A phosphorous-nitrogen intumescent flame-retardant, 2,2-diethyl-1,3-propanediol phosphoryl melamine (DPPM), was synthesized and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Flame-retardant rigid polyurethane foams (RPUFs) with DPPM (DPPM-RPUF) as fire-retardant additive were prepared. Scanning electron microscope (SEM) and mechanical performance testing showed that DPPM exhibited a favorable compatibility with RPUF and negligibly negative influence on the mechanical properties of RPUF. The flame retardancy of DPPM on RPUF was investigated by the limiting oxygen index (LOI), vertical burning test and cone calorimeter. The LOI of DPPM-RPUF could reach 29.5%, and a UL-94 V-0 rating was achieved, when the content of DPPM was 25 php. Furthermore, the DPPM-RPUF exhibited an outstanding water resistance that it could still obtain a V-0 rating after water soaking. Thermogravimetric analysis showed that the residual weight of RPUF was relatively low, while the charring ability of DPPM-RPUF was improved greatly. Real-time Fourier transform infrared spectroscopy was employed to study the thermo-oxidative degradation reactions of DPPM-RPUF. The results revealed that the flame-retardancy mechanism of DPPM in RPUF was based on the surface charred layer acting as a physical barrier, which slowed down the decomposition of RPUF and prevented the heat and mass transfer between the gas and the condensed phases. storage and electromagnetic interference shielding fields due to its high mechanical properties, insulated properties, etc. 1-4 However, one of its major defects is its flammability, which limits its further applications. 5,6 The improvement of the flame retardancy of RPUF has currently been an important subject among the developments of new polymer foam materials. 7,8 Traditionally, the main flame retardants for RPUF are the halogen-based compounds such as pentabromodiphenyl ether, chloroethylphosphate, etc, which may endow RPUF excellent flame retardation. 9 However, when burning, such retardants release a lot of toxic gases which pollute environment and damage people's health. 10-14 Thus, the environmentally-friendly flame-retardant additives with good flame retardancy are particularly needed. In recent years, the phosphorus-nitrogen intumescent flame retardants (IFR) have been widely used as halogen-free additives because they provide excellent fire protection with less smoke and lower toxicity. 15,16 Traditional IFRs are mixtures, which usually consist of an acid source (eg, ammonium polyphosphate), a carbonizing agent (eg, pentaerythritol, sorbitol) and a foaming agent (eg, melamine). The IFRs system usually experiences an intense expansion and forms protective charred layers that serve as a physical barrier to protect the underlying material from flux or flame. 14,15 In spite of many advantages, IFRs have 2 issues, ie, low water solubility and high thermal stability. 17 In addition, they are poorly compatible with the RPUF matrix, which weakens the mechanical properties of ...
