Imine bond-containing P/N/Si multi-element synergistic flame retardant: Endowing epoxy resin with excellent fire safety and mechanical enhancement

The improvement of mechanical properties and flame retardant performance of epoxy resin (EP) composites has long been a significant technical challenge. In this paper, using P/N synergistic flame retardation, a multicomponent flame retardant (DKD) containing imine bonds and silicon was developed by introducing imine bond structures and silicon elements. DKD brings excellent flame retardant properties to EP. The results demonstrated that the inclusion of just 5 wt% DKD enabled EP composites to attain a 29.7 % LOI and a UL-94 V-0 rating. Due to the introduction of large benzene rings and Si– O –Si cross-linking structures, DKD-3/EP's impact strength and DKD-7/EP's flexural strength increased by 15.6 % and 25 %, respectively, versus pure EP. In the CCT test, pure EP achieved a PHRR of 1075.0 kW/m 2 and a THR of 133.4 MJ/m 2 . The PHRR and THR of DKD-7/EP are 649.2 kW/m 2 and 81.1 MJ/m 2 respectively, which are 39.6 % and 39.2 % lower than the pure EP values. In addition, the TSP and SPR of DKD-7/EP decreased by 31.7 % and 24.2 %, respectively. Compared with pure EP, the CO and CO 2 production rates were reduced by 46.6 % and 50.0 %, respectively. Through the study on the flame retardant mechanism of DKD/EP, it was found that the addition of DKD generates dual flame-retardant effects in both the condensed and gas phases, thereby enhancing the fire safety of the EP system.