Synergistic Effect Between Oxides and Flame Retardants to Construct Multilayer Char in Intumescent Coatings for Steel Structure

Intumescent coating (IC) for structural steel is mandatory to ensure people and building safety. This study investigated the synergistic effect of oxide fillers and flame retardant [Melamine polyphosphate (MPP) and pyrophosphate (PAPP)] to optimize the char structure in fire for the improvement of thermal insulation of the coating. Results indicated that active oxides (TiO₂ and ZnO) would reduce decomposition temperature, thereby facilitating earlier swelling of the char layer to prevent the initial heat transfer. The inert fillers (SiO₂ and Al₂O₃) or pyrolysis product of SAE/MPP/PAPP/TiO₂ mixture would improve the mechanical strength of the char barrier. Oxide fillers would lower down the initial decomposition temperature to around 300°C, and increase the solid residue. Addition of TiO₂ got the lowest stabilized steel-backside temperature at 150°C after 2-h burning compared with addition of other oxides. Both heat and toxic smoke release decreased in cone test. The morphology and FTIR spectra of char layers suggested that TiO₂-IC can form a mechanically strong, porous, and homogeneous swelling layer in the middle, with a ‘heat shield’ built by titanium pyrophosphate and residue TiO₂ outside, and a continuous adhesion layer of retained organic material inside, thereby decreasing the thermal conduction, blocking the heat convection and reducing the thermal radiation. The excellent synergistic thermal isolation of TiO₂ and MPP/PAPP system puts forward a novel way for further development of intumescent coatings for steel structure.