Diffusion of moisture in adhesive bonds.

Enhanced diffusion through the interface between the adhesive and the adherends may lead to rapid degradation of adhesive joints. Specimens with different types of adherend surfaces were tested and compared with moisture absorption predictions from bulk specimen data. Coated samples, where only one face of the sample was attached to the adherend, behaved the same as bulk specimens. In full joints where only the small area of the edges is available for absorption there was an increased absorption over the predictions. However, some uncertainties about the validity of the models and the input data at low concentrations prevent definitive conclusions from being made. The feasibility of using a low cost dielectric sensor, which can be embedded within polymeric materials, to monitor moisture concentration was investigated. The measured capacitance was sensitive to moisture concentration and reasonable correlations could be made at low moisture concentrations. However, at high moisture concentrations the results were highly scattered suggesting further development of the technique is needed.