Preparation Of Phosphazene Derivatives And Their Flame Retardant Application In Epoxy Resin

Epoxy resin is an important thermosetting resin with excellent mechanical properties,chemical resistance,heat resistance and easy processing.It is widely used in adhesives,laminates,electronic packaging and coatings field.However,due to the limitations of poor fire resistance and large amounts of smoke during the combustion of epoxy resins,it has been greatly limited in electrical/electronic equipment.In recent years,traditional halogen-based flame retardants have been gradually replaced by halogen-free flame retardants due to environmental and safety problems.The cyclotriphosphazene derivative is a member of the halogen-free flame retardant.It has the characteristics of halogen-free,high phosphorus-nitrogen content and heat-stable phosphazene ring.It is widely used in flame retardant epoxy resin,polylactic acid and polypropylene.Since the pendant group of hexachlorocyclotriphosphazene contains a special active chlorine atom,it can introduce different functional groups to prepare a plurality of phosphazene derivatives and polyphosphazene derivatives.This paper mainly works as follows:1.A novel hexa-substituted bisphenoxycyclotriphosphazene(HCBP)was prepared from hexachlorocyclotriphosphazene and 4-phenoxyphenol.Then,a bridged product intermediate BPD-BCP was synthesized from hexachlorocyclotriphosphazene and biphenyldiol.A novel bridged trisphosphazene flame retardant BPD-BHP was further prepared by replacing the remaining chlorine atoms of BPD-BCP with phenol.Finally,a polyphosphazene flame retardant poly(HCCP-co-PEI)was prepared by using hexachlorocyclotriphosphazene and polyethyleneimine(PEI)as raw materials.And the flame retardant was structurally characterized by Melting point test,fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance spectrometer(NMR),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and elemental analyzer(EA).2.The HCBP flame retardant is added to the DGEBA/DDM composite system,and cured to obtain a flame retardant epoxy resin.The thermal performance analysis by differential scanning calorimetry(DSC)test shows that as the amount of HCBP added increased,the T_g values of the flame retardant epoxy resin decreased slightly,indicating that HCBP exhibited a mild plasticizing effect.Through the thermogravimetric analysis(TGA)test results,the flame retardant HCBP itself has a high initial decomposition temperature and carbon residue.After compounding with epoxy resin,the carbon residue rate and thermal stability of the epoxy resin are improved.The flame retardant properties are analyzed by the limiting oxygen index LOI,the vertical burning test UL-94 and the cone calorimetry(Cone)test.The results indicated that the addition of 9wt%HCBP oxygen index was as high as33.0%,the burning time was shortened,and UL-94 was close to V-0.The parameters of the flame retardant epoxy resin such as peak heat release rate(PHRR),total heat release(THR),total smoke yield(TSR)and total smoke production(TSP)were greatly reduced.It indicates that the addition of HCBP flame retardant can reduce the effective heat release and smoke yield of epoxy resin.The gas phase products and carbon residue were characterized by Thermogravimetric Infrared(TG-FTIR),Scanning Electron Microscopy(SEM),Energy Dispersive Spectroscopy(EDX)and Raman(Raman).In the gas phase,the HCBP flame retardant can reduce the strength of the gas phase cracking product and form phosphorus-rich protective carbon layer in the solid phase.Thereby effectively preventing the exchange of heat and oxygen inside the matrix and improving the flame retarding efficiency.3.The bridged phenol-based cyclotriphosphazene(BPD-BHP)is added to the DGEBA/DDM composite system.Analysis of its thermal properties,it is known that with the increase of BPD-BHP flame retardant content,the T_g value of flame retardant EP is similar to that of pure epoxy.It is indicated that the addition of BPD-BHP flame retardant does not deteriorate the glass transition temperature of the composite.Thermal stability analysis shows that BPD-BHP itself has high char forming behavior and thermal stability under nitrogen.When added to epoxy resin,the carbon forming ability and thermal stability of the flame retardant epoxy resin are obviously improved.The flame retardancy of the epoxy resin showed that the EP/9wt%BPD-BHP oxygen index was as high as 30.3%and passed the V-1level.Finally,the analysis of its gas phase products and solid carbon residue shows that BPD-BHP flame retardant can act on both the solid phase and the gas phase to reduce the combustion behavior of the epoxy resin.4.The polyphosphazene microsphere poly(HCCP-co-PEI)is added to the DGEBA/DDM composite system,and the modified flame retardant epoxy resin is obtained after curing.By analyzing its thermal performance,it can be known as the content of poly(HCCP-co-PEI)microspheres increases,the glass transition temperature gradually reduces,indicating the addition of nano-type flame retardant has little influence on the structural stability of epoxy resin.Thermal stability analysis indicate that the flame retardant itself has a lower decomposition temperature and a higher amount of carbon residue,and the addition of epoxy resin increases the carbon residue rate to some extent.According to the flame retardant test results,the oxygen index in EP/3wt%FR can only reach 27.0%,without any grade.In order to explore the flame retardant effect of flame retardant,the analysis of flame retardant EP gas phase products and solid phase carbon residue shows that poly(HCCP-co-PEI)microspheres also have the function of catalyzing carbon formation and can effectively reduce combustible gas.The strength reduces the supply of combustible gases.However,the combustion test still needs to be further explored.