## 3 Results and Discussion
### Composites Characterization
#### 3.2.3 Thermogravimetric Analysis (TGA)  
The thermal stability of polymeric materials is an important parameter, since the thermal stability of polymer materials can be a limiting factor in both processing and end-use applications [32]. Thermal degradation of the PP and BC/PP composites was determined from the weight loss during heating. The weight loss (TGA) and the derivative weight loss (DTG) curves are shown in Figure 6a,b, respectively. The values of temperatures for 5% and 15% weight loss (T\({}_{5\%}\) and T\({}_{15\%}\)), and also the maximum decomposition temperature (T\({}_{\rm max}\)) are summarized in Table 4. It can be observed from Figure 6a that the thermal degradation of the neat PP and its BC/PP composites takes place in a single step. The maximum temperature of decomposition (T\({}_{\rm max}\)) for the neat PP was found to be around 477 \({}^{\circ}\)C, while the temperatures for 5% and 15% weight losses were observed at 395 \({}^{\circ}\)C and 433 \({}^{\circ}\)C, respectively.  
Figure 5: FTIR of BC/PP composites.  
Figure 6a also indicates that all BC/PP composite samples show a delayed onset degradation temperature compared to the neat PP. This delayed in degradation process is an indication of improved thermal stability of the composites, which is due to the addition of the thermally stable biochar.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**TGA**} & \multicolumn{2}{c}{**DTG**} \\ \cline{2-5}  & \(\mathbf{T_{Soft}}\), \(\mathbf{{}^{a}}\) (\(\mathbf{{}^{c}}\)C) & \(\mathbf{T_{15 wt}}\), \(\mathbf{{}^{b}}\) (\(\mathbf{{}^{c}}\)C) & **Residual wt \%** & \(\mathbf{T_{max}}\) (\(\mathbf{{}^{c}}\)C) \\ \hline
**Neat PP** & 395 & 433 & 0 & 477 \\
**BC300/PP** & 416 & 456 & 14.80 & 485 \\
**BC400/PP** & 457 & 473 & 15.47 & 489 \\
**BC500/PP** & 465 & 478 & 18.69 & 490 \\
**BC600/PP** & 467 & 478 & 17.02 & 491 \\
**BC700/PP** & 466 & 478 & 20.03 & 490 \\ \hline \hline \end{tabular}  
* \(\mathbf{T_{Soft}}\) represents the temperature at which 5 wt \% weight loss rate occurred, \(\mathbf{{}^{b}}\) T\({}_{15 wt}\), represents the temperature at which 10 wt \% weight loss rate occurred, and \(\mathbf{{}^{c}}\) T\({}_{\max}\) represents the temperature at which the maximum weight loss rate occurred.  
\end{table}
Table 4: Summarized results of TGA analysis of PP and BC/PP composites.  
Figure 6: TGA (**a**) and derivative weight loss (DTG) (**b**) curves of BC/PP composites.  
This improvement in the resistance to thermal degradation can be attributed to the hindered diffusion of volatile decomposition products within the BC/PP composites. It also due to the barrier effect of the addition of BC to the PP matrix, causing mass transfer limitations of volatile gases produced during thermal transformation. The biochar is considered to be an amorphous material that is structurally disordered in nature. However, some rearrangement of molecular layers takes place between chains of carbon or/and carbon molecules depending on the temperature of pyrolysis and residence time [33]. Such type of carbon network transformation into the turbostatic stack-like structure of the biochar has already been reported [33; 34]. It is concluded, therefore, that this biochar can act as a barrier element in the composites. Amongst the composites samples, it can be observed that the BC700/PP sample shows higher thermal stability than the others.