Boosting both flame retardancy and mechanical properties of carbon fiber/epoxy composites via polycyclic phosphorus-nitrogen imidazole derivative

[Display omitted] •A novel polyaromatic ring phosphor-nitrogen imidazole derivative (PNB) was designed and synthesized.•PNB could endow carbon fiber/epoxy resin composites with excellent flame retardancy and remarkable mechanical properties.•The flame retardant mechanism was analyzed and proposed. As a huge challenge to improve the mechanical properties while improving flame retardant performance in carbon fiber/epoxy resin composites. Hence, a novel flame retardant, polyaromatic ring phosphor-nitrogen imidazole derivative (PNB), was designed and used to prepare carbon fiber/epoxy composites (CF/EP-PNB). The optimal flame-retardant CF/EP-PNB composites exhibit excellent flame retardancy (the LOI of CF/EP-PNB composites with 10 % PNB could reach 33.8 % and pass V-0 grade in the UL-94 test and the residual chars could be as high as 70.7 %) and remarkable mechanical properties (the bending and impact strength of the CF/EP-PNB composites had increased by 41.5 % and 38.2 %, respectively).