Innovative design of hierarchical cobalt-based borate functionalized black phosphorus structure with petal-like wrinkle: Enhancing the fire safety and mechanical properties of epoxy resin

The weak anti-oxidation and smoke-suppression abilities limit the use of black phosphorus (BP) in the preparation of high-performance flame-retardant epoxy resin (EP) composites. Here, aromatic diazonium chemistry was used to graft phenylboronic acid on the surface of few-layer BP nanosheets (BPNSs) to obtain passivated BP based nanomaterials (BP-DPBA). Then, a novel multifunctional nano flame retardant BP-DPBA@Co-BO was obtained by anchoring amorphous cobalt-based borate (Co-BO) on the surface of BP-DPBA through a low temperature reduction reaction. Subsequently, BP-DPBA@Co-BO was incorporated into EP matrix in the form of nanofillers and formed a mechanically enhanced system. As expected, EP nanocomposites containing 2 wt% BP-DPBA@Co-BO achieves greatly improvements in thermal stability and fire safety, with 93% increase in char yield (CY) during pyrolysis, 48.4% and 41.7% decrease in peak heat release rate (PHRR) and total heat release (THR) during combustion respectively, a limiting oxygen index (LOI) value up to 32.5% and a UL94 rating of V0. In addition, the presence of Co-BO greatly improves the ability of BP to suppress toxic smoke. Specifically, EP/ BP-DPBA@Co-BO 2.0 achieves a 25.4% reduction in total smoke production (TSP) during combustion. In particular, the maximum 36.2% and 73.2% increases are achieved in storage modulus and impact strength, respectively, confirming that BP-DPBA@Co-BO can effectively enhance the mechanical properties of EP. Therefore, this work provides a feasible solution for loading high-valence metal compounds on the surface of BPNSs, and prepared high-performance EP nanocomposites with enhanced fire safety and mechanical properties.