The effects of moisture content in a B-staged, aluminum-filled epoxy film adhesive on the final shear and peel strengths of the fully cured system were studied. Mechanical test results, as well as electron microscopy and infra-red spectroscopy of the fracture surfaces, have indicated that pre-drying of unpacked adhesive for 3.5 hours, which has been stored at low temperature (—18°C), is very effective in upgrading mechanical properties, especially peel strength. Moisturizing pre-dried samples, at increasing levels, resulted in degradation of properties. However, a subsequent drying treatment of the uncured adhesive was demonstrated to enhance recovery of properties, provided the moisture level did not exceed 0, 3% (of the total material). The adverse consequences of high moisture pick-up were manifested in matrix porosity and debonding of the aluminum filler and nylon carrier from the epoxy matrix. Dehumidifying from moisture levels above 0.3% had the same consequences. FTIR (Fourier Transform I. R.) absorption peaks corresponding to water, hydrogen bonding and Dicy (dicyandiamide), have been correlated with the moisture level in the pre-cured adhesive. The possible chemical hydrolysis of Dicy was identified as one of the main mechanisms contributing to degradation of mechanical properties. The effects of moisture pick-up were first characterized with respect to the optimal drying time of the B-staged, filled epoxy adhesive. Pre-drying was followed by remoisturizing to various levels and subsequent dehumidifying (re-drying), with the objective of investigating the effect of reversible and irreversible changes on the cured adhesive shear and peel properties.
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Dodiuk et al. (1988) studied this question.
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