Effect of hygrothermal fatigue on dynamic mechanical properties and morphology of neat and glass‐reinforced vinyl ester composites

Abstract A neat vinyl ester and a series of glass‐reinforced vinyl‐ester composites were prepared and investigated. All specimens were exposed to various syclic hygrothermal fatigue treatments, which differed from one another by the temperature and the duration of a cycle. Changes induced by the hygrothermal fatigue were studied by weight‐gain measurements, dynamic‐mechanical analysis, and electron microscopy. The T_g of fatigued composites were found to be determined by the amount of moisture absorbed within the resin network. The overall weight gain, however, also includes the moisture absorbed within the resin‐reinnforcement interphase and is a function of the type of composite, the surface treatment of the reinforcement, and the temperature and duration of the fatigue cycle. A semiquantitative concept of the mechanism of water absorption in themoset‐matrix composites has been advanced on the morphological level in order to interpret the experimental results.