Zinc hydroxystannate coated by polyphosphazene to improve the fire safety and suppress the smoke of epoxy resin

A novel flame retardant containing zinc, tin, phosphorus and nitrogen elements is synthesized from 4,4-Diaminodiphenyl ether (ODA), Phosphonitrilic chloride trimer (HCCP), Triethylamine (TEA) and 1,4-Dioxane by polycondensation reaction. Herein, a hollow, encapsulated material (hollow zinc hydroxystannate@polyphosphazene, H-ZHS@PZS) is introduced as a flame retardant into epoxy resin (EP). And the hollow structure can delay the release of decomposition products and the diffusion of heat. Thermogravimetric analysis (TGA) shows that the EP has good thermal stability after adding H-ZHS@PZS, and the material weight loss of 5 % corresponds to a minimum temperature of 328.4 °C, and the residual carbon mass increases by 77.7 % compared to the pure EP. The well-designed H-ZHS@PZS has good flame retardancy. Cone calorimeter tests (CCT) show that introducing 5 % H-ZHS@PZS into the EP reduces the peak of heat release rate, total heat release, total smoke production, and peak CO production rate by 55.4 %, 19.7 %, 22.5 %, and 59.3 %, respectively. Benefiting from a well-formed nanosheet-polymer interfaces, the mechanical performance is improved. It is worth noting that the improved flame retardancy of EP is mainly assigned to the physical blocking of H-ZHS and the structure of PZS promotes the formation of a dense and continuous char in the condensed phase.