## 3 Results and Discussion
### Thermal Stability  
The thermal stability of the different composites was evaluated by TGA measurements. The TGA result of E-POSS-reinforced E51 is illustrated in Figure 7A, and the data are summarized in Table 2. It can be seen that the T\({}_{\text{d5\%}}\) of E51 + E-POSS (10 wt%) was higher than that of the E51 sample, which indicates that the thermal stability of the E51 + E-POSS sample was improved by adding E-POSS into the epoxy resin, as the bond energy of the Si-O bond is high, and the high temperature stability of POSS is good. The dissociation energy of the Si-O bond (460 kJ/mol) was higher than that of the Si-C bond (318 kJ/mol), or the C-C bond (344 kJ/mol) or C-O bond (345 kJ/mol) [33; 34]. A higher bond energy will lead to a higher thermal decomposition temperature. As the cube structure of E-POSS is mainly composed of Si-O bonds, the incorporation of E-POSS into E51 resin will increase the number of Si-O bonds in the composite. Only under higher temperature (higher energy) will an E51 + E-POSS (10%) sample be destroyed. It is worth noting that the residue of the E51 + E-POSS (10%) sample was higher than that of the E51 sample (Table 2). The results show that the incorporation of E-POSS into the E51 resin could reduce the rate of sample mass loss, leading to a higher residue at the same temperature. The TGA result of E-POSS reinforced with E51 is illustrated in Figure 7A. It can be seen that the T\({}_{\text{d5\%}}\) value of E51 + E-POSS (E-POSS (10%)) was higher than that of the E51 sample, indicating that the incorporation of E-POSS into the epoxy resin could increase the thermostability of the obtained E51 + E-POSS hybrid because the E-POSS structure is mainly composed of Si-O bonds.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample ID** & **T\({}_{\text{d5\%}}\) (\({}^{\circ}\)C)** & **Residues (wt%)** \\ \hline E51 & 336 & 2.4 \\ E51 + E-POSS (10\%) & 354 & 11.5 \\ E51 + GF (16\%) & 366 & 15.3 \\ E51 + E-POSS (10\%) + GF (16\%) & 378 & 21.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The thermal degradation data of TGA.  
The TGA curves of the E51 + GF composite are presented in Figure 7B and the data are summarized in Table 2, which show that the initial decomposition temperature and residue were improved. The T\({}_{\text{d}\%}\) of the E51 + GF (16%) sample was higher than that of the E51 sample, and the residue of E51 + GF (16%) was also higher than that of the E51 sample. The incorporation of GF into E51 could improve the thermal decomposition temperature and reduce the rate of mass loss, resulting in a larger weight of residue under the same high-temperature conditions. The GF contributes to the increased thermostability and reduced mass loss rate, owing to its inorganic properties, because the softening point of common glass fiber is generally higher than 600 \({}^{\circ}\)C. The TGA curves of the ternary composite E51 + E-POSS (10%) + GF (16%) sample are shown in Figure 7C and the results are summarized in Table 2. The T\({}_{\text{d}\%}\) and residue of the E51 + E-POSS (10%) + GF (16%) sample were 378 \({}^{\circ}\)C and 21.2%, and increased remarkably by 42 \({}^{\circ}\)C and 18.8% compared with the E51 sample. In addition, the thermal stability of the ternary composite E51 + E-POSS (10%) + GF (16%) sample was better than that of the E51 + E-POSS (10%) and E51 + GF (16%) sample. Because the ternary composite of the E51 + E-POSS (10%) + GF (16%) sample contains a large number of stable Si-O bonds, inorganic GF can slow down the thermal decomposition temperature and increase the quality of residues. These results show that the synergistic effect between E-POS and GF was beneficial to improve the heat resistance of the epoxy resin. In other words, the thermal stability of E-POSS and GF improves the heat resistance of E51 composite [35; 36].