The influence on flame retardant epoxy composites by a bird's nest-like structure of Co-based isomers evolved from zeolitic imidazolate framework-67

The machining of metal-organic frameworks (MOFs) based templates into diverse layered double hydroxides (LDHs) is essential to maximize their advantages in flame retardant polymers. However, improving the thermal stability of LDHs has so far continued to be a great challenge. Herein, a MOFs sacrificial template has been developed to realize the controlled synthesis of two Co-based isomers, namely CoCo-LDH and cobalt basic carbonate (CBC), with the construction of three different nanostructures of carbonate intercalated CoCo-LDH nanocage (LDH), single yolk@shell CBC@CoCo-LDH (s-CBC@LDH), and multi-yolk@shell CBC@CoCo-LDH (m-CBC@LDH). The thermal stability of CoCo-LDH is enhanced by controlling the reaction time. Moreover, CoCo-LDH from m-CBC@LDH decomposes at the right temperature while CBC nanoparticles further enhanced the flame retardancy. To demonstrate the high performance conjecture on the structure-property relationship, the as-synthesized Co-based isomers were individually integrated into the epoxy matrix to evaluate its comprehensive properties. Compared to LDH and s-CBC@LDH, m-CBC@LDH imparts superior thermal stability, flame retardancy, and comparable mechanical properties onto the epoxy composites. With the incorporation of 2 wt.% m-CBC@LDH, the peak of heat release rate and total heat release are decreased by 38.5% and 19.6%, respectively. This work provides a design direction for improving the flame retardant of epoxy resin.