Preparation of fluorine-free foam extinguishing agent based on silicone and hydrocarbon surfactants for markedly suppressing the pool fire

To solve the serious environmental hazard of fluorinated aqueous film-forming foam (AFFF), it is urgently to develop environmental-friendly fluorine-free foam extinguishing agents. In this study, a highly effective phosphate betaine silicone surfactant (PPSS) was prepared successfully, and then combined with various hydrocarbon surfactants to prepare the fluoride-free foam extinguishing agents. The effect of PPSS on the surface tension, foaming ability, foam stability and fire-extinguishing efficiency of fluoride-free foam extinguishing agents were investigated. The results show that the surface tension of PPSS is as slow as 20.68 mN/m, which imparts a lower surface tension to the mixed systems of PPSS and hydrocarbon surfactants. Especially, the mixture of PPSS and sodium alpha-olefin sulfonate (AOS) possess the lowest surface tension of 22.95 mN/m compared to the CTAB/PPSS and LAD-30/PPSS mixed systems. Moreover, AOS/PPSS mixture presents the excellent comprehensive performance with the critical micelle concentration (CMC) of 0.165 g/L, the surface tension at CMC value of 22.95 mN/m, the initial foam height of 111.9 mm, and the foam stability of 83.45%. Fire-extinguishing tests show that the foam obtained from AOS and PPSS exerts a wonderful fire-extinguishing efficiency compared to two commercial fire-fighting foams. In addition, the fire-extinguishing efficiency of foam extinguishing agents is closely related to the gas–liquid ratio. When the gas–liquid ratio is 17, the foam shows the maximum temperature reduction rate of 6.05 °C/s as well as the minimum extinguishing time of 38.9 s.