Design Of Transparent Epoxy Resins With Efficient Halogen-free Flame Retardant

Epoxy resins with high transparency and refractive index are widely used in special adhesives,LED,handicrafts and special modules due to its good abrasion resistance,easy to mold and low cost.However,the limiting oxygen index of the epoxy resin is only 19%,leading to its easy to burn,which greatly limits its applications.However,after adding flame retardant in epoxy resins,the transparency and refractive index of epoxy resins will be reduced or even disappeared.Hence,the study on high transparency and refractive index of epoxy resins become a hotpot of the researchers.In this paper,series of reactive flame retardant curing agents were prepared by modifying aliphatic polyamine polyethyleneimine,successfully introduced P,S and other elements into the three-dimensional cross-linking network of epoxy resins.We also deeply studied the mechanical properties,flame retardancy,transparency,curing and flame retardant mechanism of the the epoxy resins.The completed works in this paper are as follows:1?The transparent flame retardant curing agent DPPEI was successfully prepared by diphenylphosphoryl chloride?DPPC?modifying polyethyleneimine?PEI?.The chemical structure was characterized by ¹H-NMR and ³¹P-NMR.The cured products DPPEI-EP was obtained by epoxy resins and DPPEI via curing reaction.Transparency test shows that:DPPEI-EP has excellent transparency for its transparency is more than 90%in the visible light.The study of transparent mechanism proved that the introduction of flame-retardant elements did not change the amorphous of the epoxy resin.Flame retardant test shows:adding 35wt%DPPEI,the LOI of DPPEI-EP increased from 18%to 29.8%and could pass V-0 rating in the UL-94 test.Cone calorimeter shows that:adding 30wt%DPPEI in epoxy resins,the PHRR and THR of DPPEI?30?-EP were reduced by 63.6%and 69.5%compared with PEI-EP,respectively.The flame retardant mechanism reveals that:the synergistic effect of condensed phase and gas phase leading to good flame retardant of the epoxy resins.The above results show that DPPEI can effectively improve the flame retardancy and the transparency of epoxy resins.2?The transparent flame retardant curing agent PTDP was successfully prepared by diphenylphosphoryl chloride?DPPC?,polyethyleneimine?PEI?and thiourea?TA?.The chemical structure of PTDP was characterized by ¹H-NMR and ³¹P-NMR.The cured products PTDP-EP was obtained by epoxy resins and PTDP via curing reaction.Flame retardant test shows:adding 30wt%DPPEI,the LOI of PTDP-EP increased from 18%to30%and could pass V-0 rating in the UL-94 test.Cone calorimeter shows that:adding 30wt%PTDP in epoxy resins,the PHRR and THR of PTDP?30?-EP were reduced by 41.6%and 62%compared with PEI-EP,respectively.Transparency test shows that:PTDP-EP has excellent transparency for its transparency is more than 90%in the visible light.At the same time,the cured epoxy reins PTDP-EP has excellent refractive index,for its refractive index is as high as 1.58;The above results show that PTDP can effectively improve the flame retardancy,transparency and refractive index of epoxy resin.