Synthesis of modified illite coated with melamine and aminotrimethylene phosphonic acid and study on its flame-retardant properties for epoxy resin

Epoxy resin (EP) is a high-performance polymer whose broader application is restricted by inherent flammability. In this work, a novel core-shell ILA@ATMEL was synthesized by coating natural illite with melamine-based aminotrimethylene phosphonate (ATMEL). The resulting hybrid was incorporated into EP to simultaneously improve flame retardancy and mechanical properties. With the addition of 9 phr ILA@ATMEL, the limiting oxygen index of EP composite reached 28.8 %, and the char residue at 800 °C increased from 17.82 % to 29.57 %. Cone calorimetry tests revealed notable reductions in peak heat release rate (33.57 %), total heat release (20.89 %), peak smoke production rate (29.37 %), and total smoke production (14.17 %) compared to those of pore EP. These improvements are attributed to synergistic flame-retardant mechanisms both in the condensed phase and the gas phase with Si, Al, P, and N elements. Moreover, ILA@ATMEL acts as a reinforcing filler at low loadings. The composite with 3 phr additive exhibited increases in elongation at break and tensile strength by 10.57 % and 18.86 %, respectively. This study demonstrates a feasible strategy for designing eco-friendly, high-performance EP composites with enhanced fire safety and mechanical durability via mineral-based core-shell flame retardants.