Diffusion Characteristics of Moisture in Polymer Composites under Different Hygrothermal Conditions

The diffusion of moisture in composite materials is a complex phenomenon. In this investigation, effects of temperature, laminate architecture and cyclic hygrothermal conditions on the moisture absorption behavior of carbon/epoxy laminates were explored. Both woven and unidirectional laminates were fabricated from carbon fiber reinforced epoxy prepreg materials (CFRP). Specimens were later immersed in water at different temperatures, including room temperature (RT), 60°C and 80°C, or exposed to cyclic hydrothermal conditions. Within the temperature range studied, the diffusion of moisture inside the CFRP laminates followed the Ficks law. Both the diffusivity and the saturation moisture contents of the conditioned laminates increased with temperature. Furthermore, no weight variation was observed when the specimens were stored in a freezer at-30°C. The architecture of the reinforcement fibers also exhibited significant influence on the diffusion behavior of moisture in the laminates. Under the same temperature, the diffusivity of moisture in woven laminates was higher than that in unidirectional laminates.