Preparation Of Two Silicon-based Flame Retardants And Their Application In Epoxy Resins

It is well known that,epoxy resin（EP）is widely used in coatings,adhesives,electronic devices,aerospace and other fields because of its excellent properties.However,as a polymer,EP is flammable and emits a lot of heat and toxic fumes when burning,which poses a serious fire hazard.Therefore,improving the flame retardant properties of EP is a very important research topic.In recent years,green halogen-free and multi-element flame retardant has become an important trend in the development of flame retardants.Flame retardants containing silicon,phosphorus,and nitrogen have significant effects in improving EP flame retardant performance.This paper studies the optimization of flame retardant preparation conditions and the flame retardant performance in EP aiming at the key problem of low flame retardant efficiency of inorganic silicon flame retardants,in which two composite flame retardants with core-shell structure are prepared by a simple and controllable in-situ polymerization method:ammonium polyphosphate（APP）coated Kaolin and melamine-formaldehyde resin（MF）coated silica（SiO₂）.The study mainly involves the followings:（1）APP-Kaolin flame retardant was prepared with kaolin,phosphoric acid and urea as raw materials.The microstructure of the flame retardant was investigated by Fourier infrared spectroscopy（FT-IR）,X-ray powder diffraction（XRD）and scanning electron microscope（SEM）The effects of raw material ratio and curing temperature on the microstructure and yield of the flame retardant were studied.The flame retardant with high yield and higher decomposition temperature was obtained by adjusting the preparation conditions.The flame retardant particles prepared under the best conditions have an average particle size of 16.58μm,good dispersibility,and a decomposition temperature of 60.9℃higher than that of the ordinary nitrogen-phosphorus flame retardant.The thermal stability and flame retardant properties of EP/APP-kaolin composites were studied by thermogravimetric analyzer（TGA）,microcalorimeter（MCC）and limiting oxygen index（LOI）.The flame retardant efficiency of the flame retardant is significantly higher than that of the single component,and the EP/APP-kaolin shows good char formation and flame retardant properties.Adding 10wt%flame retardant can effectively delay the thermal degradation of EP and increase its high-temperature residual carbon content.Compared with pure EP,when the amount of flame retardant added is 25wt%,the peak heat release rate（pHRR）of EP/APP-kaolin decreased by 45.7%and the LOI increased by 36.0%.The improvement in flame retardant performance is mainly due to the synergistic flame retardant effect of APP and kaolin in the condensed phase.（2）MF-SiO₂ flame retardant was prepared with nano-SiO₂,melamine and formaldehyde as raw materials.The effects of raw material ratio and emulsifier concentration on the microstructure of flame retardant were studied by SEM.Too high or too low raw material ratio or emulsifier concentration will cause a poor coating effect.FT-IR,XRD and transmission electron microscopy（TEM）analysis showed that the flame retardants prepared under the best conditions were cage-like multi-core particles formed by MF coating SiO₂.The flame retardant particle has an average particle size of 8.49μm,high content of N and Si,and high-temperature resistance significantly better than that of pure MF.The thermal stability and flame retardant properties of EP/MF-SiO₂ composites were studied through TGA,LOI,MCC,horizontal and vertical combustion（UL-94）,etc.The overall thermal stability and flame retardant properties of EP/MF-SiO₂ are greatly improved compared with EP.Compared with pure EP,when the amount of flame retardant added is 30wt%,the pHRR of EP/MF-SiO₂ decreases by 36.7%,the LOI reaches 26.0%,and can pass UL-94 HB level.MF-SiO₂ mainly functions through the MF gas-phase flame retardant and SiO₂ condensed phase flame retardant.The combined use of MF-SiO₂and APP can improve the flame retardant performance of EP and reduce the amount of MF-SiO₂ added.When the amount of both is 10wt%,the actual flame retardant performance of the composite material is the best.