Tuning the polycondensation of phosphazenes with ZIF-67 and its effects on UV/fire resistant epoxy composites

Abstract

Zeolite imidazole salt frame (ZIF-67) has a highly regular microporous structure, large specific surface and certain flame retardant properties, and 2-methylimidazole in it is very sensitive to protolation reaction, so ZIF-67 can be etched to get more properties. However, different etching methods often yield different results. So we use H⁺ produced by the synthesis of 2-aminopyrazine and hexachlorophosphazene (HCCP) to directly or synchronously etch ZIF-67. Two kinds of flame retardants with sugar-frosting structure and fig-like structure with UV shielding capability are designed and synthesized, and the two etching methods are compared. When 2.0 wt% flame retardant is added to epoxy resin system, the total heat release rate of EP/AHCTP epoxy composite is reduced by 29.4 %, the peak heat release rate of EP/CHCTP composite is reduced by 38.5 %, and the CO and CO₂ production of EP/CHCTP composite are reduced by 45.2 % and 40.1 %, respectively. The UV shielding performance is improved while the mechanical properties are maintained. In the background of the rapid development of MOFs modification research, we compare two methods of binding ZIF-67 with small molecule phosphazenes and suggest its potential application in flame retardancy and UV resistance of EP.