Thermo-hydrolytic resistance of polyepoxide–glass fibres interfaces by the microbond test

The use of the microbond test as a tool for the characterization of the thermo-hydrolytic resistance of interfacial zones is critically discussed for polyepoxide based composites materials. It is shown that the differences of properties observed between macroscopic and microscopic scales can induce a difference in aging conditions. The energy release rate vs. time of exposure at 60 °C and 98% RH is reported for epoxyde–amine and epoxyde–anhydride/glass fiber systems. The evolution of the energy release rate is interpreted in terms of different degradation mechanisms: release of internal stresses and plasticization for the short term behavior of both systems, while interfacial hydrolysis is advanced for the long term behavior of the epoxyde–anhydride/glass fiber system. This latter chemical degradation is attributed to the presence of hydrolysis sensitive functional groups in the interphase resulting from the reaction between the anhydride co-monomer and the organosilane coupling agent. Trends for the design of thermo-hydrolytic resistant interphase are given on this basis.