## 3 Results and Discussion
### Dma  
Figure 4 presents the storage modulus (\(E\)') and tangent delta (tan \(\delta\)) curves obtained from DMA both as function of temperature. Table 4 presents the values of \(T_{\mathrm{g}}\) obtained from each of the curves plotted in Figure 4. The thermomechanical response of the BVE and BVEL resins mostly present similar qualitative behavior, with some differences in the behavior immediately following the glass-transition process, which are discussed below (in this section). For both resins, the storage modulus showed a sigmoidal variation with  
Figure 3: GPC spectra of the two bio-based prepolymers (without and with lignin incorporation). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **BVE** & **BVEL** \\ \hline \(\mathrm{M_{n}}\) & 1555 & 1483 \\ \(\mathrm{M_{w}}\) & 2956 & 3561 \\ PDI & 1.9 & 2.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of GPC results. Figure 2: FTIR spectra of bio-based prepolymers, without and with lignin incorporation. increasing temperature, which was characterized by an initial plateau during the vitreous state, followed by a steep reduction due to the softening of the resin during the glass transition process; accordingly, this process is also correlated with the peaks of the tangent delta curves. The \(T_{\rm g}\) values obtained from the onset of \(E^{\prime}\) decay were relatively similar for the resins cured for 4 h at 100 \({}^{\circ}\)C (BVE-1,2 and BVEL-1,2), being in the 55-60 \({}^{\circ}\)C range; the \(T_{\rm g}\) estimates obtained from the tan \(\delta\) peak were in the range of 95-105 \({}^{\circ}\)C, with the BVEL samples at the higher end of this range. This slight performance improvement of the BVEL resin (reflected in higher \(T_{g}\) values) suggests that the incorporation of lignin somewhat reduced the polymer chain mobility compared to the reference resin. This was expected considering that lignin is a complex and heterogeneous natural polymer with a relatively high molecular weight and rather rigid aromatic segments and considering its effects on the molecular weight of the prepolymers as discussed for the GPC analysis. The magnitude of the tan \(\delta\) peaks for the two resins was also significantly different, being 5 to 10% higher in BVEL. This further suggests a more amorphous and heterogeneous (less crystalline) polymer structure in that resin compared to BVE. However, it is important to note that the BVEL-3 specimen, post-cured for 24 h at 110 \({}^{\circ}\)C, exhibited significantly higher \(T_{g}\) values, estimated both from the onset of \(E^{\prime}\) decay (79.7 \({}^{\circ}\)C) and tan \(\delta\) peak (145.7 \({}^{\circ}\)C); additionally, this specimen exhibited a sudden increase in \(E^{\prime}\) following the glass transition process, failing due to bending inside the DMA chamber shortly after. The peak of tan \(\delta\) occurred during this segment of the material's response, resulting in the unusual development of this curve; this should be taken into account when considering the \(T_{g}\) estimate taken from the tan \(\delta\) peak for this specimen. To further investigate this observation, the remaining BVEL samples were subjected to a second DMA run, during which similar post-glass-transition behavior (\(E^{\prime}\) increase