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. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39581.
Ethanolamine spirocyclic pentaerythritol bisphosphonate (EMSPB), a novel intumescent flame retardant, was synthesized and used to improve the flame retardancy of rigid polyurethane foam (RPUF). The effects of EMSPB on the flammability, thermal stability, and mechanical properties of RPUF were discussed, respectively. Scanning electron microscopy (SEM) and compression strength tests showed that the EMSPB had favorable compatibility with the RPUF matrix and did not deteriorate the mechanical properties of the RPUF. Flammability of RPUF systems containing various contents of EMSPB was investigated by vertical burning test (UL-94) and limiting oxygen index (LOI) test. Results indicated that when the content of EMSPB was 25 wt%, the LOI of flame retardant RPUF could reach 27.5%, and a UL-94 V-0 rating was achieved. Thermogravimetric analysis showed that RPUF-containing EMSPB had a high yield of residual char at high temperatures, indicating that EMSPB was an effective charring agent. From the SEM observations of the residues of the flame retardant systems burned, the compact charred layers could be seen, which form protective shields to protect effectively the internal structure and inhibited the transmission of heat and heat diffusion during contacting fire.
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