Joint flame-retardant effect of triazine-rich and triazine/phosphaphenanthrene compounds on epoxy resin thermoset

To obtain a more efficient flame-retardant system, the extra-triazine-rich compound melamine cyanurate (MCA) was coworked with tri(3-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-2-hydroxypropan-1-yl)-1,3,5-triazine-2,4,6-trione (TGIC-DOPO) in epoxy thermosets; these were composed of diglycidyl ether of bisphenol A (DGEBA) epoxy resin and 4,4-diaminodiphenyl methane (DDM). The flame-retardant properties were investigated by limited oxygen index measurement, vertical burning testing, and cone calorimeter testing. In contrast to the DGEBA/DDM (EP for short) thermoset with a single TGIC-DOPO, a better flame retardancy was obtained with TGIC-DOPO/MCA/EP. The 3% TGIC-DOPO/2% MCA/EP thermoset showed a lower peak heat-release rate value, a lower effective heat of combustion value, fewer total smoke products, and lower total yields of carbon monoxide and carbon dioxide in comparison with 3% TGIC-DOPO/EP. The results reveal that MCA and TGIC-DOPO worked jointly in flame-retardant thermosets. The dilution effect of MCA, the quenching effect of TGIC-DOPO, and their joint action inhibited the combustion intensity and imposed a better flame-retardant effect in the gas phase. The 3% TGIC-DOPO/2% MCA/EP thermoset also exhibited an increased residue yield, and more compositions with triazine rings were locked in the residues; this implied that MCA/TGIC-DOPO worked jointly in the condensed phase and promoted thermoset charring. The results reveal the better flame-retardant effect of the MCA/TGIC-DOPO system in the condensed phase. Therefore, the joint incorporation of MCA and TGIC-DOPO into the EP thermosets increased the flame-retardant effects in both the condensed and gas phases during combustion. This implied that the adjustment to the group ratio in the flame-retardant group system endowed the EP thermoset with better flame retardancy. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43241.