## 3 Sample Preparation and Mechanical Tests  
PLA has a low glass transition temperature and tends to heat up and melt quickly with conventional machining processes. In accordance with the ISO 527 standard and the dimensions of the specimens, the cutting was carried out on a MAXIEM 1515 numerical control machine using the water jet cutting process enriched with abrasive sand. This allowed for a clean cut with precise dimensions. To avoid excess water effects, the samples are placed in a controlled atmosphere just after the cutting, before the mechanical tests are carried out. The nettle fibers and PLA were prepared at 60 \({}^{\circ}\)C and 2% humidity for 48 h before manufacturing and equilibrated under 50% humidity for 48 h at 25 \({}^{\circ}\)C before the mechanical tests. The measurements were carried out on five samples for each plate (Figure 10).  
Table 4 presents the mean values of Young's modulus, tensile strength, and elongation at break obtained for a sample of five specimens.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Samples from Plate (with Sorted Fibers and Raw Fibers)**} & \multicolumn{2}{c}{**Young’s Modulus (GPa)**} & \multicolumn{2}{c}{**Tensile Strength (MPa)**} & \multicolumn{2}{c}{**Elongation at Break (\%)**} \\ \cline{2-7}  & **Average** & **SD** & **Average** & **SD** & **Average** & **SD** \\ \hline SFUD\({}^{\circ}\) & 5.41 & \(\pm\)0.23 & 53.98 & \(\pm\)3.11 & 1.24 & \(\pm\)0.05 \\ RFUD\({}^{\circ}\) & 4.51 & \(\pm\)0.19 & 44.70 & \(\pm\)3.36 & 1.21 & \(\pm\)0.07 \\ SFUD45\({}^{\circ}\) & 3.85 & \(\pm\)0.08 & 35.89 & \(\pm\)2.58 & 1.19 & \(\pm\)0.10 \\ RFUD45\({}^{\circ}\) & 3.99 & \(\pm\)0.07 & 38.21 & \(\pm\)3.64 & 1.24 & \(\pm\)0.12 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Summary of tensile tests (1 mm/min) on unidirectional SF and RF.  
Figure 9: Nettle fiber imbedded in PLA (**a**) compared to a smoother fiber, where PLA did not cling well (**b**).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **SFUD** & **RFUD** & **SFUD** & **RFUD** & **PLA** \\  & **0\({}^{\circ}\)** & **0\({}^{\circ}\)** & **45\({}^{\circ}\)** & **45\({}^{\circ}\)** & **PLA** \\ \hline Tg (\({}^{\circ}\)C) & 59.06 & 59.38 & 57.16 & 59.07 & 61.16 \\ Tc (\({}^{\circ}\)C) & 126.44 & 129.13 & 121.48 & 124.99 & 126.52 \\ Tf (\({}^{\circ}\)C) & 153.23 & 152.92 & 150.74 & 152.23 & 153.35 \\ R (\%) & 14.1 & 9 & 26.1 & 19.6 & 0.7 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Condensed results of DSC tests on the different composite configurations investigated (SF: sorted fibers, RF: raw fibers).  
The sorting of fibers appears to be beneficial to the strength of the specimen, it increases from 4.51 for RF to 5.41 GPa (20% gain) for SF. Similar observations can be made regarding Young's modulus, with a value increasing from 44.07 for RF to 53.99 MPa on average (22.5% gain) for SF.  
Figure 11 shows that the specimen broke cleanly at both 0 and 45\({}^{\circ}\) (no delamination), which validates our intermediate plate technique used for specimen plate production. Similarly, no warping deformation (curvature of the plate after demolding) that may affect the outcome of the tensile test, was noted.  
As seen in Figure 11, the breakage occurred at different locations on each of the specimens, which indicates that the fibers are distributed sufficiently homogeneously so as not to create defects at the scale of the plate.