Water-based flame retardant coating using nano-boehmite for expanded polystyrene (EPS) foam

• New coating based on PVOH and boehmite was developed as an alternative to HBCD.
• Coating level and thickness depend on several parameters as viscosity, dips number and impregnation time.
• Fire behaviour was assessed using a widely used industrial test.
• Relations between coating properties and fire rating were established.

Expanded polystyrene (EPS) foam has been successfully flame retarded by a water-based coating containing nanoparticles of boehmite and poly(vinyl alcohol) (PVOH) as char former. Boehmite enhances the charring of PVOH. The influence of suspension viscosity, coatings number, impregnation time and drying method was studied to monitor the amount of coating deposited and the coating thickness. The coating suspension is able to penetrate into the core of the foam. EPS without hexabromocyclododecane (HBCD) is upgraded from F to E rating according to the NF EN ISO 11925-2 standard when the penetration of coating suspension into the core is high enough, due to the formation of a char layer reinforced by nano-boehmites even if EPS does not shrink away from the flame.