Effect of titania, barite, and kaolinite fillers on char layer formation in water-based intumescent fire-retardant coatings

Intumescent fire-retardant coatings are widely applied as they combine designable aesthetics and fire protection without compromising substrate properties. When exposed to heat, intumescent fire-retardant coatings expand and build an insulating char. This study presents an investigation of the char by addition of kaolinite, barite, and titania as functional fillers in intumescent coatings. Expansion experiments at 400°C with custom build image analysis showed that kaolinite inhibited (0.03 mm/s, expansion factor ≈ 7), whereas barite acted synergistically on the expansion ability (0.59 mm/s, expansion factor ≈ 85). The resulting char density and the visual inspection showed that barite char was less compact, with cracks and voids. Evaluation of fire performance by single burning item tests resulted in Euroclass C for the barite system and Euroclass A2/B for the titania system. Post-heating chars demonstrated poor thermostability of barite char, and subsequent FTIR spectroscopy revealed that titania char formed the thermostable titanium pyrophosphate. Further inspection of the titania char revealed a uniform closed cell structure with mean bubble sizes of 26–56 µm. Titania coating expands rapidly (0.37 mm/s, expansion factor ≈ 60) and forms a structurally stable tumescent char with a compact and uniform porous structure exhibiting resistance to char oxidation at sustained heating.