Hierarchical Nanospheres toward Flame-Retardant, Mechanically Strong, and Low-Toxicity Epoxy Resins

To endow epoxy resins (EPs) with outstanding flame-retardant and smoke-inhibiting effects, a multifunctional nanoparticle (SCP) has been designed and prepared via a simple approach, wherein Cu2O, melamine, and phosphorus-containing flame retardants were successively deposited onto the surface of silica nanospheres. The incorporation of a low addition amount of 2 wt % SCP within the EP demonstrates a significant improvement in flame retardancy. This enhancement is evidenced by a notable increase in the limiting oxygen index to 29.2% and attainment of a V-1 rating in the vertical burning test, in contrast to the respective values of 23.8% and no rating for unmodified EP, respectively. Moreover, the total smoke production, peak of heat release rate, and peak production rate of CO of EP/SCP-2 during the cone calorimeter test decreased by 10.2%, 26.1%, and 37.0%, respectively. Besides, the incorporation of 2 wt % SCP also endows the EP composites with commendable mechanical properties and glass transition temperature (Tg), as evidenced by a 22.5% increase in impact strength, an 8.1% rise in tensile strength, and a 9.5% increase in Tg, comparing with the unmodified EP. The flame-retardant mechanism analysis revealed that SCP functions within epoxy resin through both gas-phase and condensed-phase mechanisms. Overall, the proposed multifunctional nanoparticle strategy presents promising approaches for simultaneously enhancing the fire safety and mechanical performance of polymer materials.