A facile approach to prepare phosphorus and nitrogen containing macromolecular covalent organic nanosheets for enhancing flame retardancy and mechanical property of epoxy resin

The novel phosphorus and nitrogen containing covalent organic frameworks nanosheets, DOPO-COFs nanosheets have been synthesized through one step and then incorporated into epoxy resin (EP) by in situ polymerization. The successful preparation of DOPO-COFs nanosheets have been proved by vanishment of P-H group in FTIR curve of DOPO-COFs nanosheets, nano-size sheet with a lateral size of several micrometers in TEM image, and present of nitrogen and phosphorus elements in EDS pattern. The DOPO-COFs nanosheets show good dispersibility in EP matrix. The well-dispersed DOPO-COFs nanosheets contribute to thermal, mechanical, and flame retardant performances of EP. The weight loss rate of EP/3.2 wt% DOPO-COFs nanosheets decreases by 29.4%. The storage modulus (30 degrees C) and fracture strength of EP 4 increases by 64.5% and 15.6% compared with that of untreated one, respectively. The PHRR and THR of EP loaded with 3.2 wt% of DOPO-COFs nanosheets decrease by 18.4% and 18.50/0, respectively. The feasible mode of action for inhibiting fire hazard of EP nanocomposites has also been put forward.