A review of flame retardants for rigid and flexible polyurethane (PU) foams shows that progress is centred on PIN solutions. The authors underline the high fire risks of PU foams, the consequent need for flame retardants to inhibit ignition and reduce flammability, and the “the serious health hazards and environmental concerns of halogen compounds”. 270 references are reviewed showing the extent of research into PIN FR solutions. Chemical decomposition and fire reaction of PU are discussed. FR solutions presented in detail include phosphorus-based PIN FRs, phosphorus-nitrogen PIN FRs, carbon-based (e.g. expandable graphite EG, EG + hypophosphite), inorganic PIN FRs (including synergists such as boron compounds), organically modified nanoclays, siloxanes. Reactive PIN FRs solutions (such as modified urea formaldehyde or reactive phosphorus polyols) can have lower impacts on foam processing and mechanical performance. Post-processing foam PIN FR application (Layer-By-Layer LBL, sol-gel, freeze drying) are outlined. The conclusions underline the need to move away from halogenated FRs and the interest of synergistic PIN FR combinations.
“Recent Advancements in Flame-Retardant Polyurethane Foams: A Review”, A. Yadav et al., Ind. Eng. Chem. Res. 2022, 61, 15046−15065 https://doi.org/10.1021/acs.iecr.2c02670