Preparation Of DOPO-containing Epoxy Resin Systems And Their Flame Retardancy

Epoxy resin is one of the most widely used thermosetting resins due to its excellent physical and mechanical characteristics,electrical insulation property,chemical resistance,outstanding adhesion performance and dimensional stability.However,flammability is one of the main drawbacks of epoxy resins.Traditional halogen-containing flame retardants are forbidden by the environmental protection laws and regulations in many industrial applications.Therefore,phosphorus-containing flame retardants have attracted a great deal of attention.DOPO is an effective and environmental friendly reactive flame retardant,Due to its biphenyls and phenanthrene ring structure,DOPO is more thermally and chemically stable than normal organic phosphate and become the most widely used flame retardant in epoxy resins.The preparation and the flame retardant mechanism of DOPO-containing epoxy resins are the focus of research in recent years.In this dissertation,DOPO-containing epoxy resins and different type of curing agents were prepared,the flame retardant mechanism of DOPO and the synergistic flame retardant mechanism of phosporus and nitrogen were studied.The main studies are as follows:(1)Phosphorus-containing epoxy resins(DOPO-CNE)were synthesized by DOPO and ocresol formaldehyde epoxy resin(CNE),the catalytic effect of triphenylphosphine on the reaction of DOPO and CNE was studied.The calculated reaction activation energy decreased from 162.2 kJ/mol to 113.8kJ/mol due to the catalytic effect of triphenylphosphine(at 1.5wt% dosage)according to non-isothermal DSC method.The reaction of DOPO and CNE was completed in 2 hours at 130? according to APC test results.(2)Novolac resin was prepared and used as a curing agent for DOPO-CNE.The activation energy of the curing reaction is calculated to be 67.7kJ/mol according to non-isothermal DSC method.The thermal stability,thermal decomposition mechanism and flame retardancy of the phosphorus-containing epoxy resin were studied by simultaneous thermal analysis,LOI and UL 94 vertical test.The results showed that DOPO structure decomposed to phosphoric acid in air atmosphere while decomposed to benzofuran and PO free radical in nitrogen atmosphere,the DOPO-CNE(2%P)/PN cured resin system can achieve V-1 rating(LOI=27%),the DOPO-CNE(3%P)/PN cured resin system can achieve V-0 rating(LOI=31%).(3)Melamine modified resole resin was prepared and used as curing agent for DOPOCNE.The activation energy of the curing reaction is calculated to be 62.6kJ/mol according to non-isothermal DSC method.The thermal stability,flame retardancy,microscopic morphology of chars,phosphorus and nitrogen content were characterized by TG,cone calorimeter,LOI,UL 94 vertical test,SEM,atomic absorption spectrometer and elemental analyzer.The results showed that the flame retardant efficiency of phosphorus element was higher than that of nitrogen element,nitrogen mainly affected the flame in the gas phase while phosphorus mainly affected the flame in the condensed phase,a synergy of the gas phase effect and the condensed phase effect was observed,the epoxy resin with 1.4wt% phosphorus can achieve V-1 rating(LOI=26%),while the epoxy resin with 1.4wt% phosphorus and 4.1wt% nitrogen can achieve V-0 rating(LOI=28%).(4)DOPO-DICY was successfully synthesized by DOPO and DICY under the condition of 200? for 3h.The structure of DOPO-DICY was studied by IR and NMR.The activation energies of the curing reaction of CNE by DICY and that of CNE by DOPO-DICY are 100kJ/mol and 74.5kJ/mol,respectively,according to non-isothermal DSC method.The thermal stability,flame retardancy and microscopic morphology of chars were studied by TG,cone calorimeter,LOI,UL 94 vertical test and SEM.The results showed that the heat release rate of epoxy resin cured by DOPO-DICY decreased,a protective carbonaceous layer was formed on the surface of char after combustion,the CNE cured by DOPO-DICY can achieve V-0 rating and LOI achieve 30%.(5)Phosphorus and nitrogen containing novolac resin(DOPO-DICY-PF)was synthesized by DICY,phenol,formaldehyde and DOPO.The structure of DOPO-DICY-PF was characterized by IR and NMR,the reaction of DOPO and nitrogen-containing novolac can be completed in 2 hours at 120? according to APC test results.The activation energy of the curing reaction of CNE by DOPO-DICY-PF is calculated to be 84.3kJ/mol according to nonisothermal DSC method.The thermal pyrolysis,flame retardancy and microscopic morphology of chars were characterized by simultaneous thermal analysis,cone calorimeter,LOI,UL 94 vertical test and SEM.The results showed that the heat release rate and total heat released decreased with the increase of phosphorus and nitrogen content,DICY structrue mainly affected the flame in the gas phase by releasing ammonia gas while DOPO structrue mainly affected the flame in the condensed phase by releasing phosphoric or polyphosphoric acid,a synergy of the gas phase effect and the condensed phase effect was observed,the epoxy resin cured by DOPODICY-PF can achieve the V-0 rating and LOI=29-32%.