Thermal Treatment of Aramid Fibers for Enhancing Pultruded Aramid Fiber Reinforced Polymer Rods: Competing Effects of Surface Activation and Weakening of Skin Layer

ABSTRACT This study proposes a tailored thermal treatment strategy to enhance fiber–resin interfacial interactions. Spectroscopic analyses reveal the surface activation mechanism of aramid fiber (AF), while the interlaminar shear strength (ILSS) and tensile strength of pultruded aramid‐fiber‐reinforced‐polymer (AFRP) rods are investigated under varying treatment temperatures and durations. The results indicate that thermal treatment induces the breakage of amide bonds in the main molecular chains of the AF skin layer, generating active functional groups such as amino and carboxyl groups, thereby enhancing AF surface activity and bonding with the resin. However, it also reduces the hydrogen bonding interactions between the main molecular chains, leading to weakening of intermolecular interactions in the AF skin layer and a decrease in longitudinal shear strength, consequently altering the ILSS and failure modes of the AFRP rods. With increasing thermal treatment time and temperature, the interfacial failure mode gradually evolves from AF‐resin interfacial debonding to AF skin layer fibrillar stripping, resulting in an initial increase followed by a decrease in ILSS; the tensile strength gradually decreased, especially over 240°C, while the failure mode and tensile modulus remained unchanged. Finally, an optimized thermal treatment (180°C–210°C, 5–7 min) was proposed.