Synthesis of functionalized Salen‐Ni‐based polyphosphazene flame retardant and its performance study

Abstract A novel functional copulatory polyphosphazene microsphere (Salen‐PZN‐Ni‐KH550) was successfully synthesized via reaction of the surface of Salen‐Ni‐based polyphosphazene (Salen‐PZN‐Ni) with 3‐aminopropyltriethoxysilane, and it was introduced as an additive flame retardant in pure epoxy resin (EP). Thereafter, the effects of the prepared flame‐retardant Salen‐PZN‐Ni‐KH550 on thermal stability, combustion performance, and flame‐retardant mechanism of the EP system were studied in detail. The addition of Salen‐PZN‐Ni‐KH550 led to a significant increase in thermal stability and formation of carbon residue in the EP at a temperature of 800°C. The results showed that the addition of 5 wt% Salen‐PZN‐Ni‐KH550 lowered the maximum heat release rate, as well as the peak smoke release rate by 28.83% and 25.71%, respectively. This resulted in a significant improvement in the fire safety of EP. Additionally, the introduction of Salen‐PZN‐Ni‐KH550 considerably inhibited the evolution of the toxic gas CO and of other volatile products that are produced during the decomposition process of EP. The results of study suggest that mechanism of the flame retardant may be associated to gas‐phase quenching, incombustible gas release, synergistic catalytic carbonization effect and to the formation of components with extremely high thermal stability. The fire safety of EP composites and the reduction of toxic gases can be attributed to the synergistic effects of nickel, APTES, and polyphosphazene microspheres. The development of the new flame‐retardant Salen‐PZN‐Ni‐KH550 is an effective strategy to improve the fire resistance of polymers.