Thermoresponsive Hybrid Colloidal Capsules as an Inorganic Additive for Fire-Resistant Silicone-Based Coatings

Improving the fire-resistant efficiency of silicone-based polymeric coatings is important in the building industry and electrical utilities. In this study, the water-containing hybrid calcium carbonate (CaCO3)–silica (SiO2) colloidal capsule has been developed and optimized as an inorganic flame-retardant additive. This capsule exhibits excellent thermal stability up to 1000 °C with a remaining intact hollow spherical structure. When used as an inorganic filler at 15 wt %, it not only reduces the potential fire hazards by over 44% (i.e., the sumHRC reduced from 112.00 J/g K to 62.00 J/g K) but also improves the heat-barrier efficiency by over 30% (i.e., the temperature at the steady state reduced from 350 to 360 °C to below 250 °C) of the silicone-based polymeric coatings. In addition, the capsule–polymer composite coating exhibits excellent ductility which can withstand heat-induced mechanical stresses and prevent crack propagation under radiative heating conditions. The fire-resistant mechanism of the colloidal capsule is related strongly to the encapsulated water core and the reactions between SiO2 and CaCO3 at elevated temperatures. They not only contribute to a cooling effect on the flammable pyrolysis gases but also induce the insulative effect to the resulted char during combustion. The significant advances in this study will have a high impact in customizing the functional inorganic additives for a better design of the flame-retardant composite coating.