Synthesis of a novel phosphorus-containing melamine cyanurate derivative to enhance the fire resistance and mechanical properties of epoxy resin

The high flammability of epoxy resin (EP) greatly limits its application in industrial production. To enhance the fire resistance of EP, a phosphorus-containing melamine cyanurate derivative (P-MCA) flame retardant was synthesized by modifying melamine cyanurate (MCA) with phenylphosphonic dichloride (PPDCl). The structure and properties of P-MCA were comprehensively characterized. The EP composite with 5 wt% of P-MCA (EP/5 P-MCA) exhibited a limiting oxygen index of 29.2% and achieved a V-0 level in UL-94. Compared with EP, the peak heat release rate and peak smoke production rate of EP/5 P-MCA were reduced by 18.8% and 24.2%, respectively. The improved fire resistance of EP/5 P-MCA was attributed to the physical shielding of the carbon layer and the dilution effect of nitrogen-containing gases. Besides, the flexural strength of EP/5 P-MCA was 14.7% higher than that of EP due to the desirable compatibility of P-MCA and EP. Meanwhile, the glass transition temperature (Tg) of EP and the crosslinking density of the rubbery state increased to a certain extent with the addition of P-MCA. In conclusion, P-MCA can simultaneously improve the fire resistance and mechanical properties of EP, indicating great potential for application.