## 3 Results and Discussion
### Thermo-Mechanical Properties
It is interesting to note that at lower temperatures, the fatty acid resin (Figure 9b) exhibits higher storage modulus than the other systems, surpassing the tung oil resin (Figure 9a) below 24 \({}^{\circ}\)C as discussed previously, the fatty acid composite (Figure 9d) below 23 \({}^{\circ}\)C, and the tung oil composite (Figure 9c) below 3 \({}^{\circ}\)C. This trend indicates that below the \(T_{\rm g}\) of the polar resin, hydrogen bonding between the resin and reinforcement is limited, therefore, the ligno-cellulosic filler particles represent weak points within the sample, contributing to the lower mechanical performance observed at lower temperatures in comparison to the pure resin. For all samples investigated, the tans curves (Figure 9) exhibit a single major peak, representing the glass transition of the system evaluated. The presence of a single transition is indicative of a homogeneous polymer with no evident phase separation. It is worth noting that the use of vegetable oils with less carbon-carbon double bonds typically results in polymers with more than one \(T_{\rm g}\)[8; 9], and this behavior has been attributed to a micro-phase separation within the polymer network due to a significant difference in reactivity of the co-monomers used. The presence of a single tan\(\delta\) peak for the composite samples (Figure 9c-e) also suggests that cellulose fibers have been evenly distributed throughout the polymer, providing universal thermo-mechanical properties for the entire sample. Another indicator of resin heterogeneity is the breadth of the tan\(\delta\) peak. Indeed, the narrower the peak, the more homogeneous the system. It is interesting to notice how the addition of reinforcement changes the breadth of the tan\(\delta\) peak for the samples prepared with fatty acids (Figure 9b,d). The same effect is not observed for the other resins, therefore revealing greater interaction between resin and reinforcement on the composite prepared with fatty acids. Indeed, as observed previously in similar systems, a greater interaction of one of the resin components with the reinforcement contributes to composite heterogeneity at the molecular level [8]. The greater interaction between fatty acids and cellulose is also reflected in the \(T_{\rm g}\) values of the samples (Table 2). Indeed, there is only a small change in the \(T_{\rm g}\) of samples prepared with tung oil upon addition of cellulose, revealing that the presence of cellulose has little effect on the polymerization of the resin and its intrinsic properties. For the fatty acid resin, a significant increase of the \(T_{\rm g}\) from 39 to 56 \({}^{\circ}\)C (Table 2) is observed upon the addition of cellulose. This increase in \(T_{\rm g}\) suggests a stronger affinity between resin and reinforcement, resulting in more restricted chain mobility. Among all samples, the composite prepared with methyl esters exhibits the lowest \(T_{\rm g}\) (\(-6\)\({}^{\circ}\)C, Table 2), indicating the combination of a weak resin with a poor adhesion between the resin and reinforcement. Finally, the maximum value in the tan\(\delta\) curve (tan\(\delta_{\rm max}\)) can be associated to the damping properties of the material. It is noteworthy that all composites exhibit tan\(\delta_{\rm max}\) values lower than their corresponding unreinforced resins (Figure 9), with a more pronounced decrease (from approximately 0.44 to approximately 0.23, Figure 9b,d) for the fatty acid system. This greater decrease is most likely the result of limited ability of the composite in dispersing shock/sound waves into molecular/chain movements, due to the greater interaction between resin and reinforcement, effectively interlocking the polymer chains through hydrogen bonding. When comparing the different composites, it is clear that the sample prepared with methyl esters exhibits the highest tan\(\delta_{\rm max}\), which can be associated to a better ability to dampen vibration through dissipation of the energy into polymer chain movement.