Synchronously Enhanced Flame Retardance and Mechanical Properties of Epoxy/Carbon Fiber Composites Achieved by Interfacial Structure Design†

Abstract

Carbon fiber (CF) reinforced epoxy resin (EP) composites (E/C) have been widely used in numerous fields, but they are always plagued by the low flame retardancy because of the ‘candlewick’ effectof CF. Although the conventional approach of adding flame retardants enables the composites to obtain certain flame retardant capabilities, it impairs the mechanical properties of the composites. This work put forward an interface structure design method, specifically, in-situ synthesizing polyphosphazene (PZS) nanoparticles on the surface of CF to synchronously improve the flame retardance and mechanical properties of E/C composites. By incorporating a few 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) in 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 to 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 interfacial distributed PZS nanoparticles, the strong hydrogen bonding interaction between components and the interfacial pinning effect of rough CF surface. This work confirms the important role of interfacial structural design and the appropriate interface structure can endow the E/C composites with good comprehensive performances.