Non-linear response of environmentally aged polymer composites: a physicochemical and mechanical study

In this paper, the anomalous behaviour of polymer composites subjected to hygrothermal aging is discussed in reference to the results of a characterization study on polyester matrix fibre reinforced polymer (FRP) composites. Hygrothermal aging, the combination of moisture and elevated temperatures, has been proven to affect the durability of FRPs. Significant structural degradation can be expected as a consequence of hygrothermal aging, however it has been shown that some material properties exhibit a strong non-linear and even beneficial behaviour as a consequence of hygrothermal exposure, indicating the presence of different competing mechanisms. To study these different mechanisms which control the structural performance of an exposed material, FRP samples were exposed to short-term hygrothermal aging for 112 days. Moisture absorption characteristics and mechanical performance were assessed at prescribed time frames throughout aging. With a view to examining any induced intrinsic and surface characteristics, Computed Tomography scan (CT-scan) and Scanning Electron Microscopy (SEM) were also employed. Lastly, impedance spectroscopy was used as an innovative tool to efficiently follow moisture absorption during aging.