Rationally Designed Flame-Retardant ZIF-67@γ-CD-MOFs@APP: An Integrated Hierarchical Nanostructure and Its Application in Polypropylene Towards Fire Resistance Enhancement

Metal–organic frameworks (MOFs) have great potential in improving the fire safety of polymer materials. To improve the fire resistance and smoke suppression of polypropylene (PP), a flame-retardant system ZIF-67@γ-CD-MOFs@APP incorporating multiple flame-retardant elements was designed and applied to PP. The coated PP passed UL-94 V-0 level with the LOI up to 36.2% and char residue of 12.47%. The PHRR, PSPR, COP, and CO 2 P of coated PP were reduced by 52.65%, 24.72%, 36.49%, and 52.29%, respectively, compared to neat PP. In addition, the tPHRR, tPSPR, tCOP, and tCO 2 P were prolonged by 405.3%, 345.4%, 427.8%, and 405.3% compared to pure PP, allowing more escape time when facing a real fire. Integrating the hierarchical porous structure provided by ZIF-67 and γ-CD-MOFs, catalytic carbonization of transition metal Co and the nitrogen-containing ligand, ZIF-67@γ-CD-MOFs@APP played a flame-retardant role both in the condensed and gas phase, endowing PP with enhanced flame retardancy and smoke suppression. The “all-in-one” strategy provides helpful insights for constructing fire retardant system with multi-level nanostructure.