Enhanced flame-retardant and thermal insulation properties of epoxy coatings via surface-modified hollow glass microsphere

Applying fireproof coatings to building structures can effectively reduce temperature increases and delay structural damage during a fire, thereby extending evacuation time and improving building safety. However, flame-retardant functionality alone is no longer sufficient. This study employed a P/Si composite halogen-free flame retardant, KHDOPO, to surface-modify hollow glass microsphere(HGM) to enhance its dispersibility, compatibility, and flame-retardant properties in the coating. The modified HGM (KHGM) was integrated into an epoxy resin (EP) coating using covalent modification and in-situ dispersion techniques. This approach produced a coating with outstanding thermal insulation and flame-retardant characteristics. Results demonstrated that the KHGM/KHDOPO/EP coating exhibited optimal thermal insulation and maintained excellent flame retardancy, achieving a UL-94 V-0 rating. In testing, its back temperature reached 354 °C, which is 55% of that of the EP coating and 90 °C lower than that of the unmodified HGM. The thermal conductivity at room temperature was 44% lower than that of EP. Observed in the gaseous and condensed phases, the synergistic effects have improved flame retardancy efficiency and reinforced the protective char layer, evidenced by a low Raman I D /I G value of 2.61. During the cone calorimetry test, the PHRR value registered at 517.75 kW/m 2 , marking a 58.9% reduction compared to the unmodified coating. In summary, the coating containing 5% surface-modified HGM demonstrates significant potential in the field of safety protection.