Thermal Stability and Flame Retardancy of Epoxy Resin with DOPO-Based Compound Containing Triazole and Hydroxyl Groups

A reactive flame retardant (DTP) is successfully synthesized and characterized, and then incorporated into epoxy resin (EP) as a co-curing agent. The thermal stabilities and flame-retardant properties of epoxy thermosets are evaluated. Compared to neat EP, the thermogravimetric analysis (TG) results show that the thermal decomposition rate of EP/DTP is reduced by 45% and the char yield at 750 °C is increased by 67%, when the addition amount of DTP is 12 wt%. In the cone calorimetry test (CCT), the values of the peak of heat release rate (pk-HRR), total heat release (THR), total smoke produce (TSP), and average of effective heat combustion (av-EHC) of EP-DTP-12 are exhibited a reduction of 36.6%, 26.4%, 40.5%, and 23.6% relative to neat EP, respectively. Meanwhile, the value of the limiting oxygen index (LOI) of EP/DTP-12 can reach 34.83%, and 6 wt% or more loading of DTP make EP/DTP pass the V-0 rating in the UL-94 test. Moreover, the flame-retardant mechanism is investigated by thermogravimetric analysis/infrared spectrometry (TG-IR) and scanning electron microscopy (SEM), which can be summarized into two aspects: the quenching effect of phosphorus-containing radicals and diluting effect of nonflammable gases in the gas phase, and the barrier effect of char layer in the condensed phase.