Abstract: In this study, the epoxy vinyl ester resin and its glass fiber reinforced composite materials have been successfully prepared, and the mineralized water aging test under high temperature and high pressure (70 ℃+5 MPa) has been conducted to investigate the performance of the degradation as well as the aging mechanism under high temperature and high pressure conditions. It has been found that the mechanical properties of as-prepared resin and composite materials are greatly influenced due to the aging. For instance, after 49 days of aging, the stretching of the composite material dropped to 56.79%. Meanwhile, the residual tensile strength of epoxy vinyl ester was only 27.30%. The characteristic functional groups of the ester within the resin significantly changed during the aging, due to hydrolysis of the ester groups as well as the formation of hydrogen bonds leading to the reduction of the mechanical properties of the materials. According to FTIR and XPS results, the degree of aging gradually decreased from the surface into the interior of the materials. From SEM, it was shown that the fracture failure mode of epoxy vinyl ester gradually changed from ductile fracture to brittle fracture as the aging was processed. In addition, the interfacial debonding occurred within the composite material matrix. In the end, the DMA results indicated that the rupture of the resin molecular chain after aging, as well as the plasticizing effect of water molecules, led to the decreasing of the glass transition temperature and the storage modulus of the composite materials.

Key words: epoxy vinyl resin, composite, aging, strength, micro morphology