Preparation And Properties Of A Novel Phosphorus-nitrogen Synergistic Flame Retardant Epoxy Resin

Epoxy resin(EP),as a commonly applied thermosetting plastic,has been widely used as a composite matrix,including in aerospace and aircraft manufacturing.However,EP is highly flammable and has serious fire hazard,which threatens the safety of human life and property,and also limits the wide application of EP.Therefore,it is important to modify the EP with flame retardant.9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)is an eco-friendly and efficient phosphorus-containing flame retardant with excellent flame retardant effect on EP.In addition,the structure of DOPO contains active P-H bonds,which can generate derivatives by reaction with other compounds.However,DOPO requires a large amount of addition when used alone to achieve excellent flame retardant effect.Based on the above analysis,two novel DOPO derivatives containing phosphorus and nitrogen were designed from the molecular design perspective based on DOPO.And they were added to EP as flame retardant and 4'4-diaminodiphenyl sulfone as curing agent to prepare flame-retardant epoxy thermosets.The flame retardancy,thermal stability and flame retardant mechanism of flame-retardant epoxy thermosets were investigated through performance characterization.The main contents of this paper are as follows:1.A novel DOPO-copper phthalocyanine(DOPO-Cu Pc)flame retardant was synthesized from DOPO,bisphenol A-type phthalonitrile containing benzoxazine and cuprous chloride.The flame-retardant epoxy thermosets were prepared using DDS as a curing agent.The structures of the flame retardants were characterized by infrared spectroscopy and nuclear magnetic spectroscopy.It was found that DOPO-copper phthalocyanine inhibited the curing reaction of EP,but its processing performance was improved.The thermal stability of the epoxy thermosets decreases,but the char yield at 800? is greatly improved.In terms of flame retardant performance,DOPO-Cu Pc can significantly improve the flame retardancy of EP.When the addition of DOPO-Cu Pc is 15 phr,the flame retardant grade reached UL-94 V-0 level and the LOI reached 35.8%.The flame retardant mechanism of DOPO-copper phthalocyanine includes the bursting effect of phosphorus radicals,the dilution effect and "blowing out effect" in the gas phase,and the barrier effect of stable and swelling char layer formed after combustion in the condensed phase.2.A novel DOPO-phthalonitrile flame retardant(DOPO-BAPh)was synthesized from DOPO and benzoxazine-containing bisphenol A-type phthalonitrile,and a flame retardant epoxy thermoset was prepared with DDS as the curing agent.It was found that DOPO-BAPh could promote the curing reaction of EP.In terms of thermal stability,the lower initial decomposition temperature of DOPO-BAPh reduced the thermal stability of the epoxy thermosets,but enhanced the char yield at high temperature.In terms of flame retardant properties,DOPO-BAPh exhibited high flame retardant efficiency.The addition of 5 phr of DOPO-BAPh enabled the epoxy thermosets to achieve UL-94 V-0 and an LOI of 35.8%.The epoxy thermosets could generate phosphorus-containing radicals to interrupt the combustion chain reaction and dilute the concentration of oxygen and volatile combustible gases when it burns.In addition,the "blowing-out effect" also provided flame retardant effect for EP.DOPOBAPh can promote the cross-linking of EP to form a stable char layer as a protective barrier to protect the bottom epoxy matrix from thermal radiation.During the combustion process,DOPO-BAPh can promote the cross-linking of EP to form a stable carbon layer as a protective barrier to protect the bottom epoxy matrix from thermal radiation.