## 4 Results and Discussion  
The addition of fibers to the PLA matrix leads to an increase in longitudinal elastic modulus, accompanied by a slight decrease in tensile strength and elongation at break (Table 4). The fracture occurs perpendicular to the fibers so that the fracture profiles in the specimens with 45\({}^{\circ}\) fibers are also inclined at 45\({}^{\circ}\). In addition, a two-step fracture can be shown, firstly with the matrix and then on the fibers. Moreover, it has also been shown that fiber alignment plays a minor role in the mechanical performance of the specimens, with the 45\({}^{\circ}\) oriented sorted fibers participating less in the strengthening than the 45\({}^{\circ}\) oriented raw fibers. Although the standard deviations do not really allow for differentiation of the two plate types, it seems that the use of raw  
Figure 11: Tensile test on sorted fibers oriented 0\({}^{\circ}\) (**right**) and 45\({}^{\circ}\) (**left**); for a traverse speed of 1 mm/min and 20 mm/min. Figure 10: Tensile curves obtained for 5 sorted fibers specimens with a fiber orientation of 0\({}^{\circ}\) and for a test performed at a speed of 1 mm/min. fibers at 45\({}^{\circ}\) brings a greater resistance compared to the use of sorted fibers. This result could be due to the fact that the greater disorganization creates reinforcements in a wider angular range which takes part in the load transport. If we add to this the fact that a large part of the mechanical strength comes from the matrix for a 45\({}^{\circ}\) UD composite, it is normal to see better results for the raw fibers. We can already assume that the same will be true for a 90\({}^{\circ}\) fiber orientation. Since the tensile modulus of the fibers oriented at 45\({}^{\circ}\) can also be seen as the shear modulus of the composite, we can retain a value of 3.99 GPa for this shear modulus. Furthermore, failure occurs around a 1.24% strain at best (Table 4), whereas the elongation at break of both PLA and fibers lie above 2%. This loss of strain of the composite compared to the two components alone may be caused by the heating process that weakened the structure of the fibers or caused by poor point adhesion between the fibers and the matrix creating local de-cohesions with excessive load transfer to the PLA matrix. As a matter of fact, we noted (Figure 4) the presence of wax or sap residues visible on the surface of some fibers used. These residues can affect the proper transmission of forces between the fibers and the matrix because the mechanical fiber/matrix anchoring depends on the roughness, the wettability of the fibers [22] as well as the chemical affinity (polarity) with the matrix. To improve this bonding, chemical treatments (NaOH, etc. ), have been used [14; 34; 35; 38] to clean the fiber and can, in some cases, significantly improve the performance. The choice to use chemical treatment can also, in some cases, weaken the fiber. However, above all, the biocompatible thus treated loses its 100% bio-sourced aspect, which we do not want here. The fiber ratio used in this work was 10%. It constitutes a preliminary approach to visualizing the properties of the PLA/nettle composite. Tests at 20, 30, and 40% (by mass) are in progress. The presence of a higher fibers ratio does not necessarily seem to be advantageous for the composite mechanical properties because the fibers' embedding in PLA is not optimal, the fibers tend to agglomerate together in bundles. This creates porosities that lead to a non-linear evolution of the mechanical properties and progressive embrittlement of the composite [39; 40; 41]. This porosity phenomenon is also the reason for our change in the manufacturing process of the plates. Indeed, prior to the procedure depicted in Figure 6, a selected mass ratio of fibers and PLA pellets were placed on different layers (sandwich method), directly in a mold to produce the plates for the tensile specimens.