Research on Optimization of Flame Retardants for Performance Optimization and Foam Stability Enhancement in PFAS-Free Firefighting Foams

Current research on flame retardants in firefighting foams centers on fire suppression efficacy, with relatively limited mechanistic insights into how these agents regulate and optimize critical physicochemical properties such as foam stability. This study investigates the regulatory mechanisms of two flame retardants, ammonium pentaborate (APB) and magnesium hypophosphite (MHP), on the stability of PFAS-free (Per- and polyfluoroalkyl substances) foam, based on a blended system of silicone surfactants, hydrocarbon surfactants, and foam stabilizers. Experimental results reveal that the flame-retardant-regulated, PFAS-free foam system exhibits elevated viscosity and a prolonged drainage time. APB adversely affects the physicochemical properties of the foam, whereas MHP significantly enhances foam stability by strengthening the liquid film and delaying drainage. Further study revealed that within a certain concentration range, the addition of MHP consistently improves the stability of PFAS-free foam, with overall enhancement first increasing and then decreasing. The system achieved optimal stability at 0.2 wt% MHP, corresponding to the best fire suppression performance. This concentration-dependent effect provides an important theoretical basis for the optimal dosage of flame retardants in PFAS-free foams, addressing a critical research gap in the regulation and optimization of foam stability by flame retardants.