A green highly-effective surface flame-retardant strategy for rigid polyurethane foam: Transforming UV-cured coating into intumescent self-extinguishing layer

Nowadays, halogen-free high flame retardance of rigid polyurethane (RPU) foam without deteriorating its intrinsic performances is still a great challenge. Here, a green surface flame-retardant (SFR) strategy of RPU foam was proposed. In detail, a new halogen-free UV-curable self-extinguished coating was developed and then combined onto the surface of RPU, obtaining a surface flame-retardant RPU foam system (SFR-RPU). The SFR-RPU foams exhibit highly-efficient flame retardancy at a coating thickness of 25 µm, showing a fast self-extinguishing behavior. A compact porous char layer served as a good barrier can be rapidly formed on the surface of SFR-RPU. The detailed flame-retardant mechanism was proposed. Furthermore, when compared to neat RPU, the compressive strength of SFR-RPU foams is enhanced and the heat-insulation property is maintained perfectly. This facile, low-cost and environmental-friendly post-treatment of RPU foam could expand its fire safe commercial applications.