Synthesis of Diphenylphosphine Oxide Derivative and Its Flame Retardant Application in Epoxy Resin
A type of reactive phosphorus based flame retardant, hydroxy(4-hydroxyphenyl)methyl)diphenylphosphine oxide (DPO-H), was synthesized and characterized by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopies. 4,4′-Diaminodiphenylsulfone (DDS) was used as the curing agent and DPO-H was used as the reactive flame retardant and co-curing to prepare the flame-retardant epoxy resins with different P contents. It can be observed that the introduction of DPO-H could enhance the transparency of epoxy resin. Flame-retardant epoxy resin samples were investigated by limit oxygen index (LOI) test, vertical burning (UL-94) testing, cone calorimetry test and thermogravimetric analysis (TGA). The results indicated that DPO-H can increase the flame retardation and carbon formation of epoxy resin. The flame-retardant epoxy resin sample with P content of 0.5 wt% can reach UL-94 V-0 rate, and LOI value increased to 29.6%. The flame-retardant mechanism of the DPO-H modified flame-retardant epoxy resin was analyzed by thermogravimetry-infrared combination (TG-IR), pyrolysis gas chromatography mass spectrum (PY/GC-MS) and scanning electron microscope (SEM). The results showed that the introduction of DPO-H can inhibit the pyrolysis of epoxy resin effectively. Epoxy resin modified by DPO-H had evident flame-retardant effect both in gas phase and condensation phase.
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