(751f) Effects of Zeolitic Imidazolate Frameworks (ZIFs) on Fire Behaviors of Intumescent Flame-Retarded Polypropylene (PP) Composites

As an efficient halogen-free compound, the intumescent flame retardants (IFRs) have gradually been commercialized and widely used in industries for a fire-safe polymeric composite. However, there are still some challenges for IFRs, such as poor stability and low dispersion efficiency in the polymer matrix. A combination of conventional IFRs with metal organic frameworks (MOFs) is a promising strategy to develop well-dispersed and highly efficient flame-retarded polymer nanocomposites. In this work, ZIF8-IFR-PP polymeric nanocomposites were synthesized, characterized, and followed by various fire testing. It was found that when adding 2 wt% ZIF-8, the peak heat release rate was decreased to 172.90 kW/m² compared with 298.30 kW/m² for IFR-PP and 904.98 kW/m² for neat PP. ZIF-8 nanocomposite also shows an excellent smoke suppression. A reduction of total smoke release was observed from 2704.2 m²/m² to 1886.2 m²/m² and peak smoke production rate decreased from 0.10 m²/s to 0.045 m²/s. Another released toxic component CO production rate were also suppressed during the combustion period. The reasons for these improvements are ascribed to a synergistic effect between IFR and ZIF8 on promoting cross-linking reaction in the condense phase for a carbonaceous physical barrier. Different metal irons (ZIF67) and bimetal ZIFs (ZnCo-ZIF) were also synthesized to further investigate how metal iron compositions affect the fire safety performance of ZIF-IFR-PP nanocomposites. Interestingly, it was found that ZIF67 has promoted more stable crosslinking components than ZIF8, which leads to a more compact and continuous char structures. CO production rate during the combustion was further decreased in ZIF67 and ZnCo-ZIF nanocomposites compared with ZIF8 nanocomposite due to the catalytic oxidation process from the cobalt. Overall, with a small loading (2%) ZIFs in IFR-PP, it can remarkably reduce the flammability and toxicity during the polymer combustion, including heat release rate, smoke production, and CO production rate. Therefore, the fabrication of MOFs together with conventional flame retardants provide new opportunities on developing novel fire-safe polymeric composites.