Single-phase 2-carboxyethyl(phenyl)phosphinic acid-modified Zr-MOFs as flame retardants for enhancing fire retardancy and smoke suppression of epoxy resins†

A 2-carboxyethyl(phenyl)phosphinic acid-functionalized metal–organic framework, CEPPA-UiO-67, was successfully synthesized through a post synthetic modification method, where CEPPA was coordinated onto the surface of UiO-67. When used as an additive flame retardant, CEPPA-UiO-67 enhanced the fire safety of epoxy resins. The EP/CEPPA-UiO-67 composite exhibited excellent flame retardancy and reduced toxic gas emissions. Compared with pure EP, the peak heat release rate and total smoke production of the EP/CEPPA-UiO-67 composite were reduced by 40.6% and 34.76%, respectively. Mechanistic studies indicated that the addition of CEPPA-UiO-67 altered the decomposition pathway of EP. Furthermore, the synergistic effect of CEPPA and UiO-67 promoted the formation of a dense carbon layer, which effectively slowed down the transfer of oxygen and heat, resulting in improved flame retardancy. This research provides valuable insights into the development of single-phase MOF-based flame retardants and their flame-retardant mechanisms.