Heterogeneous ZIF-67@MMT with catalytic effect inhibits CO release: Application of mismatch engineering design based on lotus leaf inspiration in flame retardant and toughening of polypropylene

The synthesis of a multifunctional flame retardant that combines flame retardancy, smoke suppression, and toughening effects is essential for expanding the range of applications for polyolefins. Inspired by the superhydrophobicity and low surface energy due to the lotus leaf micro/nano hierarchical structure, in this paper, we constructed 2D-3D heterogeneous ZIF-67@MMT by growing ZIF-67 in situ on the surface of montmorillonite (MMT) layers using wet chemistry. Mismatch engineering and micro/nano-graded heterogeneous structure confer high dispersibility and a high specific surface area on MMT, thus optimizing the pore structure and catalytic activity. Polypropylene (PP) composites with 25 wt% intumescent flame retardant (IFR) and 3 wt% ZIF-67@MMT achieved a 32.1 % limiting oxygen index and a UL-94 V-0 rating. 3ZIF-67@MMT/IFR/PP showed a 93 %, 86 %, and 66 % reduction in peak heat release rate, total smoke production, and CO production, respectively. In addition, ZIF-67@MMT has good interfacial compatibility and mechanical interlocking with PP. The tensile strength and elongation at break of 3ZIF-67@MMT/IFR/PP were increased by 58 % and 64 %, respectively, compared to 2MMT/IFR/PP. This work provides an effective strategy for the design of multifunctional heterogeneous nanomaterials for fire safety and other potential applications.