Carbon Fibers Decorated by Polyelectrolyte Complexes Toward Their Epoxy Resin Composites with High Fire Safety

The achievement of both robust fire-safety and mechanical properties is of vital requirement for carbon fiber (CF) composites. To this end, a facile interfacial strategy for fabricating flame-retardant carbon fibers decorated by bio-based polyelectrolyte complexes (PEC) consisting of chitosan (CH) and ammonium polyphosphate (APP) was developed, and its corresponding fire-retarded epoxy resin composites (EP/(PEC@CF)) without any other additional flame retardants were prepared. The decorated CFs were characterized by SEMEDX, XPS and XRD, indicating that the flame-retardant PEC coating was successfully constructed on the surface of CF. Thanks to the nitrogen- and phosphorous-containing PEC, the resulting composites exhibited excellent flame retardancy as the limiting oxygen index (LOI) increased from 31.0% of EP/CF to 40.5% and UL-94 V-0 rating was achieved with only 8.1 wt% PEC. EP/(PEC8.1@CF) also performed well in cone calorimetry with the decrease of peak-heat release rate (PHRR) and smoke production rate (SPR) by 50.0% and 30.4%, respectively, and the value of fire growth rate (FIGRA) was also reduced to 3.41 kW·m^–2·s^–1 from 4.84 kW·m^–2·s^–1, suggesting a considerably enhanced fire safety. Furthermore, SEM images of the burning residues revealed that the PEC coating exhibited the dominant flame-retardant activity in condensed phase via the formation of compact phosphorus-rich char. In addition, the impact strength of the composite was improved, together with no obvious deterioration of flexural properties and glass transition temperature. Taking advantage of the features, the PEC-decorated carbon fibers and the relevant composites fabricated by the cost-effective and facile strategy would bring more chances for widespread applications.