## 3 Results and Discussion
### Thermo-Mechanical Properties  
The thermogravimetric analysis (TGA) of tung oil, tung oil fatty acid, and tung oil methyl ester resins (Figure 8a-c) shows a clear trend for their thermal stability. It is indeed obvious that the onset degradation temperature (\(T_{\text{onset}}\)) for the tung oil methyl ester resin (\(\sim\)100 \({}^{\circ}\)C) is much lower than that of samples prepared with tung oil fatty acids (\(\sim\)180 \({}^{\circ}\)C) or tung oil triglycerides (\(\sim\)300 \({}^{\circ}\)C). This trend can be explained as a consequence of the chemical structure of the major resin components. For example, the markedly higher \(T_{\text{onset}}\) observed for the tung oil resin is the result of a highly crosslinked structure, due to the fact that the tung oil triglyceride monomer consists of three fatty acid esters connected to a glycerol backbone. In both fatty acids and methyl esters, the polymerizable fatty chains are independent from each other, resulting in a much less crosslinked polymer network. The difference observed in the \(T_{\text{onset}}\) of fatty acid and methyl ester polymers can be associated to their polarity. The polar fatty acid resin exhibits stronger hydrogen bonding interactions between polymer chains, resulting in a more compact arrangement of the overall polymer structure and, therefore, constituting a more thermally stable material in comparison to its methyl ester analogue. It is also apparent, from the TGA results (Figure 8a-c), that the bulk of the thermal degradation process occurs from \(T_{\text{onset}}\) to approximately 480 \({}^{\circ}\)C for the resins prepared with tung oil and methyl esters (Figure 8a,c), while the resin prepared with fatty acids clearly exhibits an additional secondary step starting at approximately 450 \({}^{\circ}\)C (Figure 8b). The major degradation process is believed to correspond to the breakdown of the cross-link network of the thermoset. The additional degradation step observed for the resin prepared with fatty acids could be associated to the final oxidation of residues and char formation, but its definitive origin can't be reliably inferred from the TGA results alone, lying outside the scope of the work described in this manuscript. A very similar trend in thermal stability can be observed for the composites (Figure 8d-f) compared to their corresponding resins (Figure 8a-c). All composites exhibit a very clear thermal degradation profile, with two distinct stages that can be associated with the degradation of the resin and the degradation of the reinforcement, although it is unavoidable that the degradation of these two components (resin and reinforcement) occur with some overlap. When correlating the results observed with fiber-matrix interactions, one would expect that a stronger binding between resin and reinforcement would result in a better fiber protection, and ultimately in a delayed degradation, especially towards the end of the thermal degradation process. Indeed, when comparing the temperature at 80 wt % degradation (\(T_{80}\)) for resins and their corresponding composites, respectively, an increase from \(\sim\)430 to -450 \({}^{\circ}\)C can be seen for samples prepared with fatty acids, whereas a decrease from \(\sim\)445 to \(\sim\)425 \({}^{\circ}\)C is observed for samples prepared with methyl esters. This behavior is reflective of the better fiber-matrix interactions obtained with fatty acids in comparison to methyl esters. In the case of tung oil triglyceride, the increase in \(T_{80}\) from \(\sim\)455 to \(\sim\)475 \({}^{\circ}\)C, for resin and composite, respectively, can be associated to the  
Figure 8: TGA curves of (**a**) tung oil resin, (**b**) tung oil fatty acid resin, (**c**) tung oil methyl ester resin, (**d**) composite prepared with tung oil resin, (**e**) composite prepared with tung oil fatty acid resin, and (**f**) composite prepared with tung oil methyl ester resin. highly crosslinked structure of the oil offering thermal protection to the fiber despite the expected poor fiber-matrix interaction.