Effect of hydrothermal ageing on bond strength

Changes in the fibre/resin interfacial zone due to hydrothermal ageing can be detected using the TRI microbond technique for measuring interfacial shear strength. The procedure involves exposing fibre/resin microdroplet assemblies to the specified environmental condition for a given time and comparing their interfacial shear strengths with those of unaged specimens. We have investigated the effect of hydrothermal exposure on Kevlar^® 49, AS4 carbon and E-glass fibres embedded in Epon 828 thermosetting resin and two thermoplastic resins (polyethylene and polycarbonate). For the fibres embedded in Epon 828 and polycarbonate resins, consistent and significant bond strength reductions (13–50%) were obtained after refluxing in water at 88°C. These reductions could be partially or completely reversed, depending on the fibre/resin system. In contrast, interfacial shear strengths for the same three fibres embedded in polyethylene resin were increased irreversibly by 36 to 46% upon exposure to water at 88°C for 24 h. Evaluation of these results suggests that the mechanisms of bond strength changes due to hydrothermal ageing may be different for various combinations of fibres and resins.