Water uptake in epoxy matrix with voids: Experiments and modeling

The influence of voids on the moisture uptake of epoxy matrix has been studied. Specimens with void contents from 0 to about 50% were prepared. Void geometry and content were analyzed using microscopy and density methods. Void-containing samples were characterized by differential scanning calorimetry and dynamic mechanical analysis which verified consistency of chemistry. The moisture uptake of specimens immersed in distilled water at 40℃ was monitored. The rate of absorption and saturation moisture content increased with increasing void content. Mass balance calculations revealed that only 6–8% of the void volume is occupied by water at saturation. The moisture uptake of void-free and void-containing specimens was non-Fickian. The Langmuir model provided better fits to the experimental results, although the high void content specimens showed substantial deviations from the Langmuir diffusion model. The moisture diffusivity of the void-free and void-containing specimens agreed reasonably with the Maxwell inclusion model.