Hydrothermal Aging and Humidity Exposure of Carbon and Basalt Fibers and Life Time Prediction

Fibers as a reinforcement in polymer-based composite materials play an essential role in the composites’ mechanical performance. It is, therefore, crucial to understand how fibers are affected by different environmental conditions, such as water exposure at elevated temperatures. Even when embedded in a matrix material, i.e., a thermoset or thermosetting polymer, exposure to moisture may occur. Therefore, in many structural applications of fiber-reinforced polymer composites, moisture may have a significant impact on the reinforcing elements and the rate of degradation. The present work focuses on the effects of hydrothermal aging on the mechanical durability of long carbon and basalt fibers by immersion in tap water at 60 °C, 71 °C, and 82 °C. A service life prediction model based on the Arrhenius technique was explored. Using this model, it is possible to forecast the amount of time that it takes to attain a given degradation level over a specified range of temperatures. The present study also investigated changes in tensile strength in response to exposure to 90% humidity at 90 °C. In addition, the chemical elements released during aging in water were determined. Fourier-transform infrared spectroscopy and mass dissolution studies were conducted to elucidate the mechanism causing strength losses. Scanning electron microscopy was employed to evaluate changes of the fiber surface morphologies due to hydrothermal exposure.