Synthesis Of Polyphosphazene Hybrid Strontium Hydroxystannate Nanorods And Its Flame Retardancy On Epoxy Resin

Epoxy resins（EP）are widely used in many fields such as insulation coatings,casting materials,electronic industries and so on due to their excellent chemical and corrosion resistance,high adhesion,good electrical insulation performance and dimensional stability.The flammability of EP,however,is a major hazard in their applications,especially in aerospace and military.Therefore,the development of flame retardant of EP has become an important research direction.To date,the commercial flame retardants are difficult to increase the flame retardancy of EP with a small amount of addition（<5%）.The purpose of this paper is to develop a novel hybrid organic-inorganic flame retardant and smoke suppressant by combining the double metal salt with polyphosphazene.In this paper,the nanorods strontium hydroxystannate（SrSn（OH）₆）nanorod was rapidly synthesized by one-step homogeneous precipitation at room temperature by using sodium stannate trihydrate and strontium nitrate as raw materials.And then the synthesized SrSn（OH）₆ was coated with polyphosphazene derivative（PZS）to obtain a core-shell structured organic-inorganic hybrid nano-flame retardants（PZS@SrSn（OH）₆）.The morphology and chemical structure of SrSn（OH）₆ and PZS@SrSn（OH）₆ were characterized by SEM,TEM,CA,XRD and FTIR.The results showed that SrSn（OH）₆ with uniform particle size has been successfully prepared.PZS@SrSn（OH）₆nanorods presents core-shell structure,and also exhibits better hydrophobic properties.The thermal degradation behavior of SrSn（OH）₆ and PZS@SrSn（OH）₆ was investigated by thermogravimetric analysis（TGA）.The results showed that SrSn（OH）₆ nanorods start to loss water at 217°C.The final weight loss was 19.6%.The maximum thermal degradation rate of the first stage of PZS@SrSn（OH）₆ was reduced by about 41.3%compared to that of SrSn（OH）₆.The reduced thermal degradation rate and better char-forming ability of PZS@SrSn（OH）₆ are attributed to the core-shell structures between PZS and SrSn（OH）₆.The synthesized SrSn（OH）₆ and PZS@SrSn（OH）₆ nanorods were applied into EP to prepare SrSn（OH）₆/EP and PZS@SrSn（OH）₆/EP composites.The thermal stability of the EP composites was studied by TGA.The limiting oxygen index（LOI）and cone calorimetry（Cone）were used to investigate the flame retardant properties of EP composites.TG data showed that both SrSn（OH）₆/EP and PZS@SrSn（OH）₆/EP composites showed a one-step degradation process,as same as pure EP.When 3 wt%of SrSn（OH）₆ and PZS@SrSn（OH）₆were added,the char residue at 800°C was increased from 13.1%of pure EP to 16.5%and17.0%,respectively,which was higher than the theoretical value of 15.0%and 14.7%.The addition of SrSn（OH）₆ and PZS@SrSn（OH）₆ nanorods in EP exhibits high flame retardant efficiency and smoke suppression effect,and a significant synergistic effect occurs between PZS and SrSn（OH）₆.When 3 wt%SrSn（OH）₆ and PZS@SrSn（OH）₆ were added into EP,the LOI value was increased to 28.4%and 29.6%from 26.2%,respectively.Cone results showed that the char residue was increased by 237.0%,and the peak heat release rate（PHRR）,total heat release（THR）,total smoke production（TSP）,and carbon monoxide production rate（COP）were reduced by 29.0%,11.1%,22.9%and 38.5%,respectively.To further investigate the flame retardant mechanism,the chars after Cone tests of PZS@SrSn（OH）₆/EP composites were analyzed by XRD,SEM,FTIR and EDS.The results showed that non-flammable gas were generated from PZS@SrSn（OH）₆ at high temperature,which dilutes the concentration of combustible gas.The formation of a dense structural char layer can insulate the decomposition products and the exchanges between heat and oxygen.PZS@SrSn（OH）₆ play a role in both gas phase and condensed phase for the flame retardancy of EP,thereby significantly increasing the flame retardant and smoke suppression of EP.The synthesis of PZS@SrSn（OH）₆ provides theoretical basis for the development and research of novel hybrid organic-inorganic flame retardants.