Preparation Of DOPO Based Halogen-free Flame Retardant And Its Application In Epoxy Resin

Epoxy resin has many excellent properties,such as chemical stability,dielectric properties,mechanical properties,bonding properties,and it has the advantages of low shrinkage rate,easy processing,low price in the production and preparation process.It is widely used in automotive manufacturing,circuit board production,building materials,aerospace and other fields.As a kind of polymer,epoxy resin is extremely flammable,which is accompanied by with drops and a large amount of smoke when burning,and its limiting oxygen index(LOI)is only about 20 %.The biggest obstacle to the further application of epoxy resin is its flammable property,so it is of great theoretical and practical significance to modify epoxy resin with flame retardancy.According to the research concept of high efficiency,low smoke and non-toxic,a large number of flame retardant elements were screened,the structure of flame retardant was designed,and the processing technology was explored.Several flame retardants were synthesized and applied in epoxy resin,and excellent flame retardant properties were obtained.The main research results include:1.The organophosphorus flame retardant DDPPM containing bisphenol A-like structure is designed,and its performance is characterized by substitution reaction and aminomethylation reaction.The organophosphorus flame retardant DDPPM was successfully synthesized through substitution reaction and aminomethylation reaction,and its structure was characterized by Fourier infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(NMR).Flame-retardant epoxy resins with additions of 1 wt%,2 wt%,and 3 wt% were prepared using DDPPM.After testing,when the additive amount is 2 wt%,the epoxy resin cured EP/DDPPM-2 can pass the V-0 level of the vertical combustion test standard(UL-94).The DDPPM/EP spline has been tested,and its maximum increase in impact performance is 21.5 % of the EP/DDPPM-1 sample.Only when the addition amount is 3 wt%,the bending strength decreases(decreased by 0.6 %).Pass a series of tests-including thermogravimetric analysis(TGA),cone calorimetry test(CC),scanning electron microscope test(SEM),energy dispersive spectrum test(EDS),thermogravimetric-infrared combined test(TG)-FTIR),thermal pyrolysis gas chromatography/mass spectrometry(Py-GC / MS)to characterize the combustion behavior of composite materials.The study found that when the addition amount of DDPPM was 3 wt%,the peak heat release rate(PHRR)of the composite material decreased by 17.4 %,and the total smoke release(TSP)decreased by 13.6 %.Both TGA and CC tests found the initial decomposition temperature of the composite material in advance.DDPPM exhibits both gas phase and condensed phase flame retardant effects.2.In order to further improve the mechanical properties of the composite material,the Si-containing flexible segment was introduced on the basis of DDPPM,and the reactive silicon-containing organophosphorus flame retardant DP-PPD was successfully synthesized,and the characterization and performance testing were carried out.The organophosphorus flame retardant DP-PPD was successfully synthesized through substitution reaction and aminomethylation reaction,and its structure was analyzed by Fourier infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(NMR)characterization.Epoxy resin cured products with DP-PPD additions of 2 wt%,3 wt%,6 wt%,and 9 wt% were prepared.After testing,3%DPPPD/EP can pass UL-94 In the V-0 level test,the LOI increased to 30.1 %.The research results of mechanical properties show that adding 6 wt% of DP-PPD,the impact strength of the composite material is increased to 220 % of that of unmodified EP,and the scaly,inverted shape is found when the section is scanned by SEM.The hookshaped irregular structure,which consumes and disperses the impact force,helps to improve the impact performance.In the related characterization tests of combustion behavior(including TGA,CC,SEM,EDS,TG-FTIR,Py-GC/MS),the addition of Si element did not fundamentally change the flame retardant mechanism.Similar to DDPPM system,both have gas phase and condensed phase flame retardant effects.TGA and CC tests show that the addition of PD-PPD advances the initial decomposition temperature of the cured epoxy resin,but both HRR and TSP are inhibited and reduced by 26.7 % and respectively.19.4 %.In addition,the SEM and digital photos of the carbon residue can clearly show that the flexibility of the carbon residue is improved and more complete under the doping of Si element.