## 3 Results and Discussion
### Roughness  
Using a \"NANOVEA\" Optical Profilometer mod. PS50 (Sensibility 2 \(\upmu\)m, height range 25 mm, sampling length 2.5 mm, measuring speed of 0.5 mm/s), experimental measurements were carried out to evaluate average roughness (R\({}_{\text{a}}\)) of Bio-plastic compounds. The average roughness of Bio-plastic compounds was evaluated in flat surfaces (without taking into account \"staircase\" or \"stair-stepping\" problems) printed parallel (par) to the printing area while printed orthogonal (ort) to the printing area in flat surfaces. The printing parameters used are shown in Table 4. Bio-plastic compounds result in a better surface finishing compared to both ABS and PLA (Figure 3). HEMP bio-plastic compounds was the roughest of the \"new materials\" with a value very close to that of pristine PLA. The others Bio-plastic compounds have better finishes than both the Acrilonitrile-butadiene-stirene (ABS), and Polylactic acid (PLA) (Figure 4). Differently, the CAROB has a better finishing value. \begin{table}
\begin{tabular}{c c} \hline Layer height (mm) & 0.25 \\ \hline Infill ratio (\%) & 50 \\ \hline Nozzle diameter (mm) & 0.6 \\ \hline Printing speed (mm/s) & 60 \\ \hline Printing temperature (\({}^{\circ}\)C) & 200 \\ \hline \end{tabular}
\end{table} 
Table 4: Printing parameters. Figure 3: R\({}_{\text{a}}\) of new composites in comparison with pristine polylactic acid (PLA) and acrilonitrile-butadiene-stirene (ABS). Moreover, in Table 5, we also report the main mechanical properties of ABS, which constitutes a traditional synthetic polymer commonly used for Fused Deposition Modelling (FDM) 3D-printing [27; 28] in comparison with bio-based ones, such as PLA and our composite materials. More details on the results are given in the following. * HEMP (Hempt fillers 20%): this material has excellent tensile strength, thanks to the high presence of silicon contained in the hemp shives. This is a result not obtainable even with hemp fiber or wood sawdust. The elastic modulus is more than double if compared to ABS (+115%) and PLA (+133%). Moreover, the yield strength remains almost constant in comparison with ABS, but it increases significantly when compared to PLA (+16%) (see Figure 5). * WEED (Powder from hemp leaf fillers 20%): again, it results in a relevant increment of the elastic modulus. However, both yield stress and ultimate stress are smaller than ABS and PLA. In addition, this material undergoes a very high plastic deformation. This is due to cannabinoids, which give much plasticity to the material. The starting ABS or PLA have a percentage of elongation at break equal to about 3% [25]. Adding 20% of hemp leaf powder, this percentage reaches about 9%. * TOMATO (Cherry tomatoes fillers 20%): the performances in terms of ultimate stress and ultimate elongation are very similar to pristine PLA and ABS. However, the TOMATO elastic modulus is about +20% higher than ABS and PLA. Moreover, ABS shows a higher yield stress (about +30%) compared to the TOMATO composite. * CAROB (Carob flour fillers 20%): due to the high temperatures of the die, contained sugar becomes caramel, which gives the final material a noticeable elongation approaching the yield point. In fact, although most of its mechanical properties are similar to ABS and PLA, CAROB has a percentage of elongation at break which reaches more than a 20% value due to the addition of carob flour. Figure 5: Elastic modulus (up) and Yield stress (down) for PLA and filled materials. PRUNED (Orange pruning fillers 20%): material has shown excellent resistance to plastic deformation and failure compared to PLA (+25% and +42%, respectively) while the elastic modulus is similar. In this case, its mechanical properties are very comparable to ABS with the exception of yield elongation that is closer to PLA values. With reference to the visual/outer appearance, each filler produces peculiar characteristics. * HEMP: filler gives excellent surface touch properties, breathability, and wood effect (Figure 4c).