## 3 Results
### Activation Energy  
Figure 2 illustrates the effects of SSP, EPA, and EPB contents on the thermal degradation behavior of the composites. In the SSP-EPA interaction, increasing EPA content at both low and high SSP levels negatively affects thermal stability. This is due to insufficient reinforcement at low SSP levels and stress concentrations at high SSP levels. In the SSP-EPB interaction, increasing EPB content enhances thermal stability at low SSP levels; however, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Source** & **Sum of Squares** & **Mean Square** & **F-Value** & _p-Value_ \\ \hline Model & 0.2477 & 0.0275 & 105.94 & \textless{}0.0001 \\ A-SSP (g) & 0.0865 & 0.0865 & 333.15 & \textless{}0.0001 \\ B-EPA (g) & 0.0018 & 0.0018 & 6.88 & 0.0342 \\ C-EPB (g) & 0.0041 & 0.0041 & 15.96 & 0.0052 \\ AB & 0.0000 & 0.0000 & 0.1737 & 0.6893 \\ AC & 0.0001 & 0.0001 & 0.4625 & 0.5183 \\ BC & 0.0004 & 0.0004 & 1.46 & 0.2668 \\ A\({}^{2}\) & 0.1466 & 0.1466 & 564.24 & \textless{}0.0001 \\ B\({}^{2}\) & 0.0135 & 0.0135 & 51.91 & 0.0002 \\ C\({}^{2}\) & 0.0394 & 0.0394 & 151.54 & \textless{}0.0001 \\ Residual & 0.0018 & 0.0003 & & \\ Lack of Fit & 0.0015 & 0.0003 & 1.96 & 0.3719 \\ Pure Error & 0.0003 & 0.0002 & & \\ Cor Total & 0.2495 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: ANOVA analysis for Charpy impact tests of the bio-composites. Figure 1: (**a**) Effects of EPA and SSP contents, (**b**) effects of EPB and SSP contents, and (**c**) effects of EPA and EPB contents on Charpy impact test. this effect becomes limited at higher SSP content. While EPB is known to improve heat resistance by increasing polymer network rigidity, this benefit is reduced when excessive SSP disrupts matrix homogeneity. The EPA-EPB interaction shows maximum thermal stability when both components are present at balanced levels. The activation energy achieves its highest values when EPA is at a minimum and EPB is at a maximum, with a similar trend observed under reverse conditions, suggesting a dual stability point. These results show that filler distribution, crosslink density, and interfacial interactions directly influence thermal stability. The optimal balance of these components is therefore critical for enhancing the composite's thermal resistance. The quadratic model proposed by the RSM design for activation energy prediction is presented in Equation (4). These results can be explained by SSP acting as a bio-filler that raises the decomposition energy through physical barrier effects, improved filler-matrix bonding, and reduced mobility of volatile degradation products. Optimal SSP ratios promote uniform dispersion and strong interfacial adhesion, delaying thermal decomposition, while excessive loading may cause agglomeration or voids that reduce barrier effectiveness. Reported activation energy values for composites using mineral fillers such as calcium carbonate typically range from 120 to 160 kJ/mol [15], while bio-fillers like eggshell and snail shell powders show comparable improvements in thermal stability [13; 14], supporting the suitability of SSP as a sustainable filler in enhancing thermal resistance. \[ \begin{split}\text{Activation Energy (kJ/mol) = 118.09686 - 2.67045 \times SSP + 1.87477 \times EPA + 6.38928}\\ \times\text{EPB}-7.41963\times 10^{-15}\times SSP\times\text{ EPA}-1.62136\times 10^{-14}\times SSP\times\text{EPB}-2.41015 \times 10^{-14}\\ \times\text{EPA}\times\text{EPB}+2.06204\times(\text{SSP})^{2}-0.046353 \times(\text{EPA})^{2}-0.182602\times(\text{EPB})^{2}\end{split}  \tag{4}\]  
Table 3 confirms that the model is statistically significant (\(p<0.0001\)) and that SSP, EPA, and EPB contents have notable effects on the activation energy. SSP (A) exhibits the strongest influence (F = 1104.95, \(p<0.0001\)), followed by EPA (B) (F = 57.44, \(p=0.0001\)) and EPB (C) (F = 14.37, \(p=0.0068\)).