Study On Preparation And Properties Of Benzoxazine/Epoxy/DDM Ternary Systems

Benzoxazine is a new kind of thermosetting resin with six-membered heterocyclic structure, usually synthesized from phenols, amines and aldehydes, three parts. It can be ring-opening on the condition of heating with or without catalyst to form a cross-linked network structure. Benzoxazine has some advantageous features, such as high heat resistance, lower curing shrinkage, however, the brittleness, and the curing temperature above220℃has limited the applications.In this paper, Fourier Transform Infrared Spectrocopy (FTIR) and Non-isothermal Differential Scanning Calorimetry method (Non-isothermal DSC) are used to study curing kinetics of benzoxazine/epoxy/4,4’diaminodi-phenyl methane (DDM) resin system. Using Kissinger method and Ozawa method to calculate the apparent activation energy (Ea), average value is120.66kJ/mol; Flynn-Wall-Ozawa method are used to show the relationship between the degree of reaction and Ea. It is found that the apparent activation energy increases with the increased degree of reaction, shows an upward trend, and this trend is gradually slower. After the reaction is judged by Friedman method, it shows obvious consistency with n-th order reaction, experimental results show that the curing reaction of the first half data fits the curve well, due to the diffusion control, the latter half of the data deviates significantly. While, n-th order value by Crane method does not accurately conform the curing reaction process.On the basis of the system kinetic analysis, the curing process are determined,140℃/4h,210℃/4h. Epoxy content and DDM content are investigated, and the composites are prepared next. The experimental results show that with the epoxy resin content increase, the decrease in viscosity of resin system, BED-732shows the best impact strength, is7.3kJ/m2, indicating a certain degree of toughening effect, glass fibers and carbon fibers are used to reinforce the matrix, the impact strength improved more significantly, they are28.6kJ/m2and32.7kJ/m2respectively, shows an outstanding properties. BED-552has the best bending performance, the bending strength is102.6MPa, glass fiber and carbon fiber reinforced composites are206.8MPa and485.0MPa; On the other hand, The addition of DDM also affect the performance, with DDM content increase, gel time and the curing temperature are lower, demonstrating that DDM has catalytic ability. We also studies the heat resistance of the benzoxazine/epoxy/DDM system, experimental results show that the ternary material initial decomposition temperature and peak decomposition temperature are not decrease, but increase,from326.7o℃、381.8℃to346.8℃、391.9℃.800℃char yield decrease, showing a good heat resistance. In summary, the introduction of epoxy into benzoxazine does not reduce the heat resistance, but improves the toughness, and the DDM plays a catalytic role, and improves the preparation process of the resin materials.