## 3 Results and Discussion
### Mechanical Properties
It should be noted that the sample reinforced with 10 wt% FFF has similar and even higher flexural mechanical properties than those obtained in commercial WPCs currently used in furniture applications [59; 60]. For higher FFF contents, it is observed that the flexural modulus decreases as the reinforcement content increases, obtaining the lowest modulus for the sample reinforced with 40 wt% FFF, 2108 MPa, which shows the same behavior above-mentioned. Regarding the impact energy (Charpy test), it can be seen in Table 1, that the incorporation of both CFF and FFF in the BioEP resin results in a remarkable decrease in impact-absorbed energy from 21.8 kJ m\({}^{-2}\) corresponding to the unfilled BioEP resin to values around 3 kJ m\({}^{-2}\) for FF reinforced composites. This behavior is typical of polymeric composites filled with lignocellulosic particles due \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Code**} & \multicolumn{2}{c}{**Flexural Properties**} & **Impact Energy** & **Hardness** \\ \cline{2-5}  & **FS (MPa)** & **E\({}_{\text{f}}\) (MPa)** & **(k) m\({}^{-2}\)** & **(Shore D)** \\ \hline BioEP & 95.2 \(\pm\) 3.4 & 2985 \(\pm\) 115 & 21.8 \(\pm\) 3.4 & 83.2 \(\pm\) 1.0 \\ BioEP\_10 CF & 40.4 \(\pm\) 1.3 & 2840 \(\pm\) 242 & 2.7 \(\pm\) 0.9 & 83.3 \(\pm\) 0.6 \\ BioEP\_20 CFF & 31.5 \(\pm\) 0.5 & 2878 \(\pm\) 86 & 2.6 \(\pm\) 0.6 & 82.3 \(\pm\) 1.0 \\ BioEP\_30 CFF & 28.0 \(\pm\) 2.0 & 2930 \(\pm\) 93 & 2.4 \(\pm\) 0.2 & 82.2 \(\pm\) 1.0 \\ BioEP\_40 CFF & 22.5 \(\pm\) 0.8 & 2290 \(\pm\) 127 & 2.2 \(\pm\) 0.3 & 81.0 \(\pm\) 1.0 \\ BioEP\_10 FFF & 50.2 \(\pm\) 1.4 & 3579 \(\pm\) 53 & 3.6 \(\pm\) 0.5 & 83.3 \(\pm\) 1.0 \\ BioEP\_20 FFF & 38.7 \(\pm\) 7.0 & 2975 \(\pm\) 84 & 3.4 \(\pm\) 0.1 & 83.7 \(\pm\) 0.5 \\ BioEP\_30 FFF & 31.8 \(\pm\) 1.5 & 2696 \(\pm\) 20 & 2.7 \(\pm\) 0.4 & 83.0 \(\pm\) 1.1 \\ BioEP\_40 FFF & 22.9 \(\pm\) 2.4 & 2108 \(\pm\) 204 & 2.4 \(\pm\) 0.2 & 81.6 \(\pm\) 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the main mechanical properties of BioEP and BioEP/FF composites reinforced with different content of coarse (CFF) and fine (FFF) flavseed flour particles obtained by flexural, impact, and hardness tests. to the lack of (or very poor) interfacial adhesion between the reinforcement and the matrix, which gives rise to stress concentration points, promoting the formation of microcracks at the interface when impact conditions are applied that easily induce crack propagation, thus decreasing their impact resistance [61; 62]. Impact energy absorption is also influenced by the filler content in the matrix. As can be seen, the impact energy absorption becomes lower as the reinforcement content increases, obtaining the lowest impact-absorbed energy for composites reinforced with 40 wt% CFF and FFF, with an impact energy of 2.2 and 2.4 kJ m\({}^{-2}\) respectively, which represents a decrease of nearly 90% in both cases with respect to the BioEP resin. This decrease in impact energy with the higher filler content is due to the greater lack of interaction between the filler and the matrix, which results in a higher void content, thus increasing the stress concentration phenomena. Particle size is another factor affecting the impact of energy absorption. When comparing the composites, the energy absorption values for the different percentages of reinforcement are slightly lower in the case of CFF-reinforced composites. This is because the coarse particles have less dispersion in the matrix as well as a larger surface area that leaves a greater amount of surface-exposed between the filler and the matrix, negatively affecting the mechanical properties [63]. It is worthy to note that the better results regarding mechanical properties, obtained with FFF were expected as the morphology of FFF is rounded (almost spherical in most cases) while CFF show very irregular shapes with angular geometries that contribute to micro crack formation and subsequent growth.