Novel ionic complex with flame retardancy and ultrastrong toughening effect on epoxy resin

The flammability and brittleness of epoxy resin (EP) restrict its application in advanced manufacturing. One promising strategy is to develop a flame retardant with high efficiency and enhanced toughness, but the existing preparation processes of flame retardants are complicated. In addition, these fire retardants have unsatisfactory efficiency and poor preservation of mechanical properties. In this work, a novel ionic complex was successfully synthesized via a facile neutralization reaction between methylphosphonic acid (MPA) and 1,10-diaminodecane (DAD). The complex, namely, MPA–DAD, is designed for use as a flame retardant and toughening additive for EP. Results show that 8 wt% MPA–DAD enabled EP to pass the UL 94 V-0 rating, with a 29 % limiting oxygen index, and greatly reduced the peak heat release rate and the total heat release, thus fulfilling the fire safety requirement in application. Additionally, as the ionic bonds resulted in a significant amount of dissipated energy and enhanced fracture toughness, the EP/8% MPA–DAD composite exhibited 1030 % and 611 % increases in tensile toughness and flexural toughness, respectively, and showed well-preserved strength. This work provides a facile fabrication route for high efficiency, multifunctional flame retardants for use in the manufacture of fire-safe, advanced EP composite materials.