Synergistic effect of industrial- and bio-fillers waterborne intumescent hybrid coatings on flame retardancy, physical and mechanical properties

Demands on effective intumescence have led to the development of waterborne intumescent coatings. In this study, potential flame retardant additives were hybridized with different compositions of titanium dioxide and aluminum hydroxide as industrial fillers, and rice husk ash and chicken eggshell as bio-fillers. Aiming to improve the flame retardancy, six coating formulations were characterized based on Bunsen burner fire protection, surface spread of flame, fire propagation and oxygen index. The synergistic effect of fillers on intumescent coating was investigated in detail through physical and mechanical properties based on water resistance, scanning electron microscopy (SEM), eco-label, adhesion and char strength. Significant improvement indicates all coatings require high oxygen concentration to support the burning. From BS 476: Part 7, all coatings were classified as Class 1 showing least distance of flame spreading and fulfilled the best Class O, which limits the amount of heat released in BS 476: Part 6. Coating hybrid with RHA demonstrated the lowest equilibrium temperature of 181 °C, while coating with all hybrid industrial- and bio-fillers had excellent char strength with 43% decremented from its initial thickness. Usage of industrial- and bio-fillers’ hybrid coatings is a realistic and promising way to meet the fire protection features to control the fire growth and limit the fire spread due to their flame retarding efficiency. This study presents a promising approach of hybrid fillers with excellent smoke suppression, enhancement of mechanical strength and high insulation char to slow down the burning behaviors, along with the improvement of anti-dripping tendency.