## 3 Results and Discussion
### Composites Characterization
#### 3.2.5 Mechanical Characteristics  
The incorporation of particulate fillers can modify the mechanical properties of polymers in many ways depending on the particle size, loading, particle-matrix interfacial adhesion, and the composites microstructure [37]. Similarly, the maximum strength sustained by composites under uniaxial tensile loading depends on the effective stress transfer between the matrix and fillers [38]. The results of stress-strain curve of the BC/PP composites are shown in Figure 8. It can be observed that the addition of BC considerably affects the deformation behavior of the composites compared to the neat PP. The PP demonstrates a typical yielding process and ductile nature followed by strain hardening at the low strain rate. Contrarily, BC/PP composites exhibit a quasi-brittle behavior under tensile deformation. In other words, neat PP shows highly ductile fracturing behavior, while the ductility of BC/PP composites decreases considerably. The inset image in Figure 8 shows that the composites' deformation to rupture decreases with increased pyrolysis temperature, except for BC300/PP composite sample. The area under the stress-strain curve, which represents the amount of energy that the material can absorb until rupture, decreased compared to the neat PP. The tensile modulus and strength of the neat PP and BC/PP composites are illustrated in Figure 9 and their numerical values along with their statistical significance analysis are summarized Table S2 (see the Supplementary Materials). It can be noticed that incorporation of the biochar into the polypropylene matrix leads to an increase in composites stiffness. This improved stiffness is due to the fact that the BC particles leads to hindered molecular mobility of the PP chain segments. The modulus of elasticity of the composites was found to increases gradually with pyrolysis temperature. It has been shown that the biochar derived from different sources has increased hardness and modulus at higher  
Figure 7: DSC of BC/PP composites: (**a**) Melting and (**b**) crystallization curve. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{5}{c}{**DSC Parameters**} \\ \cline{2-6}  & \(\mathbf{T_{c}}\) (\({}^{\circ}\)C) & \(\mathbf{\Delta H_{c}}\) (\(\mathbf{\mathbf{/g}}\)) & \(\mathbf{T_{m}}\) (\({}^{\circ}\)C) & \(\mathbf{\Delta H_{m}}\) (\(\mathbf{\mathbf{/g}}\)) & \(\mathbf{X_{r}}\) (\%) \\ \hline
**Neat PP** & 109.24 & \(-\)91.25 & 163.05 & 76.2 & 36.46 \\
**BC300/PP** & 119.83 & \(-\)76.64 & 163.60 & 62.75 & 37.53 \\
**BC400/PP** & 122.19 & \(-\)76.26 & 164.58 & 64.13 & 38.36 \\
**BC500/PP** & 124.06 & \(-\)83.76 & 165.35 & 71.47 & 42.75 \\
**BC600/PP** & 124.86 & \(-\)82.03 & 165.52 & 69.9 & 41.81 \\
**BC700/PP** & 124.65 & \(-\)80.97 & 165.60 & 68.23 & 40.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summarized results of DSC analysis of PP and its BC/PP composites. temperatures [39; 40]. Therefore, enhancements of these properties can be attributed to an increase in carbon content with higher pyrolysis temperature. The tensile strength of BC/PP composites was found to slightly decrease compared to neat PP. This is due to weak adhesion between the fillers and matrix. However, this property can be enhanced by using suitable compatibilizers, as evident in the literature [40]. Similarly, the elongation at break is a measure of materials ductility and expresses the capability of material to resist changes of shape under deformation without crack formation. The percentage elongation at break and percentage elongation at yield of neat PP and BC/PP composite systems are presented in Figure 10. It is observed that the addition of BC particles results in an abrupt decrease in both elongation at break and at yield as  
Figure 8: Stress-strain curves of BC/PP composites. Figure 9: Tensile strength and tensile modulus of BC/PP composites. compared to that of the neat PP.