Surface functionalization of few-layer black phosphorene and its flame retardancy in epoxy resin

Abstract

Similar to graphene, single or few-layer of black phosphorus (BP) are promising for its high thermal stability and unique characteristic dimension effects. However, the agglomeration problem of BP nanosheets in polymer matrix renders great difficulty toward its application. Herein, Melamine-formaldehyde (MF) is conducted to functionalize black phosphorus (BP) nanosheets. Based on density functional theory (DFT) calculations, the adsorption energy is −0.63 eV, which suggests there exists a strong mutual adsorption between BP nanosheets and MF. The functionalized BP (BP@MF) is introduced into epoxy resin (EP) to evaluate its thermal stability and flame retardant properties. BP@MF can successfully solve the aggregation phenomenon due to the improved dispersibility of BP in EP matrix. With the incorporation of 1.2 wt% BP@MF into EP matrix, the char yield is dramatically improved by 70.9%, which is attributed to the outstanding thermal stability and the catalytic charring effect of BP@MF. EP/BP@MF nanocomposites can pass the UL-94V-0 rating, and the limiting oxygen index value increases by 25.9%. The peak of heat release rate is reduced by 43.3% and the fire growth rate decreases by 41.2%, which is ascribed to the inhibition of heat transfer and isolation of oxygen by BP@MF. Meanwhile, BP@MF reveals an extremely high flame retardant efficiency by a small addition amount. Below 400 °C, MF sublimates to absorb heat and BP@MF promotes the formation of an expanded carbon layer. Above 400 °C, BP may scavenge free radicals and catalyze char formation. As one new nanofiller of 2D materials, BP has great potential to fabricate high-performance nanocomposites.