## 3 Results
### Characterization of PS/OMMT Nanocomposite
#### 3.2.6 TGA and DTG Analysis  
Figure 10 presents TGA and DTG curves for the pure PS, PS/P-MMT, PS/P-SLS-MMT, and PS/P-KH570-MMT. It can be seen from the TGA curves that the weights of residue left of PS/OMMT nanocomposites at 550 \({}^{\circ}\)C were increased compared with the pure PS, which indicated the presence of  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **C (wt \%)** & **O (wt \%)** & **Al (wt \%)** & **Si (wt \%)** \\ \hline PS & 68.44 \(\pm\) 0.46 & 30.33 \(\pm\) 0.36 & 0.70 \(\pm\) 0.09 & 0.53 \(\pm\) 0.07 \\ PS/P-MMT & 63.62 \(\pm\) 0.24 & 31.45 \(\pm\) 0.40 & 3.52 \(\pm\) 0.17 & 1.41 \(\pm\) 0.12 \\ PS/P-SLS-MMT & 64.15 \(\pm\) 0.30 & 31.36 \(\pm\) 0.38 & 3.05 \(\pm\) 0.19 & 1.44 \(\pm\) 0.13 \\ PS/P-KH570-MMT & 67.92 \(\pm\) 0.33 & 28.61 \(\pm\) 0.29 & 2.33 \(\pm\) 0.11 & 1.14 \(\pm\) 0.12 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Distribution of the elements in PS, PS/P-MMT, PS/P-SLS-MMT, and PS/P-KH570-MMT samples found by EDS measurement related with SEM images given in Figure 9.  
Figure 9: SEM images of **(A)** PS, **(B)** PS/P-MMT, **(C)** PS/P-SLS-MMT, and **(D)** PS/P-KH570-MMT.  
the MMT in the polymer matrix. Furthermore, in contrast to the pure PS, the PS/OMMT nanocomposites exhibited significantly improved thermal stability, which could be attributed to the addition of OMMT in the polymer matrix [39]. The onset decomposition temperature corresponding to a mass loss of 10 wt % (\(T_{10\%}\)) of pure PS was 383 \({}^{\circ}\)C. As for the PS matrix filled with OMMT, the onset decomposition temperatures of PS/P-MMT, PS/P-SLS-MMT, and PS/P-KHS70-MMT were about 399 \({}^{\circ}\)C, 406 \({}^{\circ}\)C, and 416 \({}^{\circ}\)C, respectively, that was, 16 \({}^{\circ}\)C, 23 \({}^{\circ}\)C, and 33 \({}^{\circ}\)C higher than that of pure PS. The maximum mass loss temperature (\(T_{\text{max}}\), observed from DTG) was raised from 419 \({}^{\circ}\)C for the pure PS to 440 \({}^{\circ}\)C, 443 \({}^{\circ}\)C, and 449 \({}^{\circ}\)C for PS/P-MMT, PS/P-SLS-MMT, and PS/P-KH570-MMT, respectively. The enhancement in the thermal stability was due to the MMT layers forming a three-dimension network and a labyrinth pathway in the clay-polymer nanocomposite to prevent out-diffusion of the volatile decomposition products during thermal decomposition [40]. Meanwhile, the exfoliated structure of the MMT worked as a mass transport barrier, or a nucleating agent in the matrix, by limiting the heat transfer and absorbing the heat to decelerate the degradation of the polymers [41]. However, it was observed that the \(T_{10\%}\) and \(T_{\text{max}}\) of PS/P-SLS-MMT were higher than those of PS/P-MMT. The reason was perhaps that the maximum mass loss temperature of P-SLS-MMT was higher than that of P-MMT, as shown in Figure 4B, due to the electrostatic interaction between the anionic and cationic surfactants. This improvement in thermal stability was also observed in the PS/P-KH570-MMT nanocomposite. These results revealed that the double-modified MMT-containing PS nanocomposites showed higher thermal stability than that of the single-modified one. Interestingly, the \(T_{10\%}\) and \(T_{\text{max}}\) of the PS/P-KH570-MMT were higher than those of the PS/P-SLS-MMT. This result indicated that the double bonds of silanes grafting on the edges and surfaces of the MMT could react with styrene monomer increased chemical interaction between the MMT and the polymers, resulting in the improved interface interactions and enhanced the thermal stability [42]. In this case, the PS chains were covalently bonded on the surface of MMT, and the grafted KH570 molecules worked as the \"bridge\" connecting the PS chains and silicate layers, leading to an increase in the thermal stability.