Hygrothermal aging behavior and aging mechanism of carbon nanofibers/epoxy composites

In this study, carbon nanofibers (CNFs)/epoxy composites incorporating different contents of CNFs were fabricated and immersed in distilled water for 180 days. Water absorption test, tensile tests, scanning electron microscopy (SEM) observation, dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) spectroscopy were performed to evaluate the effect of CNFs content on hygrothermal aging behavior of CNFs/epoxy composites, and to reveal the hygrothermal aging mechanism of such composites. Test results showed that the addition of CNFs into pure epoxy resin could obviously improve its hygrothermal aging behavior. The CNFs/epoxy composites had better resistance to water absorption than pure epoxy because CNFs improved the water barrier properties of the composites. The improvements of glass transition temperature and the storage modulus of the composites before and after aging were attributed to the fact that the addition of CNFs limited the loosening of molecular chains and increased the second cross-link density of epoxy resin. FTIR spectroscopy showed that the number of –OH functional groups of CNFs/epoxy composites was decreased, which revealed that CNFs inhibited the hydrolysis of epoxy resin and water absorption. This study demonstrates that adding appropriate amount of CNFs into epoxy resin has potential to improve the long-term durability of epoxy-based composites in hygrothermal environment.