Flame-retardant properties and mechanisms of epoxy thermosets modified with two phosphorus-containing phenolic amines

Two phosphorus-containing phenolic amines, a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based derivative (DAP) by covalently bonding DOPO and imine (SB) obtained from the condensation of p -phenylenediamine with salicylaldehyde, and its analog (AP) via the addition reaction between diethyl phosphite and SB, were used to prepare flame-retardant epoxy resins. The burning behaviors and dynamic mechanical properties of epoxy thermosets were studied by limited oxygen index (LOI) measurement, UL-94 test, and dynamic mechanical analysis. The flame-retardant mechanisms of modified thermosets were investigated by thermogravimetric analysis, Py-GC/MS, Fourier transform infrared, SEM, elemental analysis, and laser Raman spectroscopy. The results revealed that epoxy thermoset modified with DAP displayed the blowing-out effect during UL-94 test. With the incorporation of 10 wt % DAP, the modified thermoset showed an LOI value of 36.1% and V-0 rating in UL-94 test. The flame-retardant mechanism was ascribed to the quenching and diluting effect in the gas phase and the formation of phosphorus-rich char layers in the condensed phase. However, the thermoset modified with 10 wt % AP only showed an LOI value of 25.7% and no rating in UL-94 test, which was possibly ascribed to the mismatching of charring process with gas emission process during combustion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 43953.