A tryptamine-based DOPO derivative as a flame retardant for epoxy resins

A reactive flame retardant (HLD) is prepared for epoxy (EP) resin using tryptamine (PTM), 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO), and vanillin (VN) as reaction monomers. The effects of HLD on the thermal stability, mechanical characteristics, and flame resistance of the EP are evaluated. When 7 wt.% of HLD (only 0.43 wt.% of phosphorus) is added to pure EP, the thermal breakdown rate of the resulting EP/HLD7 composite is lowered by 28 %, and its coke output at 700 °C is raised by 45 %. In the cone calorimeter test (CCT), the peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and average effective thermal combustion (av-EHC) of the EP/HLD7 decrease by 52.1 %, 24.8 %, 25.1 %, and 34.0 %, respectively, compared to those of pure EP. A high limited oxygen index (31.86 %) and a V-0 rating in the UL-94 test are also achieved for EP/HLD7. The flame-retardancy mechanism is studied using thermogravimetric analysis/infrared spectroscopy (TG-IR) and scanning electron microscopy (SEM). The quenching effect of phosphorus-containing radicals, the dilution effect of noncombustible gases, and the impeding effect of the carbon layer in the condensed phase contributed collectively to the excellent flame-retardancy of EP/HLD7.