## 3 Results and Discussion
### FT-IR Spectra Results  
The FT-IR spectra of polyurethane and polyurethane-based biocomposites provide valuable information about their chemical structures and functional group interactions. Figure 8 shows the FTIR spectra of pure (without additive) and 2.5 wt.% HSO-reinforced polyurethane-based biocomposites. In the provided spectra, both pure polyurethane and the biocomposite exhibit characteristic peaks that correspond to various functional groups. The broad peak observed in the 3250-3450 cm\({}^{-1}\) range represents N-H stretching vibration, confirming the presence of urethane bonds (NH-COO). This peak also indicates hydrogen bonding interactions between hard segments in the polyurethane structure. Additionally, the peaks around 2850-3000 cm\({}^{-1}\) correspond to-CH group stretching vibrations from the alkyl groups present in the polymer backbone. These peaks are essential for identifying the core components involved in the polyurethane matrix. Further analysis of the spectra shows a strong peak around 1700-1720 cm\({}^{-1}\), attributed to C=O stretching vibrations from the urethane carbonyl groups. This peak serves as a primary indicator of urethane bond formation. In the spectra, the intensity of the carbonyl stretching peak can change depending on the interaction between hard segments (C=O groups) and hydrogen-bonded N-H groups, which influences the mechanical properties and thermal stability of the material. In addition, the C-O-C stretching vibrations in the range of 1100-1150 cm\({}^{-1}\), corresponding to the ether linkages from the polyol segments, are more pronounced in the spectra, suggesting modifications due to the incorporation of reinforcing agents. In polyurethane, the disappearance of isocyanate and hydroxyl group peaks indicates that the chemical reaction is proceeding efficiently. The absence of isocyanate peaks at wavelengths of 2250-2270 cm\({}^{-1}\) and a decrease in hydroxyl group absorbance around 3300-3600 cm\({}^{-1}\) confirm that the polymerization process is complete. This is an important indicator of successful synthesis and high reaction efficiency in polyurethane production.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Bulk density**} & \multicolumn{4}{c}{**Shore A hardness**} \\ \hline Std. Dev. & 0.1577 & R\({}^{2}\) & 0.9998 & Std. Dev. & 0.3191 & R\({}^{2}\) & 0.9941 \\ \hline Mean & 41.21 & Adjusted R\({}^{2}\) & 0.9996 & Mean & 9.36 & Adjusted R\({}^{2}\) & 0.9906 \\ \hline C.V. \% & 0.3828 & Predicted R\({}^{2}\) & 0.9987 & C.V. \% & 3.41 & Predicted R\({}^{2}\) & 0.9819 \\ \hline  & \multicolumn{2}{c}{Adeq Precision} & 198.7784 & \multicolumn{4}{c}{Adeq Precision} & 55.8053 \\ \hline  & \multicolumn{2}{c}{**Thermal conductivity**} & \multicolumn{4}{c}{**Dielectric constant**} \\ \hline Std. Dev. & 0.0001 & R\({}^{2}\) & 0.9971 & Std. Dev. & 0.0851 & R\({}^{2}\) & 0.9948 \\ \hline Mean & 0.0267 & Adjusted R\({}^{2}\) & 0.9934 & Mean & 6.01 & Adjusted R\({}^{2}\) & 0.9881 \\ \hline C.V. \% & 0.4640 & Predicted R\({}^{2}\) & 0.9764 & C.V. \% & 1.42 & Predicted R\({}^{2}\) & 0.9630 \\ \hline  & \multicolumn{2}{c}{Adeq Precision} & 53.3723 & \multicolumn{4}{c}{Adeq Precision} & 42.6100 \\ \hline  & \multicolumn{2}{c}{**Tensile strength**} & \multicolumn{4}{c}{**Strain**} \\ \hline Std. Dev. & 0.0314 & R\({}^{2}\) & 0.9896 & Std. Dev. & 4.47 & R\({}^{2}\) & 0.9980 \\ \hline Mean & 0.5571 & Adjusted R\({}^{2}\) & 0.9762 & Mean & 177.55 & Adjusted R\({}^{2}\) & 0.9955 \\ \hline C.V. \% & 5.64 & Predicted R\({}^{2}\) & 0.9229 & C.V. \% & 2.52 & Predicted R\({}^{2}\) & 0.9902 \\ \hline  & \multicolumn{2}{c}{Adeq Precision} & 27.9568 & \multicolumn{4}{c}{Adeq Precision} & 67.5148 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Statistical evaluation of experimental data and RSM model predictions.