Preparation of cycloimidized melamine and application of flame-retardant epoxy resin
Melamine(MEL)has become a hot topic in the field of flame retardants due to its advantages such as high thermal stability,hydrolysis resistance,low migration,high carbonization,and low price.However,the highly chemically stable aromatic structure of the conjugated six membered nitrogen heterocycles result in low reactivity and difficulty in further modification.To further expand application of the melamine system,MEL and 1,2-cyclohexanedioic anhydride(HHPA)were used as raw materials to prepare cycloimidized melamine derivative(RFR)and applied in the field of flame-retardant epoxy resin(EP).By adjusting the reaction molar ratio of raw materials,time,temperature,solvent,and other factors,the process conditions for RFR were optimized.Meanwhile,the structure of RFR was characterized by Fourier transform infrared spectrum(FTIR),nuclear magnetic resonance,and elemental analysis.Subsequently,by mixing cycloimidized melamine derivative with EP and thermal curing with 4,4-diaminodiphe-nylmethane,the flame-retardant EP was fabricated.Finally,comprehensive evaluation of the structure,mechanical properties,resid-ual carbon content,and flame retardancy of flame-retardant EP was conducted by means of limiting oxygen index(LOI),vertical combustion,universal tensile testing machine,FTIR,thermogravimetric analysis and scanning electron microscopy(SEM).The results show that when the mass fraction of RFR is 7.5%,the char-forming rate increase by 20.5%compared to unmodified EP,the LOI of flame-retardant EP reach 26.3%,and the flame retardant grade reach UL 94 V-1 level.From the perspective of flame-retardant mechanism analysis,this flame retardant synergistically exerts both condensed and gas-phase flame retardancy through the triazine skeleton and cycloalkyl side groups.
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