Experimental study on fire extinguishing performance of fluorine-free foam with nanoparticle-enhanced stability

Nanosilica (SiO₂) particles can effectively improve the stability and burn back performance of foam fire extinguishing agents, and thus are widely used. However, due to the poor dispersibility of SiO₂ in water, it tends to aggregate easily, which restricts the exertion of its performance. This study introduces nanocellulose (CNF) as a synergistic stabilizer to enhances the thermal stability and fire extinguishing efficiency of foam by improving the dispersibility of SiO₂ and the mechanical strength of the foam. The results of our study indicated that the coarsening rate of the 1227/SiO₂/CNF foam system was reduced by nearly 10⁵ μm³/s with the addition of 0.03 wt% CNF. Moreover, the CNF-stabilized foam not only exhibited a longer half-life at 80 °C compared to the 1227/SiO₂ foam system at 40 °C, but also demonstrated a substantially improved suppression of n-heptane vapor due to the presence of CNF. During the invasion of the oil phase into the liquid film, CNF enhanced the stability of the foam system by improving the dispersion uniformity of SiO₂ within the liquid film and increasing mechanical strength of the liquid film. The 1227/SiO₂/CNF foam system could completely extinguish the flame within 30 s in the small-scale fire extinguishing test, which demonstrated the same extinguishing efficiency with aqueous film-forming foam extinguishing agent (AFFF). Additionally, the CNF-stabilized foam could maintain the stability in burn back test for about 1800 s, which was significantly better than that of AFFF, demonstrating that CNF plays an important role in enhancing the foam's burn-back resistance.