Effects of Coatings on Moisture Absorption in Composite Materials

Report No. ARL-TR-2099
Authors: Newill, James R.; McKnight, Steven H.; Hoppel, Christopher P.; Cooper, Gene R.
Date/Pages: October 1999; 47 pages
Abstract: Polymeric coatings can he used to slow the ingress of moisture in composite materials. The effectiveness of these coatings is limited by the quality and thickness, as well as the moisture diffusivity and solubility. The present study investigates the long-term effectiveness of coatings for thick composite laminates, as well as traditional thin laminates. The results are compared for static and fluctuating boundary conditions, with comparisons showing how theoretical predictions can be used to define the coating performance characteristics for protecting composite structures. The theoretical approach is used to determine important attributes for moisture protection of polymer-matrix composite structures provided by polymeric coatings. Developed solutions are used to evaluate a range of coating materials and thicknesses for thin and thick substrates. The diffusion constants and the saturation levels for the coating material were obtained from the range of available coating materials. The results include typical diffusion patterns for coating materials, saturation of the coating layer, development of moisture through time, and effects of the material properties for the various substrate thickness. Moisture diffusion behavior at the substrate-coating interface is also presented. For relatively thick coating layers, the results show that the diffusion constant and the saturation level of the coating must both be low to significantly affect the diffusion process.
Distribution: Approved for public release
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Last Update / Reviewed: October 1, 1999