Reinforcing Condensed Phase Flame Retardancy through Surface Migration of Brucite@Zinc Borate-Incorporated Systems

An efficient brucite@zinc borate (3ZnO·3B₂O₃·3.5H₂O) composite flame retardant (CFR), consisting of an incorporated nanostructure, is designed and synthesized via a simple and facile electrostatic adsorption route. It has been demonstrated that this incorporated system can enhance the interfacial interaction and improve the mechanical properties when used in ethylene-vinyl acetate (EVA) composites. Meanwhile, in the process of burning, the CFR particles can successively migrate and accumulate to the surface of the burning zone, increasing the local concentration and rapidly generating a compact barrier layer through a condensed phase reinforcement mechanism even at a lower loading value. Especially, compared with the EVA/physical mixture (PM, with the same proportion of brucite and zinc borate), the heat release rate (HRR), the peak of the heat release rate (PHRR), the total heat released (THR), the smoke production rate (SPR), and mass loss are considerably reduced. According to this study, controlling the nanostructure of flame-retardant particles, to improve the condensed phase char layer, gives a new approach for the design of green flame retardants.