Effect of Brominated Epoxy Resin Content on Thermophysical and Mechanical Properties of Intumescent Fire-Protective Coatings

Intumescent fire-protective coatings based on epoxy binders are widely used to enhance the fire resistance of steel structures due to their high adhesion, mechanical strength, and durability. However, epoxy binders undergo exothermic thermo-oxidative degradation, which can adversely affect fire-protective performance. In this study, the effect of brominated epoxy resin content on the fire-retardant behavior of intumescent coatings was investigated using two systems: one initially supporting flame propagation and one inherently self-extinguishing. For the initially combustible coating, partial substitution of the epoxy diane resin with a brominated analogue at 12.5% resulted in complete self-extinguishing behavior according to UL-94, while higher substitution levels (≥50%) caused a 20–28% reduction in fire-protective efficacy as assessed by BS 476. For the initially non-combustible coating, a decrease in fire-protective performance of 15–20% was observed regardless of the substitution degree. Thermal analysis showed that coatings containing brominated resins exhibit an onset of thermal degradation approximately 80 °C lower than halogen-free analogues. FTIR and SEM analyses revealed that brominated resins alter the thermolysis mechanism, promoting the formation of oxygen-containing degradation products and a more heterogeneous, irregularly porous foamed char, thereby reducing its thermal insulation capacity. Overall, brominated epoxy resins exert a dual effect, improving self-extinguishing behavior while impairing fire-protective efficacy under prolonged thermal exposure. Brominated resin contents in the range of 10–50% represent a practical compromise, enabling self-extinguishing behavior while maintaining acceptable fire-protective performance.