Modification of diatomite with melamine coated zeolitic imidazolate framework-8 as an effective flame retardant to enhance flame retardancy and smoke suppression of rigid polyurethane foam

In this work, the core-shell structure (ZIF-8@MA) was prepared first with melamine (MA) coated zeolitic imidazolate framework-8 (ZIF-8), and the ternary composite ZMD containing Si-N-Zn was successfully synthesized with the diatomite modified ZIF-8@MA. Subsequently, the prepared ZMD was added into rigid polyurethane foam (RPUF) to investigate its effect on fire safety of RPUF. The results of cone calorimeter and limiting oxygen index (LOI) tests indicated that ZMD effectively reduced the fire hazard of RPUF. This was because of the physical barrier effect of diatomite, the co-catalyzed char formation in the condensed phase of ZnO produced by the decomposition of ZIF-8 and silica produced by the decomposition of diatomite, and the gas phase effect of MA that enabled RPUF to achieve excellent flame retardancy and smoke suppression. The specific mechanism of flame retardancy and smoke suppression of ZMD for RPUF was also discussed in this study.