Integrated effect of NH<inf>2</inf>-functionalized/triazine based covalent organic framework black phosphorus on reducing fire hazards of epoxy nanocomposites

As the most thermodynamical and chemical stable allotrope of phosphorus, black phosphorus (BP) has recently generated huge research interest due to its high carrier mobility, semi-conductive property and an intrinsically tunable bandgap. BP has shown potential application in flame retardant polymer nanocomposites as emerging nanofiller. However the utilization of BP in polymer nanocompsoites still remains a huge challenge as it is prone to oxidation in water under air condition and pristine BP shows limited flame retardancy efficiency. In order to solve these issues, herein, triazine based organic framework was grown onto the surface of two-dimensional (2D) BP by in situ polymerization, resulting in the formation of organic-inorganic hybrids (BP-NH-TOF) which were subsequently incorporated into epoxy resin to fabricate the final nanocomposites. With increasing the loading of BP-NH-TOF in EP nanocomposites, the corresponding PHRR, THR, TSR and SPR values were reduced remarkably. For example, the addition of 2 wt% BP-NH-TOF results in a maximum decrease in PHRR (61.2%) and THR (44.3%) along with the dramatically improved LOI (29.0%) and UL-94 (V-0) performance, in addition to the obvious reduction of the amount of toxic carbon monoxide and flammable volatile products. Meanwhile, the mechanical properties of EP/BP-NH-TOF nanocomposites are enhanced significantly, e.g. 67.1% improvement in storage modulus at 1 wt% of BP-NH-TOF loading along with the improved glass transition temperature. The outstanding fire safety and mechanical properties of EP nanocomposites are attributed to the synergistic action of BP-NH-TOF hybrids. This work provides a facile method to prepared functionlized BP with the application in high performance flame retardant polymer nanocomposites.