Stepwise assembling manganese dioxide nanosheets and metal-organic frameworks on carbon fiber for deriving desirable mechanical properties and flame retardancy of epoxy composites

High fire hazard leads to an obstacle for the further application of carbon fiber (CF) reinforced epoxy resin (EP). Herein, a hierarchical structure consisting of manganese dioxide (MnO 2 ) nanosheets and UiO66-NH 2 was stepwise constructed on fiber surface. The obtained reinforcement imparted the composites with the desirable mechanical property and flame retardancy. The induced MnO 2 nanosheets and UiO66-NH 2 significantly enhanced the surface roughness and the active groups of fiber surface. As a result, the flexural strength and impact strength of CF/MnO 2 /UiO66-NH 2 epoxy composites were dramatically increased by 50.9% and 23.8% compared with that of untreated CF composite. Moreover, this hierarchical reinforcement presented 54.99% and 78.65% reduction in peak heat release rate (PHRR) and total heat release (THR) in contrast to untreated CF, respectively, indicating the good flame retardancy. The analysis on the results of con calorimetry test and the char residue certified that the MnO 2 nanosheets and UiO66-NH 2 can act as a physical barrier and catalyze the formation of a dense char layer to hinder the heat and the smoke release. This work proposes an effective strategy toward excellent mechanical properties and desired flame retardancy that could offer new ideas for high-performance resin matrix composites manufacturing. Graphical abstract CF/MnO 2 /UiO66-NH 2 epoxy composite with desirable mechanical property and flame retardancy was prepared by stepwise assembling MnO 2 nanosheets and UiO66-NH 2 on CF.