Flame-retardant mechanism of expandable polystyrene foam with a macromolecular nitrogen-phosphorus intumescent flame retardant

Expandable polystyrene (EPS) foam is largely used as the thermally insulating external wall in buildings and constructions, but it is extremely flammable because of the presence of almost 98% air into its porous structure, its high surface-area-to-mass ratio, and its elemental composition. Lots of serious fire disasters caused by EPS foam have posed great threats to people's properties and lives in recent years. Thus, a halogen-free, flame-retardant EPS is urgently needed, and its preparation is still a global challenge. To solve the problem that it is easy for EPS foam to form melt dripping and difficult for it to generate a char layer during the combustion process, a macromolecular nitrogen-phosphorus intumescent flame retardant (MNP) was selected to prepare flame-retardant EPS foam and good mechanical and flame-retardant properties were obtained. The scanning electron microscopy characterization revealed that MNP could penetrate into the gap between the beads, and a thin physical coating layer formed on the surface of the bead. The data from the thermogravimetry-Fourier transform infrared test indicated that a nitrogenous noncombustible gas was generated by the pyrolysis of MNP. When the MNP content increased to 30%, the limiting oxygen index and the smoking density rate of the EPS-MNP foam were 28.8 and 23.6, respectively, and a UL94V-0 classification was achieved. In addition, the heat-release rate, total heat-release, smoke produce rate, and carbon dioxide production of the EPS-MNP foams all decreased obviously; this was attributed to the flame-retardant effects of MNP in both the condensed and gas phases. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44356.