Preparation of DOPO‐derived magnesium phosphate whisker and its synergistic effect with ammonium polyphosphate on the flame retardancy and mechanical property of epoxy resin

In this study, a magnesium phosphate whisker (DPM‐H) was synthesized by the acid–base neutralization reaction between magnesium hydroxide and 10‐hydroxy‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO‐OH) at 120°C. A new synergistic intumescent flame retardant (IFR) for epoxy resin (EP), which was composed of DPM‐H and ammonium polyphosphate (APP) was thoroughly studied. When the IFR loading was 8%, with the DPM‐H to APP weight ratio at 1:7, the prepared flame‐retardant EP (EPDA‐2) passed the vertical burning tests (UL‐94) V‐0 rating and obtained the limiting oxygen index (LOI) value of 29.3%. Microscale combustion calorimetry (MCC) results showed that the total heat release (THR) of EPDA‐2 reduced by 32.1% compared with pure EP. Meanwhile, the addition of DPM‐H can partially solve the problem of the decrease of the EP mechanical property caused by the addition of APP. Compared with the flame‐retardant EP with the 8% loading of APP, the impact strength of EPDA‐2 increased 152.3%.