## 4 Conclusions  
This paper investigated the effects of the incorporation of Kraft lignin obtained through the Lignoboost process from Eucalyptus wood on a partially bio-based vinyl ester (VE) resin. The study focused on the impacts of such an incorporation on the short-term mechanical properties (tensile and shear) and thermomechanical properties (i.e., glass transition and decomposition temperatures) of the base resin. The incorporation of 4% wt. of lignin resulted in a more amorphous (less crystalline) and heterogenous polymer chain with reduced mobility due to lignin's relatively complex and high molecular weight aromatic structure. In practical terms, this was reflected in the improvement of the mechanical and thermomechanical properties of the base resin: the tensile strength increased 27% and the shear strength increased 4%; an improvement was also observed for the glass transition temperature (defined based on the tan \(\delta\) peak), which increased from the 95-98 \({}^{\circ}\)C range to the 102-107 \({}^{\circ}\)C range. The VE resin with lignin incorporation also evidenced significant potential for additional cross-linking, even after a post-cure of 4 h at 100 \({}^{\circ}\)C. On the other hand, the resin with lignin incorporation showed a somewhat increased scatter in its mechanical response, particularly at higher stress levels, as well as higher brittleness. The tensile and shear moduli and the decomposition temperature were fairly similar to those of the reference resin without lignin. Overall, these results demonstrate that, despite requiring curing at high temperature, a minor incorporation of lignin can significantly improve the thermomechanical and mechanical behavior of bio-based VE resin. These results seem to confirm the promising potential of \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Resin**} & \multirow{2}{*}{**Specimen**} & **Shear Strength** & **Shear Modulus** & **Ultimate** \\  & & **(MPa)** & **(GPa)** & **Distortion (\%)** \\ \hline \multirow{8}{*}{BVE} & 1 & 49.6 & 1.37 & 4.31 \\  & 2 & 47.2 & 1.51 & 5.65 \\  & 3 & 48.2 & 1.57 & 6.19 \\  & 4 & 47.8 & 1.45 & 5.67 \\  & 5 & 57.4 & 1.67 & 6.61 \\ \cline{2-5}  & \multirow{2}{*}{Average} & \(50.0\pm 4.2\) & \(1.51\pm 0.11\) & 5.69 \(\pm\) 0.87 \\  & & (CoV = 8\%) & (CoV = 8\%) & (CoV = 15\%) \\ \hline \multirow{8}{*}{BVEL} & 1 & 52.1 & 1.51 & 6.41 \\  & 2 & 47.5 & 1.68 & 5.02 \\ \cline{1-1}  & 3 & 56.3 & 1.86 & 6.27 \\ \cline{1-1} \cline{2-5}  & \multirow{2}{*}{Average} & \(52.0\pm 4.4\) & \(1.68\pm 0.18\) & 5.90 \(\pm\) 0.77 \\ \cline{1-1}  & & (CoV = 8\%) & (CoV = 10\%) & (CoV = 13\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Shear test results (average \(\pm\) standard deviation and coefficient of variation (CoV)). Figure 7: Shear test results: shear stress vs. distortion curves obtained for (**a**) BVE and (**b**) BVEL resins. using this sustainable biopolymer in high-performance composite applications. However, the further assessment of the influence of lignin incorporation fraction on the properties of the resulting resins as well as their compatibility with typical fiber reinforcements are still necessary. Conceptualization. J.C.B., M.M. and M.H. ; methodology. [PERSON], M.H., M.M. and M.G. ; investigation. M.M., M.H., M.G., J.R.C., J.C.B. and I.C.R. ; resources. J.R.C. and M.G. ; data curation. M.M. ; writing--original draft preparation. I.C.R. and M.M. ; writing--review and editing. I.C.R., M.M., M.H., M.G., J.C.B. and J.R.C. ; visualization. M.M. and I.C.R. ; supervision. M.G., J.R.C. and J.C.B. ; project administration. M.G. and J.R.C. ; funding acquisition. M.G. and J.R.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the Portuguese National Innovation Agency (ANI) and Portuguese Foundation for Science and Technology (FCT) through projects _BioLam_ (POCI-01-0247-FEDER-039769-LISBOA 01-0247-FEDER-039769) and _EcoComposite_ (PTDC/ECI-EGC/29597/2017), respectively.