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.
Highlights
Epoxy resin (EP) has been widely used as an advanced thermosetting polymer with excellent mechanical properties, electrical insulation properties, adhesive properties, and flexibility in the manufacturing industry’s use process [1,2,3,4,5]
Polyphosphazene is a multifunctional organic–inorganic hybrid material composed of alternating phosphazene units (-P=N-), and its active side groups contribute to the diversity and flexibility of phosphazene materials [18,19,20]
We can find out that the increase of PZS@zeolite-like metal–organic frameworks (ZIFs)-67 content in epoxy composites from 0% to 5%, this LOI value gradually increases from 25.5% to 31.9%
Summary
Epoxy resin (EP) has been widely used as an advanced thermosetting polymer with excellent mechanical properties, electrical insulation properties, adhesive properties, and flexibility in the manufacturing industry’s use process [1,2,3,4,5]. [21,22,23] During this decade, a series of polyphosphazene derivatives have been reported and employed as crosslinking agents, reinforcing agents, and flame-retardant additives to optimize composites’ overall performance. Zhu assembled poly (cyclotriphosphazene-co-4,4 sulfonyl diphonel) nanotubes onto a carbon fiber surface by in situ template polymerization as a new type of multi-scale hybrid reinforcement material. This modification enhanced the flame retardants of epoxy composites and even ameliorated their mechanical properties [25]. Designed composites presented perfect catalytic activity and reusability [26] Multiple functionalizations such as special structure composition and heteroatoms doping can endow these materials with surface modifiability, chemical stability, electrical conductivity, catalytic performance, etc
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