## 3 Results and Discussion
### Water Uptake Properties  
Figure 7 shows the evolution of the water absorption over time for BioEP resin and BioEP/FF composites filled with 10 wt% and 40 wt% of CFF and FFF. The water diffusion in the wood plastic composites is based on three different mechanisms, the first one involves the water molecules diffusion inside the micro-voids of the polymeric chains, the second mechanism is based on the water absorption by capillarity inside the voids and defects present at the matrix-filler interface, finally, the third mechanism involves the transport through the micro cracks that appear from the swelling of the fillers, namely, the swelling of the reinforcement produced by the contact with the water gives rise to the appearance of microcracks in the fragile thermosetting resin, which facilitates its penetration in the interface between the filler and the matrix [74]. As can be seen in Figure 7, the addition of FF into the BioEP resin significantly increased its water absorption capacity, which rose as the reinforcement content in the matrix increased. This could be due to two possible reasons, one of them is to the hydrophilic nature of the lignocellulosic filler, since cellulose and hemicellulose contain hydroxyl (-OH) groups in their structure that can easily interact with water molecules through hydrogen bonding, thus allowing a path for water entering [61; 75]. The other reason is the presence of small voids, pores and microcracks in the internal structure due to the lack of interfacial interaction between the filler and matrix and to the filler swelling. that facilitates the water accumulation in the composite by capillarity [24; 76]. By observing the water absorption curves of BioEP/FF composites, two stages can be clearly differentiated. We can see an initial stage with rapid water absorption, followed by a second stage where the curve stabilized into an asymptotic value, thus indicating saturation. Therefore, the water absorption of BioEP/FF composites followed Fickian's diffusion behavior. However, at low immersion times, Figure 7a, it can be seen how the weight gain in the curves of the composites stops being gradual and a rapid increase in weight appears between 10 and 12 h of immersion in all of them. This can be due to the appearance of deformations or damage to the matrix for that immersion time, such as the appearance of microcracks due to the swelling of the filler or the fiber/matrix debonding [77]. As shown in Table 4, the water saturation of composites increases as the filler content does. In this case, it can be seen how the water saturation of composites reinforced with 10 wt% of FF (both CFF and FFF) reaches values of 4.8 wt%. Obviously, composites with 40 wt% of FF water saturation are located at about 12.5 wt%, which means an increase in water absorption compared to neat BioEP resin of 114.3% and 458% respectively. A comparison of the two types of composites obtained shows that CFF-reinforced composites have a slightly higher water absorption compared to their FFF counterparts. This may be due to the larger particle size of the CFF filler, which results in less interaction with the matrix, producing a higher number of voids within the structure of composites. These voids allow the accumulation of water at the interface between the particle and the matrix thus increasing the absorption capacity of the composites [78]. In addition, the increased contact between FF particles as their size and content in the matrix increases contributes to water absorption by capillarity due to the creation of a percolating path through the filler network [79]. It should be noted that the water  
absorption of FF waste is lower than that obtained from other agroforestry waste that has been used in similar amounts as reinforcements in thermosetting polymeric matrices, such as peanut shells [63] or palm kernel shell [80]. As can be seen in Figure 7, there are some slight differences between the sort-term behavior (first 24 h, Figure 7a) and the long-term behavior (90 days immersion, Figure 7b).