Moisture absorption in VARTMed three-dimensional braided carbon-epoxy composites with different interface conditions

Epoxy resin-based composites reinforced with three-dimensional braided carbon fabric composites (C3D/EP) were prepared by a vacuum assisted resin transfer molding (VARTM) process. In this study, the moisture absorption behavior of the C3D/EP composites with different interface conditions was investigated. The role of interface condition was evaluated by comparing weight gain, diffusion parameters, and reductions of mechanical properties of the two 3D composites with different interface conditions, as well as by SEM observation. The weight change and diffusion parameters were determined by immersion tests and the mechanical properties degradation was investigated by examining flexural and shear properties during hygrothermal aging. It was found that moisture absorption behavior and losses of mechanical properties were interface dependent. The composites of higher interface strength showed lower moisture absorption rate (k) and diffusion coefficient (D) values at 37 °C and 80 °C, and a lower equilibrium moisture content (M∞) at 37 °C, but a higher M∞ at 80 °C. A mechanism was proposed to elucidate interface dependence of hygrothermal aging. In addition, a comparison to the unidirectional composites was made to assess the influence of fiber structure.