Synthesis of a Reactive Template-Induced Core–Shell PZS@ZIF-67 Composite Microspheres and Its Application in Epoxy Composites

Abstract

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.

Precise Control of a Yolk-Double Shell Metal–Organic Framework-Based Nanostructure Provides Enhanced Fire Safety for Epoxy Nanocomposites

“…29 When ZIF was covered by PZS, the decomposition occurred earlier between 281 and 553 °C and was caused by the poorer thermal stability of PZS versus ZIF followed by a delayed stage similar to ZIF starting at 671 °C. 30 The first stage from 183 to 296 °C for ZIF@LDH@PZS was ascribed to the release of water, and the second stage with the third peak was the same as ZIF@PZS except for the destruction of LDH. 31 However, LDH@PZS@NH underwent a rapid decrease in weight before 300 °C, which was affected by the unstable NH on the outer layer.…”

“…The slow mass loss of ZIF during the first stage corresponded to the absorbed water in the system, and the main decomposition temperature ranged from 460 to 587 °C because of the collapse of the coordination structure . When ZIF was covered by PZS, the decomposition occurred earlier between 281 and 553 °C and was caused by the poorer thermal stability of PZS versus ZIF followed by a delayed stage similar to ZIF starting at 671 °C . The first stage from 183 to 296 °C for ZIF@LDH@PZS was ascribed to the release of water, and the second stage with the third peak was the same as ZIF@PZS except for the destruction of LDH .…”

Hollow Nanospheres of Red Phosphorus for Fireproof Flexible Sensors Fabricated via 3D Printing

“…Figure b demonstrates the thermal stability for TPU-CNTs/RPHN. A sensor with integrated RPHNs presents the initial decomposition temperature (i.e., the temperature corresponding to 5% weight loss, T 5% ) of 226.4 °C, which is mainly caused by the cleavage of the side groups of organic molecules and the decomposition of additives (Figure c) . Furthermore, the mass for TPU-CNTs/RPHN decreases rapidly at 300–400 °C, and the maximum thermal decomposition temperature (i.e., the temperature corresponding to the maximum decomposition rate, T max ) is 355.1 °C.…”

“…A sensor with integrated RPHNs presents the initial decomposition temperature (i.e., the temperature corresponding to 5% weight loss, T 5% ) of 226.4 °C, which is mainly caused by the cleavage of the side groups of organic molecules and the decomposition of additives (Figure 5c). 34 Furthermore, the mass for TPU-CNTs/RPHN decreases rapidly at 300−400 °C, and the maximum thermal decomposition temperature (i.e., the temperature corresponding to the maximum decomposition rate, T max ) is 355.1 °C. The heat released by the decomposition of the matrix accelerates the oxidation of RPHNs and decomposes into high-activity phosphorus species (for example, phosphoric acid), 35 followed by conversion to polyphosphate, which promotes the dehydration of oxygen-containing molecular chains and further accelerates the formation of a char layer.…”

Surface Functionalization of Black Phosphorus via Amine Compounds and Its Impacts on the Flame Retardancy and Thermal Decomposition Behaviors of Epoxy Resin

“…Epoxy resin (EP), an important thermosetting polymeric material, is widely used in many fields, such as in coating, construction, transportation, electronic and electrical industries (EE) due to its excellent electrical insulation performance, high mechanical strength and good chemical resistance [1][2][3][4][5]. In general, EE products require a flameretardancy grade to guarantee its safety of use in heated environment.…”