Simultaneous enhancement of thermal conductivity and flame retardancy for epoxy resin thermosets through self-assemble of ammonium polyphosphate surface with graphitic carbon nitride

Conferring the flame retardant performance and thermal conductivity simultaneously for epoxy resin (EP) thermosets was significant for fire safety and thermal management applications of electrical and electronic devices. Herein, the graphitic carbon nitride (g-C3N4) with desired amount was assembled on the surface of ammonium polyphosphate (APP), and the obtained APP/g-C3N4 (CN-APP) was characterized and confirmed by X-ray diffraction, Fourier transform infrared spectroscopy tests, scanning electron microscopy, and transmission electron microscopy. CN-APP was incorporated into EP and then cured with m-phenylenediamine. The thermal conductive value of EP/CN-APP thermosets achieved 1.09 W center dot mK(-1), and the samples achieved UL-94 V-0 grade during vertical burning tests with the limiting oxygen index of 30.1% when 7 wt% CN-APP with the mass fraction of APP/g-C3N4 of 9/1 was incorporated. For comparative investigation, equal amount of individual g-C3N4 was introduced into EP thermosets, and the thermal conductivity was only 0.4 W center dot mK(-1). Compared with pure EP, the addition of CN-APP enhanced the glass transition temperature of EP/CN-APP thermosets and promoted the generation of more expanded, coherent, and compact char layer during combustion. Consequently, the heat release and smoke production of EP/CN-APP thermosets were greatly suppressed and led to the improvement of fire safety of materials. It was an alternative and promising approach for preparing high-performance polymeric materials especially used in integrated electronic devices.