Composite Flame Retardant Based on Layered Double Hydroxide, Carbon Nanotubes, and Montmorillonite for Epoxy Resins

Epoxy resins (EPs) are widely employed on aircrafts as load-bearing structural materials, adhesives, and sealants due to their lightweight properties and corrosion resistance. However, owing to the inherent flammability of polymer materials, EPs are typically used after appropriate flame-retardant treatments. In this work, a triple in situ composite flame retardant of layered double hydroxide (LDH), carbon nanotubes (CNTs), and montmorillonite (MMT) is achieved via a one-pot strategy. The designed LDH–CNTs-MMT facilitates uniform dispersion of flame-retardant components within the polymer matrix, effectively mitigates the mechanical performance deterioration of the EP substrate typically induced by inorganic flame retardants, and improves the flame retardancy of EP/LDH–CNTs-MMT to a V-1 level in the UL-94 test and a limited oxygen index (LOI) of 31.0%. Notably, in combustion tests, the total heat and smoke releases of EP/LDH–CNTs-MMT are, respectively, reduced by 35.12% and 37.58% compared to those of untreated EP, which is critical for aircraft fire safety. Collaborative analyses of the char residue from EP/LDH–CNTs-MMT elucidate a synergistic flame-retardant mechanism enabled by the triple in situ composited components. This work will provide insights into the design of composite flame retardants for EP, thereby expanding its practical application on airplanes.