Developing superior properties of epoxy resin composites with high fire resistance, light smoke, and low toxicity has been the focus of the research in the flame-retardant field. In particular, it is essential to decrease the emissions of toxic gases and smoke particles generated during the thermal decomposition of epoxy resin (EP) to satisfy the industrial requirements for environmental protection and safety. Consequently, the PZS@ZIF-67 composite was designed and synthesized by employing the hydroxyl group-containing polyphosphazene (poly(cyclotriphosphazene-co-4,4′-dihydroxydiphenylsulfone), PZS) as both the interfacial compatibility and an in situ template and the ZIF-67 nanocrystal as a nanoscale coating and flame-retardant cooperative. ZIF-67 nanocrystal with multidimensional nanostructures was uniformly wrapped on the surface of PZS microspheres. Subsequently, the acquired PZS@ZIF-67 composite was incorporated into the epoxy resin to prepare composite samples for the study of their fire safety, toxicity suppression, and mechanical performance. Herein, the EP/5% PZS@ZIF-67 passed the V-0 rating in a UL-94 test with a 31.9% limit oxygen index value. More precisely, it is endowed with a decline of 51.08%, 28.26%, and 37.87% of the peak heat release rate, the total heat release, and the total smoke production, respectively. In addition, the unique structure of PZS@ZIF-67 microsphere presented a slight impact on the mechanical properties of EP composites at low loading. The PZS@ZIF-67 possible flame-retardant mechanism was speculated based on the analysis of the condensed phase and the gas phase of EP composites.

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As a novel energetic material, 5-Amino-1H-tetrazole (5AT) has a history of proposed applications in the fields of airbags, rocket engines, and new propellants. However, the application of 5AT is limited for its poor combustion stability. Identification of the thermal behaviour and pyrolysis mechanism of 5AT could provide guidance on the control of combustion behaviour, which can be effectively improved by adding oxidizers. In this paper, five kinds of oxidizers (Ammonium perchlorate (AP), Sodium perchlorate (NaClO 4 ), Ammonium nitrate (AN), Manganese oxide (MnO 2 ), and Chromic oxide (Cr 2 O 3 )) are mixed with 5AT for investigating the catalytic effects of multi-type oxidizers on 5AT. Thermal behaviour is analysed by the TG-DSC test and the thermal activation energy is evaluated by Kissinger and Ozawa methods. Moreover, TG-FTIR and TG-MS analyses are used to infer the pyrolysis gas products of 5AT/oxidant. The experimental results indicate that the 5AT-AN has the lowest activation energy, and the degradation process was simplified into one step. The addition of AP, NaClO 4 , and MnO 2 can promote the pyrolysis process of 5AT due to the redox reaction between melamine and the decomposition products of oxidizers, while the catalytic effect of Cr 2 O 3 mainly occurs above 400 °C without the occurrence of oxidation. The catalytic mechanism of Cr 2 O 3 mainly performs on the polyaddition and the ring-opening reaction of N-containing heterocycles. The findings of this work may offer valuable direction for understanding, designing, and using 5AT-based propellants.