Bioinspired Dopamine-Metal Coordination Coating of Polyphosphate Ammonium for Simultaneously Enhanced the Flame Retardancy and Mechanical Properties of Epoxy Resins

In this study, inspired by the adhesive proteins of mussels, a series of microencapsulated flame retardants M-DA@APP were prepared by coating ammonium polyphosphate (APP) with dopamine (DA) via coordination with metal ions, and then incorporated into epoxy resin (EP). The effects of these modifiers on the flame retardancy and mechanical properties of EP composites were systematically investigated. The results show that APP modified with Fe 3+ or Ni 2+ coordination exhibited excellent flame-retardant performance in EP. Specifically, the Fe-DA@APP/EP composite achieved a limiting oxygen index (LOI) of 30.1% and passed the UL-94V-0 rating. Cone calorimetry tests revealed that M-DA@APP significantly reduced the heat release rate, total heat release, and smoke production. The flame-retardant mechanism is mainly attributed to the metal-ion-catalyzed formation of a dense, highly graphitized char layer, which effectively insulates heat and oxygen. Moreover, owing to the improved interfacial compatibility between APP and the EP matrix enabled by the M-DA coating, the impact strength, tensile strength, and elongation at break of the composites were notably enhanced, overcoming the negative effect of conventional APP on mechanical performance. This work offers a promising strategy for developing efficient, environmentally friendly epoxy resin composites with superior flame retardancy and mechanical properties.