Characterization and modeling of the polymerization-dependent moisture absorption behavior of an epoxy-carbon fiber-reinforced composite material

The creation of defects (internal porosity) inside epoxy-based carbon fiber-reinforced composites during the curing process is well known to have a harmful impact on most of the mechanical properties of those materials. One of the main sources of void creation is the moisture absorption of the composite plies during the manufacturing process steps before the composite part cure. In order to get a better control of manufacturing, the moisture absorption behavior of a carbon-epoxy prepreg, which is submitted to a wet environment, is investigated. Moreover, the impact of the resin polymerization state on the water absorption behaviors of the plies will be highlighted. The moisture content is therefore measured as a function of time, temperature and relative humidity for uncured and for different partially polymerized materials. An original model was established in order to predict the moisture content in function of time, temperature, relative humidity and polymerization degree. As a major conclusion, it is demonstrated that the water coefficient of diffusion decreases when the polymerization degree increases.