## 3 Results and Discussion
### Thermo-Mechanical Properties
DMA was used to assess thermo-mechanical properties of the resins and composites studied. These results are summarized in Figure 9 and Table 2. At temperatures below 20 \({}^{\circ}\)C, the resin prepared with fatty acids displays a higher storage modulus than the resin prepared with tung oil triglycerides (Figure 9a,b), exhibiting a behavior that is reflective of the expected, more prevalent hydrogen bonding. Above 20 \({}^{\circ}\)C, it is believed that chain mobility overcomes hydrogen bonding, and that the more crosslinked structure of the resin prepared with tung oil accounts for the higher storage modulus observed in comparison to the resin prepared with fatty acids. At the rubbery plateau (\(T_{\mathrm{g}}+50\)\({}^{\circ}\)C), above all phase transitions of the materials, the storage modulus for the resin prepared with tung oil is approximately 4.7 times higher than that of the resin prepared with fatty acids (68.9 MPa vs. 14.6 MPa, respectively, Table 2). Indeed, that same trend is also clear in the calculated crosslink density, with \(16.2\times 10^{-4}\) mol/cm\({}^{3}\) for the fatty acid resin and 77.7 \(\times\) 10\({}^{-4}\) mol/cm\({}^{3}\) for the tung oil resin (Table 2). Cross-link densities were calculated based on the rubbery elasticity theory, according to Equation (1) [24; 25]:  
\[\mathrm{Crosslink\ density}=E^{\prime}/RT \tag{1}\]  
where \(E^{\prime}\) is the storage modulus at \(T_{\mathrm{g}}+50\)\({}^{\circ}\)C, R is the gas constant, and \(T\) is the absolute temperature (K). Crosslink density was not calculated for composites (Table 2) because the numbers would be artificially inflated by the natural increase in \(E^{\prime}\) resulting from the addition of a reinforcement, therefore masking the true crosslink density value. It is also worth noting that DMA specimens could not be produced from the resin prepared with methyl esters due to its exceeding fragility. In the presence of the cellulose reinforcement, the composite prepared with methyl esters exhibits significant lower storage modulus than the composite made from fatty acids (Figure 9d,e), indicating that a stronger reinforcing effect is obtained for the more polar resin, as expected due to its increased affinity with the reinforcement. For the composite prepared with tung oil triglyceride (Figure 9c), the storage modulus is consistently higher than all other composites, revealing that, contrary to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Major Resin Component** & **Reinforcement** & \(T_{\mathrm{g}}\) \({}^{\circ}\)C & \(E^{\prime}\) at 25 \({}^{\circ}\)C & \(E^{\prime}\) at \(T_{\mathrm{g}}+50\) & **Cross Link Density** \\  & & **(MPa)** & \({}^{\circ}\)C (MPa) & **(mm)** \\ \hline Tung oil & – & 30 & 338.4 & 68.9 & 77.7 \\ Fatty acid & – & 39 & 284.8 & 14.6 & 16.2 \\ Tung oil & \(\alpha\)-cellulose & 38 & 524.0 & 131.2 & – \\ Fatty acid & \(\alpha\)-cellulose & 56 & 459.5 & 31.7 & – \\ Methyl ester & \(\alpha\)-cellulose & \(-6\) & 20.2 & 11.8 & – \\ \hline \hline \end{tabular}  
\({}^{\mathrm{a}}\)\(T_{\mathrm{g}}\) was obtained from the peak of the tan\(\delta\) curve.  
\end{table} 
Table 2: DMA results for samples prepared with tung oil, tung oil fatty acids, and tung oil methyl esters. Figure 9: **(A)** Storage modulus (E’) vs. temperature and (**B**) tan \(\delta\) curves for (a) a resin prepared with tung oil, (b) a resin prepared with fatty acids, (c) a composite prepared with tung oil, (d) a composite prepared with fatty acids, and (e) a composite prepared with methyl esters. expected, the crosslink density of the resin is a greater contributor towards final mechanical properties than fiber-matrix interactions.