Functionalized ammonium polyphosphate flame retardant with covalent anchoring strategy for epoxy resin with triple functions of flame retardancy, smoke suppression and char formation

In order to solve the char formation and smoke suppression problems of ammonium polyphosphate (APP) in epoxy resin (EP) systems, this research synthesized flame-retardant SPFE using silane coupling agent KH550, which utilizes the hydrolytic condensation of the silane coupling agent to achieve covalent bonding with the surface of APP, and anchors ferrocene in the structure of the Schiff base. Applying SPFE to EP gives EP the triple functions of flame retardant, smoke suppression and char formation. It was demonstrated that the addition of SPFE improved the EP system's flexural and impact strength, mainly due to the effect of the introduction of the Schiff base group and the rigid large benzene ring on the crosslinking density of the system. By analyzing the fire safety behavior of the system, 3 wt % of SPFE can make the EP system UL-94 rating V-0. In the CCT test, pure EP has a peak heat release rate (PHRR) that up to 1075.1 kW · m -2 , and the total heat release (THR) is as high as 131.3 MJ · m -2 . EP/3-SPFE can reduce the system PHRR and THR by 47.3 % and 34.7 %, respectively. Attributed to the presence of ferrocene, EP/3-SPFE decreased the total smoke release (TSR) and smoke release rate (SPR) of the system by 41.6 % and 34.9 %, respectively, while promoting the conversion of CO to CO 2 in the system. According to research on its flame retardant mechanism, the addition of SPFE can significantly improve the quality of the char layer while also diluting the flammable gases produced during combustion. It also has a dual-phase flame retardant effect in the gas phase and condensed phase, increasing the EP's fire safety.