Preparation Of Cyclotriphosphazene/DOPO Based Flame Retardant And Its Application In Flame Retardant Epoxy Resins

Epoxy resins are widely used in electronic and electrical appliances,aerospace parts,construction and other industries due to excellent mechanical properties,corrosion resistance,good insulation and other characteristics.However,epoxy resins are potentially dangerous because of its highly flammable property.Therefore,improving the flame retardancy of epoxy resin is of great significance to broaden its application field and protect people’s life and property safety.In this paper,two phosphonitrile macromolecule flame retardants,Hexa-(Nhydroxyethylamino-DOPO-methine-phenoxy)-cyclotriphosphazene(HEACTP-DOPO)and Hexa-(N-hydroxyethylamino-DOPO-methylene-2-methoxy-phenoxy)-cyclotriphosphazene(HVPA-DOPO),were synthesized for the study of epoxy resin flame retardancy,and they were compounded with aluminum diethylphosphinate(ADP)and montmorillonite(MMT)for epoxy resin flame retardancy respectively.Six types of flame retardant epoxy resin curing compounds were produced,and the thermal stability and flame retardant properties of flame retardants and flame retardant epoxy resin curing compounds were tested.The main research contents and conclusions are as follows:(1)HEACTP-DOPO was synthesized from phosphonitrilic chloride trimer(HCCP),phydroxybenzaldehyde,ethanolamine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO),and its molecular structure was characterized by fourier transform infrared spectrometer(FT-IR)and nuclear magnetic resonance(NMR).Preparation of CTP/Ds flame retardant epoxy resin curing compound by using 4,4’-diaminodiphenyl sulfone(DDS)as curing agent.The results of thermogravimetric analysis(TGA)showed that the addition of flame retardant reduced the initial decomposition temperature and maximum thermal decomposition rate of CTP/D-4 and enhanced the amount of residual carbon at high temperatures.CTP/D-4 is UL-94 V-1 rated with a 32.5% limiting oxygen index(LOI).Cone tests showed that compared to epoxy resin(DGEBA),the peak heat release rate(PHRR)and total heat release(THR)of CTP/D-4 decreased by 30% and 37%.A continuous dense carbon layer was observed by scanning electron microscope(SEM).Meanwhile,Raman tests demonstrated that the flame retardant increased the graphitization of the residual carbon.The flame retardant has less effect on the transparency of the material,but the mechanical properties are reduced due to the large molecules and the presence of rigid groups.(2)HEACTP-DOPO was compounded with ADP and MMT to produce CTP-ADP/Ds and CTP-MMT/Ds,two types of flame retardant epoxy resin curing compounds.The TGA results showed that the compound flame retardant reduced the initial decomposition temperature and maximum decomposition rate of the material,and increased the amount of high temperature carbon residue.In the UL-94 test,CTP-ADP/D-3 and CTP-MMT/D-3 passed the V-0 level,and the LOI values reached 37.0% and 32.2%.Cone results showed that compared with DGEBA,PHRR and THR decreased by 40% and 42% for CTP-ADP/D-3 and 59% and 39%for CTP-MMT/D-3.SEM and Raman tests showed the formation of a continuous dense carbon layer with a good degree of graphitization.ADP and MMT are insoluble in epoxy resin,so the transparency and mechanical properties of the material are reduced.(3)HVPA-DOPO was synthesized from HCCP,vanillin,ethanolamine,and DOPO,and its structure was characterized.Preparation of PA/Ds with DDS as curing agent.The heat resistance,flame retardancy and combustion behavior of the material were tested by TGA,LOI,UL-94 and cone.The morphology of the formed carbon layer was observed by SEM,and the graphitization of the residual carbon was tested by Raman Studies have shown that HVPADOPO can slow down the thermal degradation behavior of materials,improve thermal stability,and promote epoxy resin into carbon.PA/D-4 has a LOI of 28.4% with UL-94 V-1 rated.Compared to DGEBA,the PHRR and THR of PA/D-4 decreased by 46% and 47%.Raman testing showed that the graphitization degree of residual carbon increased.A continuous dense carbon layer was observed by SEM,which can play a role in oxygen insulation and heat insulation,thereby improving the flame retardancy of epoxy resin.The flame retardant has less effect on the transparency of the material,but due to the larger molecules,it reduces the crosslink density of the epoxy resin and the presence of rigid groups,resulting in a decrease in mechanical properties.(4)HVPA-DOPO is compounded with ADP and MMT respectively to produce two types of flame retardant epoxy resin cures,PA-ADP/Ds and PA-MMT/Ds.TGA results show that the cured flame retardant epoxy resin degrades and carbonizes in advance,and the initial decomposition temperature is reduced,which improves thermal stability and carbonizing ability.The LOI values of PA-ADP/D-3 and PA-MMT/D-3 were 33.0% and 26.0%.And the UL-94 test passed the V-0 and V-1 levels.Compared to DGEBA,the PHRR of PA-ADP/D-3and PA-MMT/D-3 decreased by 58% and 60%,and the THR decreased by 50% and 36%.SEM and Raman tests showed that the addition of flame retardants promoted the formation of a more continuous and dense carbon layer that could catalyze a highly graphitized phosphoruscontaining cross-linked network carbon layer in the matrix.Because ADP and MMT are insoluble in epoxy resin,so the transparency and mechanical properties of the material have a tendency to decline.