Preparation And Properties Of Halogen-free Flame Retardant Epoxy Resin Composites

Epoxy resin(EP)is widely used in the fields of electronic and electrical,industrial engineering plastics and aerospace due to its excellent corrosion resistance,insulation and chemical stability.However,epoxy resins are prone to generate flammable small molecules such as hydroxyl groups,carbonyl groups and olefins during pyrolysis,so they have flammable characteristics.In order to improve the flame retardant effect of epoxy resins,the traditional method is to introduce flame retardant such as halogen or inorganic hydroxide.However,halogen flame retardant easily generate more smoke and corrosive gases during the combustion process.Although the inorganic hydroxide flame retardant is non-toxic and suppresses smoke,it has the disadvantages of large filling amount and obvious influence on the mechanical properties of the substrate.Phosphorus-containing compound flame retardant have the advantages of low toxicity and non-corrosive gases,but single phosphorus-based flame retardant have the disadvantages of high smoke and large additions,and because the phosphorus-containing compounds have a typical plasticizing effect on epoxy resins,It will have a significant effect on the thermomechanical properties,mechanical properties and thermal stability of the epoxy resin.Therefore,in order to solve this problem,this paper proposes to prepare a series of synergistic flame retardant with a variety of flame retardant elements to cooperate with different synthetic methods to achieve low smoke,high efficiency flame retardancy and low toxicity of epoxy resin.The main research results of this paper are as follows:1.Designed and synthesized a kind of oligomeric organosilicon phosphate salt(DPK).The synthesis method is simple and the yield is high.It is add to the epoxy resin matrix as an additive flame retardant.Through research,it is find that the glass transition temperature and storage modulus of DPK-EP epoxy resin composites are maintaine.The thermal stability of DPK-EP composites is slightly lower than that of unmodified epoxy resins.The 10% DPK-EP epoxy resin composite has reached the V-0 level(3.2 mm)of the vertical combustion test(UL-94),and the limiting oxygen index(LOI)have been increase from 21% to 31% of pure EP.Through the cone calorimetry test,it was found that the peak heat release rate(PHRR)and total heat release amount(THR)of DPK-EP epoxy resin composite materials were significantly reduced,the smoke release was gradually reduced,and the residual carbon was also significantly improved.2.In order to achieve the purpose of low addition and high efficiency flame retardant,the design and synthesis of oligomeric silicone oxyphosphate flame retardant(DPAK),the synthesis method is simple,the yield is as high as 90%,it is add as a flame retardant additive to epoxy Resin matrix.After research,the DPKA-EP composite material has a slightly improved thermomechanical stability compared to unmodified epoxy resin.The epoxy resin modified by DPAK is basical stable in thermal stability.When the amount of DPAK accounted for 4% of the total mass,UL-94 reached the V-0 level(3.2 mm),and the LOI is increase to 29.5%.The PHRR and THR of DPAK-EP composites were significantly reduced,but the smoke was released The amount is slightly increased at 2.5% DPAK-EP,but the amount of residual carbon has a certain increase,and through the analysis of thermogravimetric infrared(TG-FTIR)and X-ray photoelectron spectroscopy(XPS),DPAK exerts excellent Gas-phase flame retardant and condensed-state flame retardant effect.3.In order to achieve less smoke when the epoxy resin burns,a kind of adjacent benzene ring oligomeric organosilicon phosphate flame retardant(DPHK)is designe and synthesize.Its synthesis method is simple and the yield reaches about 90%.It have been find through research that the dynamic thermomechanical properties of DPHK-EP composites remain stable compared to unmodified epoxy resins.The thermal stability of the flame retardant epoxy resin modified by DPHK is slightly reduce.When the amount of DPHK added is 3 wt% of the total mass of the epoxy resin composite,the UL-94 V-0 level(3.2 mm)is reached,and the LOI is increased to 29%.The PHHR and THR of DPHK-EP composites are significantly reduce,and the smoke emission have been significantly improved,and through TG-FTIR,SEM and XPS analysis,DPHK can give flame retardant epoxy resin composites excellent gas-phase flame retardant and cohesion State flame retardant effect.