Surface-coating engineering for flame retardant flexible polyurethane foams: A critical review

Flexible polyurethane foams (FPUFs) have been extensively used in furniture, carpet, automobiles, etc., due to their superior thermal insulation, low bulk density and superior chemical resistant properties. Unfortunately, they are extremely ignitable and flammable, and release a large amount of combustion heat accompanied by plenty of smoke and toxic gases upon ignited, thus posing a potential threat to lives and property. The minimization of their fire hazards is usually realized by the addition of flame retardants, and the creation of flame retardant coating. As compared with the former approach, the surface coating strategy has gained much more interests because it improves the flame retardancy of FPUFs without compromising mechanical properties. To date, several surface-coating approaches, including in situ deposition, sol-gel process, plasma technique and layer-by-layer (LBL) assembly have been developed for improving the fire safety performance of FPUFs. This review focuses on the recent advances in flame retarded FPUFs by employing the surface coating approaches. This work also summarizes the design of intumescent and non-intumesecent fire retardant coatings applied to the fire protection of FPUFs by depositing (nano)coatings on their surfaces. Special attention will be paid to the FPUFs treated with flame retardant nanocoating via the LBL assembly. Moreover, this work further compares the advantages and disadvantages of these surface coating methods, and finally presents some future research opportunities on flame retardant FPUFs materials.