Natural halloysite nanotubes decorated with organophosphorous for highly flame‐resistant epoxy composites

Abstract Highly flame‐resistant epoxy composites have important application value in many industrial fields. Unfortunately, epoxy resins (EPs) are inherently flammable materials and exhibit great fire hazard. In this study, the commercially available 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was chemically immobilized on the surface of natural halloysite nanotubes (HNTs) via the linkage of vinyltrimethoxysilane to obtain a novel flame‐retardant VD@HNTs containing P/Si/Al elements. It was found that the flame‐retardant VD@HNTs can effectively improve the thermal stability and flame resistance of epoxy composites. Typically, when 10% of VD@HNTs is added in EP, the limiting oxygen index of as‐prepared VD@HNTs/EP composites reaches 30.3%, and it also successfully reaches V‐0 classification in the UL‐94 test. Besides, the ignition time of VD@HNTs/EP composites was enhanced from 42 s for pure EP to 60 s, and the maximum heat release rate was reduced from 1221 to 758 kW∙m −2 . These great findings promise an innovative and efficient strategy for improving the fire safety of EP products and may also offer valuable insight toward fabricating various novel organic–inorganic flame retardants as well as highly flame‐resistant polymer composites. Highlights A novel flame‐retardant VD@HNTs containing P/Si/Al elements was prepared by the chemical decoration of HNTs with organophosphorous. The VD@HNT can effectively improve the thermal stability and flame resistance of epoxy composites. Synergistic flame‐retardant mechanism of phosphorus‐based flame retardants and natural HNTs was classified.