Well-Designed Flame Retardants for Epoxy Resin Composites That Simultaneously Improve Heat Resistance, Mechanical Properties and Fire Safety

Epoxy resin (EP) flammability severely limits its application in some industrial fields, while flame retardant epoxy resin (FREP) often suffers from the problem of not being able to balance flame retardant properties with mechanical properties. To solve the problem, in this work, HDP, a reactive flame retardant was succeeded in synthesizing by the one-pot method using protocatechuic aldehyde (PH), 2,4-diamino-6-phenyl-1,3,5-triazine (DPT), and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as reactive monomers, was used to improve the flame retardancy of EP. And evaluated the effect of HDP on the curing reaction, heat resistance and mechanical property of EP. The introduced of four phenolic hydroxyl groups and two secondary amine groups enhanced the compatibility of the flame retardant HDP in EP and improved process performance. The apparent activation energy (Ec) was reduced by 8.1%, facilitating the curing of EP/DDM. When 5wt% of HDP (with only 0.36wt% phosphorus content) was added to EP, the flexural strength and modulus of FREP increased by 21.0% and 14.9%, respectively, and the Tg increased by 9.0% compared to EP. Cone calorimeter test (CCT) data showed that compared to EP, samples of EP/HDP-5 showed a 14.5% and 21.6% reduction in total heat release (THR) and total smoke production (TSP), respectively, and a 13.7% increase in coke yield (CY). EP/HDP-5 has a high limited oxygen index (32.5%) and passes the UL-94 V-0 classification. The excellent char formation and flame retardancy was owed to the dual role of the condensed and gas phases of FREP in the combustion process.