Synthesis, Characterization Of A Bicyclic Phosphonate And Its Flame Retardancy To RPUF

Rigid polyurethane foam（RPUF）is widely used in construction,transportation,aviation and other fields because of its good thermal insulation and mechanical properties.However,its application has great limitations because of its flammability and the large amount of smoke generated during combustion.Study on flame retardant RPUF is an effective way to solve the above problems.Liquid flame retardant bis（（5-ethyl-2-methyl-2-oxido-1,3,2-dioxaphosphinan-5-yl）methyl）methylphosphonate（BDMP）was synthesized from trimethylol propane and dimethyl methylphosphonate.Its structure was characterized by Fourier transform infrared spectroscopy,¹H-NMR and ³¹P-NMR.The reaction process was tracked by gas chromatography,and the catalytic effects of ionic liquids[Bmim]BF₄ andγ-Al₂O₃ on the synthesis of BDMP were compared.It was found that[Bmim]BF₄ had a better catalytic effect.The flame retardant RPUF was successfully prepared using BDMP.At the addition amount of 20 wt%,the compressive strength of RPUF decreased somewhat,but the ultimate oxygen index increased from 18.8%to 25.9%,and the UL-94 rating was V-0,which could achieve self-extinguishing off fire.The peak heat release rate at this time was 153.5 k W/m² and the total heat release was 27.5 MJ/m²,which decreased by 36.07%and 35.85%,respectively,compared with no flame retardant added,due to the fact that BDMP could effectively promote carbon formation.BDMP was found to be compatible with RPUF by scanning electron microscopy,and it is an ideal flame retardant for RPUF.The results of thermogravimetric tests showed that BDMP decomposes at a relatively low temperature at the beginning of combustion to exert flame retardant effects and can slow down the thermal decomposition rate of flame retardant RPUF.The activation energy of thermal decomposition of RPUF and flame retardant RPUF was calculated using the Kissinger and Flynn-Wall-Ozawa methods of thermal decomposition kinetics analysis.The calculation results of Kissinger method show that adding BDMP can increase the activation energy required for thermal decomposition of RPUF as a whole and improve the flame retardancy.The thermal decomposition mechanism of RPUF and flame retardant RPUF was analyzed based on the calculation results of Flynn-Wall-Ozawa method.The results of the thermogravimetric infrared coupling test showed that the introduction of BDMP could inhibit the complete combustion of RPUF,reduce the overall gas release,generate more incompletely burned organic gases,and exhibit gas-phase flame retardant mechanism.