Construction of polyphosphazene-functionalized Ti3C2TX with high efficient flame retardancy for epoxy and its synergetic mechanisms

As a promising flame retardant, Titanium carbide (Ti3C2TX) MXene has shown synergetic flame retardancy with various modifying agents, especially phosphorus/nitrogen-containing flame retardants. However, the synergetic flame-retardancy mechanism of Ti3C2TX and modifying agent are unclear due to the complexity of reactions during the combustion process. Herein, polyphosphazene-functionalized Ti3C2TX nanosheets (MXene-PZN) were prepared and then added to epoxy resin (EP) to prepare the EP/MXene-PZN composites. Subsequently, the mechanical properties and the flame-retardant performance and mechanism were systematically investigated. The results showed an improved interfacial interaction and excellent compatibility of MXene-PZN nanosheets in the EP matrix, resulting in the storage modulus and tensile strength of EP/MXene-PZN-2.0 being increased by 46.5% and 68.4% respectively, as 2 wt% MXene-PZN was added into the EP matrix. Moreover, the flame-retardant tests showed that the peak heat release rate and total heat release of EP/MXene-PZN-2.0 were reduced by 44.8% and 54.8%, respectively, compared with pure EP, while 49.4% and 41.9% decrease in the peak CO production rate and the peak CO2 production rate were also achieved. Finally, focusing on the main existing forms of MXene-PZN in the EP matrix during different combustion stages, the flame-retardant mechanism of MXene-PZN functioned both in the condensed phase and gaseous phase was established. Thus, this work demonstrates a facile yet promising strategy to design efficient synergetic flame retardants.