Enhancing flame retardancy and mechanical properties of epoxy/carbon fiber composites via a metal-phosphorus synergistic interface structure

Carbon fiber (CF)-reinforced epoxy resin (EP) (E/C) composites are widely used in many fields, but their flame retardancy is usually low due to the “wick effect” of CF. Although interfacial self-catalysis can improve the flame retardancy of composites, the flame retardant efficiency remains low and the mechanical properties require optimization. This work proposed a novel method of assembling polyphosphazene (PZS) and zeolitic imidazolate framework-8 (ZIF-8) on the CF surface to synchronously enhance the flame retardancy and mechanical properties of E/C composites. With the aid of a small amount of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) in EP matrix, the limit oxygen index (LOI) was enhanced to 45.1 % and the V -0 standard in UL-94 testing was also achieved. Compared to the blank E/C composite, the peak heat release rate (PHRR) and the total heat release (THR) decreased by 57.1 % and 47.0 %, respectively, while the tensile strength increased to 100.1 MPa, corresponding to an improvement rate of 102.2 %. The mechanisms were mainly attributed to the inhibition of the “wick effect” of CF by PZS and ZIF-8, the strong hydrogen bonding interaction between components, and the interfacial pinning effect of the rough CF surface. This work provides new interfacial structure design method for CF reinforced EP composites with great potential applications in many fields ranging from railway vehicles, new energy automobiles, aircrafts to energy and industrial equipment.