## 3 Results and Discussion
### Combustion Behaviors of EVA Composites  
The combustion behavior of EVA/MH/PCS/DVB is illustrated in Figure 11, and the combustion parameters are presented in Table 5. The HRR curve of EVA/MH/PCS was different from EVA/MH. The HRR of EVA/MH/PCS was effectively suppressed, especially before 250 s compared with EVA/MH (Figure 11a), and the THR\({}_{\text{6 min}}\) of EVA/MH/PCS (84 MJ/m\({}^{2}\)) was higher than that of EVA/MH (90 MJ/m\({}^{2}\)) by 6 percentage points (Figure 11b and Table 5), while the TSP of EVA/MH/PCS (7.3 m\({}^{2}\)) was increased by 40%, which was closely related to the formation of the condensed residue. The tarry and bubbly surface of the residue formed during the combustion of EVA/MH. The bubble cracked back and forth, and thus no intumesent phenomenon was found for the low-strength surface char of the residue (Figure 11e). For EVA/MH/PCS, the migration of PCS to the surface during the combustion helped enhance the strength of the surface char [11], leading to a condensed and cohesive surface char as well as obvious intumesent behavior, which were effective in reducing the HRR, but the migration of PCS also releases more small molecular degradation products to the gas phase, which can increase the TSP. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **EVA/MH** & **EVA/MH/PCS** & **EVA/MH/PCS/DVB** & **EVA/MH/PCS+DVB** \\  & **50/50** & **50/47/3** & **50/47/2/1** & **50/47/2+1** \\ \hline TTI (s) & 74 & 71 & 68 & 60 \\ tpHRR\({}_{1}\) (s) & 280 & 201 & 219 & 195 \\ pHRR\({}_{1}\) (kW/m\({}^{2}\)) & 438.8 & 291.1 & 396.7 & 450.6 \\ tpHRR\({}_{2}\) (s) & - & 296 & - & - \\ pHRR\({}_{2}\) (kW/m\({}^{2}\)) & - & 426.6 & - & - \\ THR\({}_{\text{6 min}}\) (MJ/m\({}^{2}\)) & 90 & 84 & 90 & 89 \\ TSP\({}_{\text{6 min}}\) (m\({}^{2}\)) & 5.2 & 7.3 & 5.4 & 6.9 \\ Residue\({}_{\text{6 min}}\) (\%) & 36.9 & 38.7 & 40.5 & 39.5 \\ FPI (s-m\({}^{2}\)/kW) & 0.17 & 0.17 & 0.17 & 0.13 \\ FGI (kW/m\({}^{2}\)-s) & 1.24 & 1.16 & 1.38 & 1.77 \\ THR\({}_{\text{6 min}}\) & 1.94 & 1.89 & 1.93 & 1.92 \\ TSPI\({}_{\text{6 min}}\) (m\({}^{2}\)) & 0.68 & 0.88 & 0.67 & 0.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The combustion parameters of EVA composites. Figure 10: Snap images of the combustion state and the residue after the LOI test. For the EVA/MH/PCS/DVB composite, the HRR was similar to EVA/MH, which means MH/PCS/DVB had little effect in improving the heat release behavior of the EVA composites compared with MH/PCS, but it was more effective than MH/PCS+DVB (Figure 11a). It is worth noting that the TSP was decreased by 26% compared with EVA/MH/PCS and 21% compared with EVA/MH/PCS+DVB (Figure 11c). In addition, the residue was higher than EVA/MH/PCS by 1.8 percentage points and higher than EVA/MH/PCS+DVB by 1 percentage point (Figure 11d). Such differences among EVA/MH/PCS, EVA/MH/PCS/DVB, and EVA/MH/PCS+DVB are related to the PCS  
Figure 11: The combustion behaviors of EVA composites: (**a**) HRR, (**b**) THR, (**c**) TSP, (**d**) mass, and (**e**) digital photos of residual char after the CONE test. contents and states in the composites and the char residue formation. PCS migrates significantly during combustion. For the EVA/MH/PCS/DVB composite, the continuity of the surface char was inferior to EVA/MH/PCS but obviously superior to EVA/MH/PCS+DVB (Figure 11e), indicating that the 2 wt.% PCS in the composite was not enough to form a continuous surface char, but the continuity could be improved when the PCS was cross-linked by DVB, which led to the apparent differences in HRR and TSP. According to the combustion parameters of the composites, the fire performance index (FPI), fire hazard growth index (FGI), heat release index (THRI), and smoke emission index (TSPI) were calculated to further evaluate the fire safety of the composites [38]. The fire safety index values of the composites are shown in Table 5. Compared with EVA/MH, the FGI of EVA/MH/PCS decreased by 7.6% and the TSPI increased by 29%. The FGI of EVA/MH/PCS/DVB increased by 11%, while the TSPI had little change.