ZIF-67-derived CuCo-layered double hydroxide/ammonium polyphosphate hybrid for highly efficient flame retardant epoxy resin via synergistic catalytic carbonization

Ammonium polyphosphate (APP) has been commonly used as a commercial flame retardant. However, its application to flame-retardant epoxy resins (EP) has been faced with the problems of high smoke generation and degradation of mechanical properties. This has greatly limited its wide application in the field of building materials. In this work, a highly efficient flame retardant APP@M-LDH was prepared by using ZIF-67 as a bridge, and its microstructure, chemical composition, and thermal stability were comprehensively characterized. Due to the synergistic flame retardant effect of APP and LDH and the catalytic oxidation of copper and cobalt ions in the LDH structure in the gas phase, the peak heat release rate (PHRR), total heat release rate (THR) and total smoke release rate (TSP) of EP/4APP@M-LDH were reduced by 34 %, 35.3 % and 40.3 %, respectively, which achieved the high efficiency of flame retardancy for EP. In addition, due to the three-dimensional structure of the synthesized CuCo-LDH, which can expose more hydrogen bonds, the flexural strength and flexural modulus of EP/4APP@M-LDH were significantly increased by 54.1 % and 63.6 %, respectively. This study provides new ideas for the design of efficient flame retardants for EP.