Synthesis of a novel liquid phosphorus-containing flame retardant for flexible polyurethane foam: Combustion behaviors and thermal properties

Abstract

To overcome the shortcomings of limited flame retardant efficiency and migration of commercialized dimethyl methylphosphonate (DMMP) in flexible polyurethane foams (FPUFs), a novel liquid phosphorus-containing flame retardant named bis((dimethoxyphosphoryl)methyl) phenyl phosphate (BDMPP) was synthesized via dimethyl (hydroxymethyl)phosphonate and phenyl dichlorophosphate and applied into FPUFs. Compared with DMMP, BDMPP contains two kinds of phosphorus with higher molecular weight and one kind of its phosphorus is very similar with that of DMMP. The flame retardancy of FPUFs was evaluated by limiting oxygen index (LOI), vertical burning test and cone calorimetry test. In contrast with DMMP, BDMPP showed better flame retardancy. When 20 wt% BDMPP (relative to polyether polyol) was incorporated, the foam composite obtained an LOI value of 23.0% and passed the vertical burning test. Thermogravimetric analysis (TGA) demonstrated that BDMPP containing FPUFs had better thermal stability and more char yield than those of DMMP containing FPUFs. Moreover, accelerated heat ageing test revealed that BDMPP exhibited better resistance to migration than DMMP. The flame retardant mechanisms were investigated by FTIR, thermogravimetric analysis/infrared spectrometry (TG-IR), scanning electron microscopy and Raman spectroscopy. Compared with DMMP, the increase in the flame retardancy of BDMMP in FPUFs is possibly due to its different structure.