Impact of Epoxy Resin Modification Using a Tannic Acid‐Based Additive on Hydrothermal Durability of Carbon Fiber Reinforced Polymers

The long‐term performance of carbon fiber–reinforced polymers (CFRPs) is governed by the evolution of the fiber–matrix interface and the changes in matrix properties under service conditions. This work studies the impact of epoxy modification using an additive (TA‐AGE), prepared by the chemical modification of tannic acid (TA) with allyl glycidyl ether (AGE), on CFRP properties and their long‐term evolution in hydrothermal aging environments. The resin modification with 1 wt% TA‐AGE additive increased polar functional groups, which enhanced the CFRP interface by forming more hydrogen bonds. As a result, the mechanical properties of the CFRP, such as interlaminar shear strength (ILSS) and flexural strength, increased by 31.9% and 8.5%, respectively, without significantly affecting the glass transition temperature ( T g ). Accelerated aging studies performed in water at 20°C, 40°C, and 60°C showed that the resin modification increased the water uptake characteristics of CFRPs. This increased the plasticization effects and resulted in more degradation in ILSS and flexural properties during the early stages of aging compared to CFRPs with an unmodified matrix. However, the CFRPs with the TA‐AGE modified matrix retained higher mechanical properties, with equilibrium moisture content, after 3 months of aging.