Preparation of P/N/Si‐containing covalent organic framework‐based flame retardants and their application in epoxy resins

Abstract

Balancing the enhancement of flame retardancy of epoxy resin while maintaining its mechanical capacities intact poses a significant challenge in the realm of flame‐retardant epoxy resins. To reach the above objectives, a COF‐based synergistic flame retardant with phosphorus, nitrogen, and silicon (PA‐COF@MT) was synthesized using phytic acid (PA), montmorillonite (MT), and covalent organic framework (COF). When PA‐COF@MT was added at 4 wt%, EP/PA‐COF@MT exhibited a reduction of 42.1% in peak heat release rate (PHRR), 45.84% in total heat release (THR), and 59.8% in total smoke production (TSP) compared with the pure EP. LOI increased by 30.5% and UL‐94 tested to V‐0 grade. flame‐retardant index (FRI) value of 3.03, achieving a “good” rating. Fire growth indices and mean effective combustion heat were increased while mechanical properties also improved. These findings suggest that the flame retarding mechanism of PA‐COF@MT is mainly through vapor phase and condensed phase actions. The combined effects of phosphorus, nitrogen, and silicon make the surface of carbon residue solid and dense, resulting in excellent heat insulation and smoke suppression effects. In simple terms, this study provides new insights into COF‐based flame retardants. Combining low‐cost and simple preparation methods, PA‐COF@MT has broad application prospects in flame‐retardant epoxy resin systems.