Improving the flame retardancy and smoke suppression of epoxy resins by introducing of DOPO derivative functionalized ZIF-8

The introduction of traditional flame retardants into epoxy resins (EP) usually generated a number of harmful smoke during burning. A novel flame retardant (dZIF-8) was synthesized via functionalization of zeolitic imidazolate frameworks-8 by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives (DMZ). The flame retardancy and smoke suppression of the dZIF-8 modified EP were studied. The combustion results showed that dZIF-8 can effectively reduce the fire risk of EP. Compared with the neat EP, the value of peak heat release rate (PHRR), the total smoke release rate (TSRR) and the maximum smoke density of the EP containing 2% dZIF-8 were decreased by 51%, 47% and 36%, respectively. The TG-FTIR results showed that the production of the pyrolysis gaseous products was inhibited by dZIF-8 during the decomposition of EP. In addition, the synergistic effect between the DMZ and the zeolitic imidazolate frameworks-8 improved the flame retardancy of the EP. Meanwhile, the increase in the flame-retardant performance of the dZIF-8 modified EP was caused by the quenching effect of the free radical containing phosphorus in gas phase and the charring effect of pyrophosphoric acid and zinc oxide in condensed phase. The morphology of dZIF-8 crystal changed from granular to laminar, indicating that the introduction of DMZ affected the crystal growth of dZIF-8. The laminar structure of the dZIF-8 provided a layered barrier effect during the burning process of EP.