Synthesis Of A Curing Agent Containing Phosphorus And Triazine For Intrinsic Flame-retarded Epoxy Resin

Epoxy resin as an important thermosetting polymer materials, with high mechanicalstrenth, high corrosion resistance, high dimensional stability, excellent insulation andadhesion properties, etc., are widely used in adhesives, coatings, aviation and electronicindustries. Generally crued epoxy resins without flame-retardant modification are flammable,and the LOI only reach20%. It is essential to improve its flame retardant in application.Based on the current research trends, the research of highly efficient and environmentalfriendly flame-retardant cured epoxy is necessary. Curing agent containing flame retardantelements or groups is a good way to prepare intrinsic flame-retardant epoxy materials, whichare able to obtain excellent flame-retardant properties as well as matain good thermal stability,and mechanical properties.9,10-dihydro-9-oxa-phosphaphenanthrene-10-oxide (DOPO) and derivatives exhibitehigh thermal stability and high flame retardant efficiency, used as a reactive flame resistantsin many polymer matrix. Triazine derivatives having aromatic ring structure, exhibite highheat resistance, high strength, and good chemical stability, used in many functional materials.A novel flame-retardant anhydride hardener containing DOPO and triazine structure wassynthesized and used for curing epoxy resins to prepare intrinsic flame-retardant cured epoxy.Its impacts on curing mechanism, flame retardant performance, mechanical properties andthermal stability were systematic studied.DOPO, cyanuric chloride, p-hydroxybenzaldehyde and trimellitic anhydridechlorideusing were used to synthesize a phosphorus and triazine containing anhydridehardener (TDA). FTIR,1H-NMR,13C-NMR,31P-NMR and MS were used in characterizationthe structure of the novel compound. Both TDA and MHHPA were used as curing agent forDGEBA E-51, and cured epoxy (P-EPR) with0wt%~2.0wt%phosphorus content wereprepared. The effects of TDA on curing mechanism of anhydride/epoxy system were studiedby non-isothermal DSC. The results showed that TDA exhibite higher curing activity thanMHHPA. With the increased content of TDA in curing system, the activation energy of curingreaction decreased. Autocatalytic mechanism worked in P-EPR curing system, and the curing kinetic equation of the system is as follow.The vertical flame test and the limiting oxygen index (LOI) test were used to characterize the flame retardant performance of P-EPR. The results showed the that with increasing phosphorus content, both flammability rating and LOI were increased. With phosphorus content of1.5wt%, P-EPR-1.5system achieved UL94V-0and LOI reached32.7%. The LOI of P-EPR-2.0system is up to35.4%. The use of TDA hardener can improve the flame retardancy effectively. DMA analysis showed that with increasing phosphorus content the glass transition temperature of P-EPR system increased slightly at first, then decreased. With the increasing content of TDA in P-EPR system,the stiffness increased while strength and toughness reduced. It is also showed that the use of TDA can improve the water absorption resistance of cured epoxy.