Benefiting from the multiple effects of ferrocene and cyclotriphosphazene bi-based hierarchical layered nanosheets towards improving fire safety and mechanical properties of epoxy resin

Epoxy resin (EP) is widely used in automobiles, aerospace, electrical and electronic fields. However, the overloading of flame retardant will heavily deteriorate the mechanical properties of EP. In this paper, flame retardant nanosheets (FH) with hierarchical layered structure was self-assembled by combining ferrocene formaldehyde (Fc-CHO) and hexa-aminophenoxy-cyclotriphosphazene (HACP) through a nucleophilic reaction. The limiting oxygen index (LOI) of the EP/FH2 nanocomposite with a 2 wt% loading of FH increased to 31.3% and the UL-94 V-0 rating was achieved due to the multiple synergistic flame retardant effects between ferrocene and cyclotriphosphazene, as well as the barrier performance of the FH nanosheets. Simultaneously, in the cone calorimeter (CC) test, the peak heat release rate (pHRR) and total smoke production (TSP) were reduced by 30.2% and 19.0% compared with EP, respectively. What's more, toughness of the EP/FH2 nanocomposite were greatly improved owing to the low loading and good compatibility of FH nanosheets in EP. In short, this work provides valuable insights into the design of flame retardant nanosheets and targets to balance the flame retardancy and mechanical properties of EP with low addition amounts.