Gas-phase flame-retardant effects of a bi-group compound based on phosphaphenanthrene and triazine-trione groups in epoxy resin

A flame retardant TAD constructed by phosphaphenanthrene and triazine-trione groups was synthesized via addition reaction between triallyl isocyanurate (TAIC) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Then, the molecular structure and thermal stability of TAD were characterized. To research its flame-retardant behaviors, TAD was incorporated into epoxy resin, diglycidyl ether of bisphenol-A, cured by 4,4′-diamino-diphenyl sulfone (DDS). TAD obviously increased the LOI values and UL94 rating of epoxy resin thermosets. TAD also reduced the values including peak of heat release rate (pk-HRR), total heat release (THR), average effective heat of combustion (av-EHC), average CO₂ yield and total mass loss (TML), and increased average CO yields of epoxy thermosets. Further, the different decrease ratio of av-EHC and TML from thermoset containing TAD reveals that TAD exerted more gas-phase flame-retardant effect than condensed-phase effect. The opinion also was testified by the TAD/EP residues with loosen morphology from the cone calorimeter test. The analyzed pyrolysis route of TAD reveals that phosphaphenanthrene group mainly exerted quenching effect and the triazine-trione group exerted gas dilution effect. The excellent flame-retardant performance of TAD is resulted by the group synergistic effect from the two typical flame-retardant groups: phosphaphenanthrene and triazine-trione.