## 3 Results and Discussion  
### Starting Materials  
Tung oil and its corresponding fatty acids and methyl esters were analyzed by FTIR, \({}^{1}\)H NMR, and Raman spectroscopies, and by GC-MS in order to check for purity and to confirm the structure of the bio-based starting materials used for the preparation of polymers and composites in this work. When comparing the FTIR spectra of tung oil, isolated \(\upalpha\)-eleostearic acid, and tung oil methyl esters (Figure 1), it can be observed that the main structural features of the fatty acid chain in tung oil are unaltered after saponification and transesterification. Signals, such as the strong peak at approximately 1750 cm\({}^{-1}\), representing the carbonyl C=O stretch, and the strong peak at approximately 1000 cm\({}^{-1}\), which corresponds to the C-O stretch in the ester (tung oil and methyl esters) or carboxyl (\(\upalpha\)-eleostearic acid) functional groups, can be seen in all three spectra (Figure 1). Likewise, the peak at 990-980 cm\({}^{-1}\), representing the C-H wagging vibrations of conjugated carbon-carbon double bonds are also observed in all three compounds (Figure 1) [20]. It's interesting to note the absence of the typical signal for the O-H stretch in the spectrum of isolated \(\alpha\)-eleostearic acid (Figure 1). It is believed that, due to the basic reaction conditions employed during saponification, the final fatty acid is obtained in its salt form as a sodium carboxylate, which does not affect its subsequent polymerization and/or future interactions with the reinforcement. The \({}^{1}\)H NMR spectra of the bio-based starting materials (Figure 2) and the peak integration of their corresponding key signals provide further insight into reaction completion and product purity. The characteristic signals for the methylene (4.1-4.3 ppm, signal 6) and the methylene (\(\sim\)5.25 ppm, signal 7) hydrogens of the glycerol backbone can be clearly seen in the \({}^{1}\)H NMR spectrum of tung oil (Figure 2a). Their absence from the spectra of tung oil methyl esters and isolated \(\alpha\)-eleostearic acid (Figure 2b,c, respectively) confirms successful separation of any residual glycerol from the desired products. The intense singlet at 3.5 ppm in the spectrum of the tung oil methyl ester (Figure 2b) corresponds to its newly formed methyl group. The absence of such peak from the spectrum of isolated \(\alpha\)-eleostearic acid (Figure 2c) suggests successful synthesis, purification, and drying of the desired fatty acid. As explained previously, the fatty acid is obtained in its salt form, therefore, the proton of the carboxyl group isn't detected for the fatty acid. It is important to note that all peaks related to the fatty acid carbon backbone of tung oil (signals 1-5 and 8, Figure 2a) are virtually unchanged after either transesterification (Figure 2b), or saponification (Figure 2c), indicating that the carbon chain is intact, including the set of three naturally conjugated carbon-carbon double bonds. Indeed, the integration of vinylic hydrogens (5.3-6.4 ppm, signal 8) with respect to the terminal methyl group (\(\sim\)0.8 ppm, signal 1) in each spectrum confirms that the  
Figure 1: FTIR spectra of (**a**) tung oil methyl esters, (**b**) isolated \(\alpha\)-eleostearic acid, and (**c**) tung oil. Figure 2: \({}^{1}\)H NMR spectra of (**a**) tung oil, (**b**) tung oil methyl esters, and (**c**) \(\alpha\)-eleostearic acid. unsaturations were not affected by the reactions performed. In each case, the integration indicates a total of 6 vinylic hydrogens per fatty acid chain. Another indication that the unsaturations are not compromised by either transesterification or saponification of tung oil can be obtained by a quick analysis of the Raman spectra of the three samples (Figure 3). Indeed, the intense peak at approximately 1630 cm\({}^{-1}\), associated to C=C vibrations, is clearly observed in all three spectra (Figure 3). The purity of the bio-based starting materials was verified by GC-MS.