Abstract: The development of composite industry requires special resin matrixes with good processing characteristic and high wet-heat resistance for RTM technology. In this paper, three kinds of epoxy resins with high heat resistance, E6110, AFG90 and AG80, were used to modify a diamine-type benzoxazine resin (DC-BOZ). The viscosity characteristics, gelation reaction, curing behavior, polymerization reaction, heat resistance, wet-heat resistance and thermal stability of the mixtures were compared. The results showed that the addition of epoxy resins reduced the viscosity of benzoxazine and extended the pot life. Among them, the viscosity of DC/E6110 was only 333 mPa·s after 10 h at 100 ℃, which meets the requirement of RTM process. The addition of epoxy resins affected the gelation time of the system and increased the curing peak temperature slightly. Epoxy resins can copolymerize with benzoxazine and increase the crosslinking densities of copolymerization systems, resulting in the significantly improvement of heat resistance, wet-heat resistance and thermal stability of the modified resin systems. Particularly, the glass transition temperature (T_g) of cured DC/E6110 was increased to 209 ℃ with an increase of 44 ℃ compared with the polybenzoxazine. In addition, the wet T_gs of all systems decreased, but the wet T_g of DC/E6110 still reached 189 ℃. A new resin matrix with low viscosity and good wet-heat resistance developed in this paper can be used to prepare large composite parts by RTM process.

Key words: benzoxazine, epoxy resin, RTM, low viscosity, wet T_g, composites