FIGURE 6 Digital photos of PU foam (a, b ) and MMT/PAAS-PU (c, d ) before and after burring. SEM images of MMT/PAAS-PU before (e, f ) and after (g, h ) burring.
Subsequently, the effect of MMT/PAAS coating on the flame retardancy of PU foam was studied by using a cone calorimetric test (CCT). The results are shown in Fig.7 and the characteristic parameters are shown in Table 2 . The most obvious should be shown to slow its ignition time. The time to ignition (TTI) of PU foam is 6s, while that of MMT/PAAS-PU is 10s. After the material was ignited, the heat release rate (HRR) of PU foam was almost higher than that of the MMT/PAAS-PU throughout the test (Fig. 7a ). Especially, its peak HRR (PHRR) was 381.42 kW/m3, 53.39% higher than that of MMT/PAAS-PU (177.80 kW/m3). Furthermore, the total heat release (THR) of PU foam is 40.69% larger (Fig.7b ). Unlike completely burned-out PU foam, MMT/PAAS-PU self-extinguished during the test (Fig. S7 in Supporting Information). Based on the above results, the MMT/PAAS coating will effectively improve the flame retardant properties and reduce damage even after ignition. Relatively, the peak mass loss rate (PMLR) is also higher than that of MMT/PAAS-PU, indicating that under a certain fire intensity, the degree of pyrolysis, volatilization, and combustion is more intense. Since the MMT/PAAS coating has an ordered layered structure and the structure remains after combustion, it plays a good role in the gas barriers. Therefore, compared with PU foam, its peak effective heat combustion (PEHC, reflecting the combustion degree of volatile gas in gas phase flame), total smoke production (TSP), peak CO yield (PCOY) and peak CO2 yield (PCO2Y) decreased by 15.76%, 53.03%, 47.58%, and 70.15%, respectively. The smoke produce rate (SPR) is always lower than PU foam (Fig.7c ) during the whole test. In a real fire, more than half of the deaths are caused by particulate matter and toxic gases (especially CO) generated by combustion.[47] MMT/PAAS coating in this study can effectively suppress smoke, which may greatly save people’s lives in real fires.
TABLE 2 The resulting parameters of CCT for PU foam and MMT/PAAS-PU