Mechanistic Insights Into Defect‐Engineered Carbon Nanohorns Reinforcing Mechanical Properties and Flame Retardancy of Epoxy Nanocomposites

ABSTRACT While single‐walled carbon nanohorns (SWCNHs) are known for mechanical reinforcement, their potential in flame‐retarding epoxy resin (EP) remains underexplored. In this work, defect‐engineered SWCNHs (oSWCNHs) obtained through controlled oxidation were incorporated into EP to investigate their influence on mechanical behavior, thermal stability, and flame retardancy. Both pristine SWCNHs and oSWCNHs significantly increased the storage modulus, cross‐linking density, Young's modulus, and tensile strength of the epoxy matrix. At an optimal loading of 0.15% oSWCNHs, the tensile strength of EP increased from 50.2 ± 3.5 to 74.5 ± 3.8 MPa, whereas higher contents led to a decline in performance. Crucially, flame retardancy improved notably, with the limiting oxygen index (LOI) value rising from 25.4% ± 0.2% to 28.5% ± 0.1% and the peak heat release rate (pHRR) decreasing from 802 to 600 W/g. Mechanistic analysis revealed that abundant defect sites in oSWCNHs enable strong gas‐phase OH˙ radical scavenging, while concurrently promoting higher cross‐linking density and thermal conductivity of the nanocomposites. This work highlights defect‐engineered SWCNHs as multifunctional nanofillers capable of enhancing both the mechanical and flame‐retardant performance of epoxy nanocomposites.