Synchronously enhanced flame retardancy and mechanical properties of epoxy/carbon fiber composites achieved via an interfacial structure design

Abstract

Carbon fiber (CF)–reinforced epoxy resin (EP) composites (E/C composites) have been widely used in numerous fields, but they are always plagued by the low flame retardancy because of the ‘candlewick’ effect of the CF. Although the conventional approach of adding flame retardants endows the composites with certain flame retardant capabilities, it impairs the mechanical properties of the composites. Herein, an interface structure design method was proposed, wherein polyphosphazene (PZS) nanoparticles were in situ synthesized on the surface of a CF to synchronously improve the flame retardancy and mechanical properties of E/C composites. After the incorporation of a few 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) particles into an epoxy matrix, the composite showed a limiting oxygen index (LOI) of 51.7, meeting the V-0 rating in the UL-94 testing. Moreover, compared with the blank E/C composite, the peak heat release rate (PHRR) was reduced by 51.1% and the total heat release (THR) decreased by 36.3%. Additionally, the tensile strength of the composites was boosted to 72.9 MPa, with an improvement rate of 40.7%. The mechanisms were mainly ascribed to the suppressed ‘candlewick’ effect by the interfacially distributed PZS nanoparticles, the strong hydrogen bonding interaction between components and the interfacial pinning effect of the rough CF surface. This work confirms the important role of interfacial structural design, and an appropriate interface structure can endow the E/C composites with good comprehensive performances.