Abstract
This research aims to define the characteristics of the mixture of benzoxazine/epoxy copolymer matrix and a reinforced nano-material –graphene. By polymerizing with epoxy and due to its self-construction structure, benzoxazine outstandingly upgrades the matrix mechanical properties and weathering resistance. Meanwhile, graphene notably intensifies the fiber-matrix interface, improving both interlaminar mechanical strength and dynamic fatigue life. The investigation includes: (1) Different oxygen-level functional group graphene concentration, (2) Benzoxazine filler content in epoxy matrix, (3) Oxygen-rich functional group graphene concentration in benzoxazine/epoxy/carbon fiber reinforced polymer (CFRP) mechanical properties, and (4) Hygrothermal aging effects. The research results indicate that oxygen-rich functional group graphene (RF-G) shows better material properties and dispersion than oxygen-depleted functional group graphene (DF-G). Compared to epoxy, 0.5wt% RF-G/EP nanocomposites demonstrates 19.16% and 13.13% enhancement in tensile strength and flexural strength, respectively. The matrix experimental results specify that the value of mechanical strength is proportional to benzoxazine filler content. In this study, 30wt% benzoxazine/epoxy significantly reinforces the mechanical strength: 43.67% increase in tensile strength; 44% in flexural strength. However, benzoxazine/epoxy becomes more brittle with the addition of benzoxazine. Therefore, the impact resistance strength reduces about 70%. In thermal properties, the glass transition temperature (Tg) elevates to 106.72℃(13.36% increase). Additionally, the maximum thermal decomposition temperature (Tdmax) enhances from 334.86℃ to 352.7℃ and the thermal decomposition rate decelerates by 37.39%. The results support that graphene actually intensifies the interface properties, especially for interlaminar shear strength (22.82% increment) and fracture toughness (GIC(ini) increases 112.93%, GIC(prop) 135.21%). The tension-tension dynamic fatigue test confirms that fatigue life is remarkably improved more than twice with the addition of graphene. In hygrothermal aging environment condition test result, 30wt% benzoxazine/epoxy substantially slows down by 51.84% of the water absorption rate. Moreover, the 85℃/85%RH condition causes the worst impact to CFRP composites compared with 25℃/65%RH, 25℃/85%RH, and 85℃/65%RH conditions. The humidity level is the critical dominant factor and high temperature further accelerates the material damage situation.