## 3 Results and Discussion
### Morphological Properties  
The particle dispersion and its interaction with the matrix are two of the main aspects that influence the composite's mechanical properties. To study these phenomena, a morphological study was carried out using FESEM on impact fractured surfaces of BioEP resin and BioEP/FF composites filled with 10 wt% and 40 wt% CFF and FFF. Figure 5a shows the BioEP resin fracture surface, which is characterized by a smooth surface with the presence of cleavage planes characteristic of a brittle fracture.  
After the addition of 10 wt% of both CFF and FFF filler (Figure 5b,d), it can be seen that the fracture surface acquires a noticeable roughness, and small holes appear randomly located on the surface, which corresponds to the particles pulled out after the impact test. These voids/holes are representative of poor adhesion between the polymeric matrix and the lignocellulosic filler, which  
Figure 5: FESEM images at 500x of impact-fracture surface of: (**a**) BioEP; (**b**) BioEP_10 CFF; (**c**) BioEP_40 CFF; (**d**) BioEP_1 OFFF and (**e**) BioEP_40 FF.  
results, as above-mentioned, in low stresses transfer from the matrix to the filler, thus negatively affecting the overall mechanical properties of the obtained composites. Comparing the two types of composites reinforced with 10 wt% FF, it can be seen that fine particles (FFF) reinforced composites, a better particle dispersion in the matrix is achieved due to the smaller particle size, which is reflected in the absence of aggregates in the fracture surface. Such aggregates are observed on the fracture surface of the coarse particles (CFF) reinforced composites, as the larger particle size promotes their aggregation. The higher lack of adhesion between these aggregates and the matrix due to the increase of the exposed surface area intensifies the stress concentration phenomena that negatively affects the mechanical properties, as it has been evidenced by a lower impact energy absorption and lower flexural strength than the composite reinforced with 10 wt% FFF. Higher filler contents (Figure 5c,e) lead to an increase in the fracture surface roughness with the presence of particles embedded in the matrix. An increase in the size of the voids/holes was also observed, possibly because the higher filler content promoted aggregate formation. This increase in the void size results in reduced interfacial adhesion between the reinforcement and the matrix for composites reinforced with high FF contents, which is reflected in poor mechanical properties. Comparing both composites reinforced with 40 wt% of FF, the presence of large aggregates in the CFF reinforced sample can be seen more clearly, while in the FFF reinforced sample, the dispersion of particles was more homogeneous. Therefore, the increase of the filler content in the matrix results in a significant decrease in ductile and resistant mechanical properties, as shown by the evolution of impact energy absorption and flexural strength, due to a reduction in interfacial adhesion between filler and matrix by a decrease in the resin's ability to fully embed the particles. This also occurs with coarse particles (CFF), which have a higher surface area, exposing more surface area to weak bonding with the matrix, resulting in lower flexural strength and higher water absorption capacity.