STUDY OF THE INTERFACIAL DEGRADATION OF A GLASS EPOXY COMPOSITE DURING HYGROTHERMAL AGING USING WATER DIFFUSION MEASUREMENTS AND DYNAMIC-MECHANICAL THERMAL-ANALYSIS

The hygrothermal degradation of a glass fiber/epoxy unidirectional com posite is investigated by moisture sorption/desorption experiments and dynamic mechanical thermal analysis (d.m.t.a.). At short immersion ti mes, water sorption in distilled water can be satisfactorily described by using Fick's law. The three-dimensional analysis of water diffusio n in parallelepipedic samples shows that no significant interfacial ca pillary flow occurs during the initial Fickian step where water sorpti on occurs mainly by diffusion through the epoxy network. This conclusi on was found to be valid even at the most elevated ageing temperature (90-degrees-C). Slow positive deviations from the Fickian behaviour ar e noticed for long ageing times at 70 and 90-degrees-C. They have been found to be correlated to some interfacial debonding, as indicated by an enhanced desorption rate during thermogravimetric analysis (t.g.a. ) scans. During these non-Fickian sorption steps, the d.m.t.a. spectra of the aged composite also reveal the progressive appearance of an ir reversible broadening of the damping peak associated with the alpha-re laxation. These processes have been attributed to the occurrence of sp ecific morphological changes and debonding at the interphase during ag eing. It is concluded that the hygrothermal degradation of the interfa ce occurs essentially in the non-Fickian sorption steps when the epoxy matrix is close to saturation.