Aromatic P/N/Co-containing microsphere flame retardant for enhancing fire safety and mechanical properties of epoxy coating with lower curing temperature

Improving fire safety performance is one of the most important measures to expand the application field of epoxy resin (EP) coatings. In this work, a novel aromatic phosphorus/nitrogen/cobalt-containing microsphere flame retardant (FNP-Co) was synthesized via a solvothermal method and proposed for fabricating high-performance EP coatings. EP coatings containing FNP-Co exhibited not only remarkable fire safety performance but also enhanced mechanical properties and lower curing temperature. The differential scanning calorimetry (DSC) test demonstrated that FNP-Co endowed EP/FNP-Co coatings with lower curing temperatures compared with that of pure EP, which was conducive to the processing of EP coatings. Furthermore, with incorporating 4 wt% FNP-Co, the limiting oxygen index (LOI) of EP coating (EP/4FNP-Co) was increased to 30.2 %. And the peak heat release, peak smoke production, and peak CO production rate of EP/4FNP-Co were reduced by 19.85 %, 36.3 %, and 34.18 %, respectively, compared with those of pure EP. It has been found that FNP-Co promoted the formation of a honeycomb-like and compact char layer for EP/FNP-Co coatings during combustion, which could play a "labyrinth effect" and barrier effect to prohibit the heat and pyrolysis gas transfer. Moreover, the flexural strength and flexural modulus of EP/4FNP-Co were enhanced by 2.9 % and 32.5 % compared with those of pure EP. The unique microsphere structure and synergistic effect of ternary flame-retardant elements of FNP-Co were responsible for the desirable integrated properties of EP coatings. Therefore, this novel microsphere flame retardant can impart EP/FNP-Co coatings with a broad application in the coating field.