## 3 Results and Discussion
### IFR Bioadditive Characterization
This effect, together with LS as a crosslinker, would explain the increased stiffness observed in the formulations. Thus, the highest magnitude value of E', of the composite material (wood-bioadditive-wood) is concurrent with the highest concentrations of magnesium hydroxide in the IFR product formulations. Dynamic mechanical analysis (DMA) not only made it possible to determine the stiffness of the wood-bioadditive-wood bond but also facilitated the definition of a pressing cycle to evaluate the adhesion properties of the PVAc-bioadditive IFR adhesive blends on veneer bonds. Regarding the shear strength results, the strength values ranged from 0.95 to 1.14 MPa, where formulation F2 presented the highest value. In general, it was observed that the shear strength increased by the higher concentration of Mg(OH)\({}_{2}\). Magnesium hydroxide has been used as a filler in PVAc adhesives for wood, improving its mechanical strength and fire-retardant properties. In shear tests, a concentration of 7.5 phr showed the highest strength (1140 N), outperforming pure PVAc adhesive (1027 N), and with Mg(OH)\({}_{2}\) acting \begin{table}
\begin{tabular}{c c c c} \hline
**Test** & **Property** & **F1** & **F2** \\ \hline \multirow{3}{*}{DMA} & E’ Maximum (Pa) Average & 2.041 \(\times\) 10\({}^{9}\) \(\pm\) 6.69 \(\times\) 10\({}^{7}\) & 2.398 \(\times\) 10\({}^{9}\) \(\pm\) 9.21 \(\times\) 10\({}^{7}\) \\ \cline{2-4}  & T (’C) E’ Maximum Average & 122.57 \(\pm\) 0.41 & 164.67 \(\pm\) 1.15 \\ \hline Shear test & Shear strength (MPa) & 0.95 \({}^{\text{b}}\)\(\pm\) 0.11 & 1.14 \({}^{\text{c}}\)\(\pm\) 0.15 \\ \hline \multirow{3}{*}{Fire resistance test} & Mass loss (\%) (ML) & 7.52 \({}^{\text{a}}\)\(\pm\) 0.66 & 10.72 \({}^{\text{a}}\)\(\pm\) 1.44 \\ \cline{2-4}  & Carbonization index (\%) (CI) & 3.44 \({}^{\text{a}}\)\(\pm\) 0.89 & 4.46 \({}^{\text{a}}\)\(\pm\) 1.94 \\ \hline \multirow{6}{*}{Fire resistance test} & The results correspond to the mean \(\pm\) St. Dev. a\({}^{\text{b,c}}\) reflects statistically significant differences, according to LSD test with 95% confidence interval (no statistically significant differences between levels sharing the same column or letter). Statgraphics Centuron XVII 19-X 64 software. \\ \cline{1-1} \cline{2-4}  & & \\ \end{tabular}
\end{table} 
Table 4: Characterization of IFR bioadditive formulations: dynamic mechanical analysis (DMA), shear test, and fire resistance test. as a reinforcing filler. However, at 10 phr, the shear strength decreased [62]. The synergy between magnesium hydroxide and lignocellulosic, with sulfonate and methoxyl groups, enhances the interaction with the adhesive matrix of protein and wood, favoring the formation of cross-linked structures and strong adhesive bonds through hydrogen bridges due to their polarity [1]. In addition, all the joints manufactured with the PVAc-bioadditive IFR adhesive blends presented results of shear strength above the maximum failure requirement value of 0.6 MPa (Table 1), which gives a good clue about the adhesion properties of the product with the wood. Fire retardancy tests were performed on wood specimens coated with each formulation, in which differences in weight and carbonization of each sample are not significant, since the fire tests did not show statistical variations between the ML and CI indicators in treated wood. However, differences were observed concerning untreated wood, showing that the IFR bioadditive slows combustion (Figure 2). Therefore, both formulations act favorably as passive fire protection products. The presence of the components of the formulations would be acting complementarily, thus, the proteins provide their intrinsic intumescence properties [31; 34], magnesium hydroxide, endothermic dehydration that cools the substrate surface [41], and LS contribute to the formation of significant volumes of carbon at high temperatures, coming from the abundant aromatic compounds in its structure [63].