Highly effective flame-retardant coatings consisting of urea-formaldehyde resin/aluminium hydroxide/boric acid for polystyrene foam: Properties and mechanisms investigation

The flame-retardant properties of expanded polystyrene (EPS) foam were enhanced by constructing a flame-retardant coating on its surface using melamine modified urea-formaldehyde resin (MUF), H₃BO₃, and Al(OH)₃ as raw materials. A coating consisting of an equal proportion of H₃BO₃ and Al(OH)₃ demonstrated superior mechanical properties, flame-retardant properties, and smoke suppression ability. Additionally, this coating increased the compressive strength of EPS material by 43.30 %, raised the carbon residue from 0.14 % to 32.4 %, elevated the limiting oxygen index to 37.4 %, and achieved a vertical combustion rating of V-0 according to UL-94 standards. These improvements were accompanied by a reduction in peak heat release rate by 59.36 %, total smoke production by 51.99 %, maximum smoke density by 80.13 %, and smoke density rating by 89.52 %. Furthermore, the coated material exhibited satisfactory water resistance, thermal insulation, and transparency. Simulation results show that the MUF/H₃BO₃/Al(OH)₃ coating system generated various metal and non-metal compounds during combustion along with NO_x, CO_x, and H₂O gases. The beneficial flame-retardant effect of the coating can be attributed to the hybrid flame-retardant effect of H₃BO₃ and Al(OH)₃ in both the gas and condensed phases.