** & \
\begin{tabular}{c} **Td after 5 wt\% Weight** \\ **Loss (\({}^{\circ}\)C)** \\ \end{tabular} &
\begin{tabular}{c} **Resolute at 800 \({}^{\circ}\)C (\%)** \\ **Printed Samples (\%)** \\ \end{tabular} \\ \hline TR & 385 and 426 & 308 & 41.2 \(\pm\) 1.3 & n.a. \\ PA12 powder & 451 & 412 & 2.2 \(\pm\) 0.1 & n.a. \\ PA12 printed & 458 & 419 & 2.5 \(\pm\) 0.1 & n.a. \\ PA12/TR10 & 466 & 400 & 6.1 \(\pm\) 0.3 & 9.0 \(\pm\) 0.4 \\ PA12/TR20 & 468 & 372 & 12.2 \(\pm\) 0.5 & 24.3 \(\pm\) 0.9 \\ PA12/TR30 & 468 & 365 & 14.4 \(\pm\) 0.7 & 29.8 \(\pm\) 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: TGA analysis of TR, PA12/TR-based materials, and TR content in the printed materials. Figure 4: TGA thermograms of TR powder (**A**), PA12 printed sample and TR powder (**B**), and PA12(/TR) printed samples (**C**). In addition to the TR particle dimensions, several studies demonstrated that the relative content in rubber particles greatly affects the composite final properties.