| Epoxy resin,as an important thermosetting plastic,has been widely used in various industrial fields because of its excellent properties.However,the limiting oxygen index(LOI)of epoxy resin is only 19.8%,which makes it unable to meet the requirements of many applications and even brings potential dangers.Therefore,improving the flame retardancy of epoxy resin is an urgent problem to be solved.With the enhancement of national awareness of environmental protection,and more relevant laws and regulations on banning halogen flame retardants have been promulgated and implemented one after another,so the development of new halogen-free flame retardants has become a new research focus,especially phosphorus flame retardants.Phosphorus flame retardants have the advantages of high carbonization rate,low toxicity and less smoke.Generally speaking,it is necessary to add at least 1wt% phosphorus to the epoxy resin system in order to make the flame retardant performance of the epoxy resin system more satisfactory.Compared with the addition of single flame-retardant elements,flame retardants containing phosphorus and nitrogen usually have synergistic effect on flame retardancy of polymer materials.In addition,the incorporation of benzene ring or heterocyclic ring can also improve the flame retardant efficiency.In this paper,a new flame retardant curing agent,N,N'-bis(3-triazole)phenylphosphonamide(PPDTA),was synthesized from molecular design,and PPDTA and 4,4'-diaminodiphenylmethane were used for curing epoxy resin.The curing kinetics in the curing process was studied,and the properties of the cured compounds were analyzed.The main contents of the study include the following:(1)Using 3-amino-1,2,4-triazole(TA),phenyl phosphonyl dichlorochloride(PPD)as raw material and tetrahydrofuran as solvent,the product PPDTA,was synthesized by infrared spectroscopy,nuclear magnetic resonance analysis and thermogravimetric analysis.The optimum synthesis process of PPDTA was obtained by 3 × 3 orthogonal experiment,that is,the reaction temperature was 70 ?,the reaction time was 10 h,the feed ratio was n(TA): n(PPD)= 2.2 : 1,and the highest yield was 86.4%.(2)The curing kinetics of PPDTA/DDM-EP system was studied by non-Isothermal DSC.Different DSC curves were obtained by scanning the samples at different heating rates.The theoretical curing characteristic temperature of PPDTA/DDM-EP system is calculated.The initial curing temperature T0 is 75.5 ?,the theoretical curing temperature TP is 121.5 ? and the post-curing temperature Tf is 141.5 ?.(3)The non-isothermal DSC curves were analyzed by Kissinger method,Crane method and Flynn-Wall-Ozawa method,and the apparent activation energy(Ea),per-exponential factor(A)and reaction order(n)of epoxy resin during curing were calculated.The auto-catalysis model and n-order kinetic model were used to analyze and fit the PPDTA/ epoxy resin system.(4)Halogen-free flame retardant epoxy resin was obtained by using PPDTA as curing agent and DDM as co-curing agent.The flame retardancy of the curing system was tested by limiting oxygen index(LOI),)vertical combustion test(UL-94),and the thermal decomposition process of cured compounds was analyzed by thermogravimetric analysis(TG).The glass transition temperature(Tg)of the cured system was measured by dynamic thermodynamic analysis(DMA).The mechanical properties of the cured system were characterized by tensile,bending and impact tests.The results showed that compared with DDM-EP epoxy resin system,the flame retardancy of epoxy resin system could be improved obviously with the addition of PPDTA.When the phosphorus content in epoxy resin system reached 2%,the flame retardancy of epoxy resin system reached the level of V-0 by UL-94 tested.The LOI value was 30.1%,and the residual carbon percentage at 800 ? increased from 14.76% to 23.42%. |
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