Halogen Free flame retardant rigid polyurethane foam with a novel phosphorus−nitrogen intumescent flame retardant

A novel phosphorous‐nitrogen containing intumescent flame retardant, toluidine spirocyclic pentaerythritol bisphosphonate (TSPB), was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR). Flame retardant rigid polyurethane foams (TSPB‐RPUF) were prepared by using TSPB. The flame retardancy of TSPB on rigid polyurethane foams (RPUF) was investigated by the limiting oxygen index (LOI), vertical burning test, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and FTIR. The results showed TSPB exhibited better compatibility with RPUF and lesser negative influence on the mechanical properties of TSPB‐RPUF. When the content of TSPB was 30 pph, the LOI of TSPB‐RPUF could reach 26.5%, and a UL‐94 V‐0 rating was achieved. Furthermore, the TSPB‐RPUF exhibited an outstanding water resistance that it could still obtain a V‐0 rating after water soaking. TGA showed the charring ability of RPUF was relatively poor, However, the residual weight of TSPB‐RPUF was improved greatly. SEM and FTIR indicated the intumescent chars formed from TSPB‐RPUF were compact and smooth, which was a critical factor for protecting the substrate material from burning.