## 2 Materials and Methods
### Design and Characterization of the Intumesent Fire-Retardant Yeast-Protein Bioadditive
#### 2.1.3 Mechanical and Thermal Characterization  
To study the interaction between the bioadditive and the substrate, Dynamic Mechanical Analysis (DMA) was performed through a \"three-point bending test\" on small-laminated wood specimens, 20 mm long, 5 mm wide, and 1.1 mm thick, bonded with each of the formulations, following the method used in the investigation of [PERSON] et al., 2024 [1]. Three measurements of each property were performed for each IFR bioadditive formulation. Complementarily, the bioadditive formulations were evaluated for their adhesion properties with wood, a relevant property, since it determines the adhesive capacity of the bioadditive and the substrate, as well as its potential compatibility in interactions with the commercial adhesive PVAc. A shear strength test was performed according to ASTM D2339 [47], in specimens with dimensions of 175 mm length, 25 mm width, and 3.2 mm thick, using an Instron universal testing machine. The pressing cycle to achieve adhesion of the veneers through the bioadditive was defined at 12 bar pressures for 6 min at a temperature of 160 \({}^{\circ}\)C, with an adhesive grammage of 220 g/m\({}^{2}\) according to [PERSON] et al., 2016 [20]. The temperatures obtained from the DMA allowed for the establishment of this pressing cycle. Ten specimens were tested for each IFR bioadditive formulation. According to the requirements of EN 314-1 [48], in the shear strength of veneers (Table 1) values greater than 1.0 MPa do not need a wood failure requirement due to wood tearing, which concerns the joint. The fire performance of wood pieces coated with the IFR bioadditive formulations was carried out with a volume of 250 mL of each bioadditive formulation. Thus, the fire evaluation was performed on 6 wood pieces for each formulation and 6 standard pieces of natural untreated wood of _Pinus radiata_ D. DON with dimensions of 310 mm length, 125 mm width, and 10 mm thick, completely covered by each formulation. Fire resistance tests were carried out according to ASTM D1360-98 (2011) [49]. The fire resistance test evaluation indicators were defined as carbonization index (%) (Equation (1)) and mass loss (%) (Equation (2)) determined from the tested specimens [50]:  
\[\mathrm{CI}=((\mathrm{I_{max}}\times\alpha_{\mathrm{max}}\times\mathrm{ec})/ \mathrm{V_{j}})\times 100, \tag{1}\]  
where CI corresponds to the carbonization index (%); \(\mathrm{I_{max}}\) corresponds to the maximum length of surface carbonization; \(\alpha_{\mathrm{max}}\) corresponds to the maximum width of surface char \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Requirements**} \\ \hline
**Mean Shear Strength fv (MPa)** & **Mean Apparent Cohesive Wood Failure (\%)** \\ \hline \(0.2\leq\mathrm{fv}<0.4\) & \(\geq\)80 \\ \(0.4\leq\mathrm{fv}<0.6\) & \(\geq\)60 \\ \(0.6\leq\mathrm{fv}<1.0\) & \(\geq\)40 \\ \(1.0\leq\mathrm{fv}\) & No requirement \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Requirement of shear strength and failure values for veneer joints. ring; ec corresponds to the carbonized thickness; V\({}_{\rm i}\) corresponds to the initial volume of the specimen (mm\({}^{3}\)). \[\rm{ML}=((P_{\rm{at}}-P_{\rm{dt}})/P_{\rm{at}})\times 100, \tag{2}\]  
where ML corresponds to the mass loss (%); P\({}_{\rm{at}}\) corresponds to the weight of the specimen before treatment; P\({}_{\rm{dt}}\) corresponds to the weight of the specimen after treatment. 1.4 Thermal Characterization by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC)  
* Thermogravimetric Analysis (TGA)  
The thermogravimetric analysis tests were performed on a Thermal Gravimetric Analyzer (TGA), TA Instruments (TGA), model Q50, located at the Centro de Polimeros Avanzados (CIPA Chile), Concepcion, Chile. The test consisted of analyzing the behavior and thermal stability of samples to determine the degradation temperatures and number of residues generated through the Universal Analysis 2000 software.