Functionalized halloysite nanotubes endowing epoxy resin with simultaneously enhanced flame retardancy and mechanical properties

In order to impart epoxy resin (EP) with desired flame retardancy, thermal stability and mechanical properties, a novel flame retardant HNT@PZM@Fe(OH) 3 with hierarchical core–shell-dot structure was successfully constructed in this work. The shell layer composed of polyphosphazene (PZM) effectively facilitated the interface interaction between halloysite nanotube (HNT) and polymer matrix, and significantly reinforced the EP nanocomposites (26.6 % increase in tensile strength and 31.5 % increase in impact strength when introduced with 5 wt% HNT@PZM@Fe(OH) 3 ). Owing to the interfacial catalysis of transition metal compounds and barrier effect of HNT, EP/HNT@PZM@Fe(OH) 3 performed remarkably in flame retardancy and smoke suppression. Upon the incorporation of 5 wt% HNT@PZM@Fe(OH) 3 , EP nanocomposites possessed the limiting oxygen index (LOI) of 30.8 %, reaching UL-94 V-0 rating. Cone calorimeter tests proved a distinct fall in the peak of heat release rate (PHRR) and smoke production rate (SPR) of EP/5HNT@PZM@Fe(OH) 3 , being respectively 65.8 % and 57.1 % compared to EP. The relevant tests revealed that the interfacial charring catalysis of transition metal oxides was beneficial to the formation of residual char structure with higher graphitization degree, which further improved the fire safety. Our work has provided a   research basis   and promising prospect for the production of high-efficient flame retardant EP nanocomposites.