Preparation Of Multifunctional Nitrogen-Containing Flame Retardants And Research Of Its Application In Flame-Retardant Epoxy Resins

In recent years,Epoxy resins(EPs)have been widely used in many fields,it has excellent physical,mechanical,electrical insulation and adhesive properties with various materials.However,traditional EPs have a high fire risk factor and pose a threat to human life and property if it burns,so it is important to enhance their fire-safety properties for other fields,especially civil aviation.In traditional flame retardants,halogen-containing flame retardants have been gradually restricted in recent years due to the release of hydrogen halide gases and poisonous substances during combustion,as well as the residual permanent pollutants that can be harmful to the environment.Phosphorus-containing flame retardants are promising alternatives with higher flame retardancy and lower toxicity,but phosphorus-containing flame retardants are easy to cause secondary pollution and release corrosive acids,which ultimately have a very negative impact in the environment.And their source is generally non-renewable phosphate rock.Based on the above analysis,this thesis proposes to design two kinds of halogen-free and phosphorusfree cross-linked flame retardants based on nitrile-based cross-linking,and add them to EPs to prepare flame-retardancy EP thermosets.And the thermal stability and flame-retardant mechanism are investigated.The main contents of this thesis are as follows:(1)A benzoxazine-containing phthalonitrile flame retardant(BA-Ph)was synthesized from 3-APN,formaldehyde and bisphenol A,the flame-retardant EP thermosets were prepared with the appropriate proportion of curing agent.After testing,it was found that the flame retardancy of the EP thermosets was improved,and the thermosets could pass the UL-94 V-0rate and reach a LOI value at 32.7% at a very low addition amount(10wt%);In terms of thermal stability,the residual char of the EP thermosets at high temperatures was also increased,because of the cured nitrile group and oxazine ring underwent double cross-linking to form a stable triazine ring and hyperbranched structure;Analyzing the gas products of the EP thermosets at different temperatures,it was found that the incombustible gas such as ammonia were produced,that could dilute combustible gas and oxygen.The above experimental results showed that the cross-linked flame retardant could effectively enhance the flame retardancy of the EP thermosets,and the characterization results of the flame-retardant mechanism showed that the flame retardant exhibited excellent flame retardancy in both gas phase and condensed phase.(2)An allyl-containing phthalonitrile flame retardant(DBA-Ph)was synthesized from an allyl bisphenol A and 4-nitrophthalonitrile,and an additive flame-retardant EP thermosets was prepared with an appropriate proportion of curing agent.After testing,it was found that the flame retardancy of the EP thermosets had improved,and it already passed the UL-94 V-0 rate and reached a LOI value at 32.9% at a very low addition amount(10wt%).This indicated that the multiple cross-linking network would endow the EPs with a denser and harder char residue,thus further improving the flame retardancy.