Mechanically Reinforced Flame-Retardant Epoxy Resins by Layered Double Hydroxide In Situ Decorated Carbon Nanotubes

Epoxy resins (EPs) are widely used as structural materials in airplane compartments due to their lightweight merits and corrosion resistance. However, the flammability of polymers necessitates the exploration of high-performance flame retardants to improve aircraft fire safety. In this study, an in situ composite structure of layered double hydroxides (LDHs) and carbon nanotubes (CNTs) is constructed via a one-pot strategy in which LDH nanosheets are grown in situ on the skeleton of interwoven CNTs. The composite structure of LDH–CNTs acts as a mechanical support to further accommodate nanoparticles of 9,10-dihydro-9-oxa-10-phosphorus-10-oxide (DOPO) to obtain the flame retardant LDH–CNTs–DOPO. The in situ composite structure of LDH–CNTs realizes the uniform dispersion of the nanoscale flame-retardant components in the polymer substrate and endows the flame-retardant-treated EP substrate with both desirable mechanical strength and flame retardancy. Notably, the total heat release and smoke release of the flame-retardant composite EP@LDH–CNTs–DOPO are reduced by 19.0 and 25.56%, respectively, relative to those of neat EP, and a limiting oxygen index (LOI) of 31.0% and a flame-retardancy level of V-1 are achieved. A synergistic flame-retardant mechanism coordinated by LDH nanosheets, a supportive LDH–CNTs composite structure, and DOPO nanoparticles is proposed and elaborated by extensive fire-resistance evaluations and intensive analysis of the char residue after combustion.