Study On Preparation And Performance Of Flame Retardant Epoxy Resin Containing DOPO

Epoxy resin has excellent corrosion resistance,acid and alkali resistance,water resistance and insulation,and is widely used in aerospace,electronic devices and construction industries.However,epoxy resin with limiting oxygen index of 21% is a flammable material and has a fire hazard,which limits the application of epoxy resin and threatens life safety of people.The use of halogen-containing flame retardants can solve the flammability problem of epoxy resins,but in terms of safety,environmental protection and flame retardancy,there is an urgent need to develop green and safe flame retardants to improve the flame retardancy of epoxy resin.In this paper,p-aminobenzoic acid,p-hydroxybenzaldehyde,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)are used as raw materials to synthesize a new type long-chain phosphorus nitrogen flame retardant(PhN-DOPO)through a three-step reaction.In the first step,p-aminobenzoic acid and p-hydroxybenzaldehyde under certain conditions are dehydrated and condensed to form an intermediate.In the second step,the intermediate is heated in an acidic environment to undergo an esterification reaction to form a long-chain matrix;The chain matrix and DOPO undergo an addition reaction under suitable conditions to generate a flame retardant(PhN-DOPO).In this paper,Fourier infrared spectroscopy,hydrogen nuclear magnetic resonance spectroscopy,X-ray diffraction analysis and scanning electron microscopy were used to characterize the molecular structure,microscopic morphology and phase of the intermediate,long-chain matrix and flame retardant(PhN-DOPO).The effect of reaction time on the yield of flame retardants was explored,and the best reaction time was obtained.The best synthesis process is reaction between p-aminobenzoic acid and p-hydroxybenzaldehyde at 60°C for 3 hours to generate intermediates,intermediate reacting for 1.5h at 120 ℃ under acidic conditions to form a long-chain matrix,in the end the long-chain matrix and DOPO react at 60℃ for 4h to form a flame retardant(PhN-DOPO).The flame retardant(PhN-DOPO)is added to the epoxy resin according to 0%,5%,10%,15% of the epoxy resin mass and using curing agent(metaphenylenediamine)with an epoxy equivalent ratio of 1:1 in the preparation of flame-retardant epoxy resin.The flame retardant performance and thermal stability of flame retardant epoxy resin are explored by determining limiting oxygen index,scanning electron micrograph of residual carbon,thermal weight loss and differential scanning calorimeter analysis.The results show that the flame retardant performance of EP(10g)increases from21% to 32.4% compared to epoxy resin,but the breaking strength of the material decreases from 58.36 MPa to 37.03 MPa,and the elongation at break decreases from 3.28 mm to 1.79 mm.The addition of flame retardants causes the epoxy resin to become brittle,decreases its ductility and breaking strength.In this article,the plasticizer is 10%,20%,30%,and 40% of the epoxy resin quality to improve the mechanical properties of composite flame-retardant epoxy resin.The flame retardancy and thermal stability of the flame-retardant epoxy resin is explored by determining of the limiting oxygen index,the scanning electron microscope image of the residual carbon,the thermal weight loss and the differential scanning calorimeter analysis.The results show that the limiting oxygen index of EP(10g+20%)has increased from 32.4% to 36.0%,which is the standard for flame-retardant materials.The breaking strength of the material has increased from 37.03 MPa to 73.12 MPa,and the elongation at break has increased from 1.79 mm to 3.13 mm.At this time,the flame-retardant and mechanical properties of the composite flame-retardant epoxy resin have been greatly improved.Above results show that the plasticizer has effectively improved the flame-retardant and mechanical properties of the epoxy resin.