Synergistic cooperation of a Magnolol-based waterborne cross-linkable PEEK sizing agent and click chemistry to construct exceptional solvent-resistance and interfacial properties of CF/PEEK composites

Despite the impressive strides on waterborne cross-linkable sizing agents for carbon fiber (CF)-reinforced polyether ether ketone (PEEK) composites, the vast majority of polymer precursors employed for sizing agents in existing researches are derived from petroleum resources. On the other hand, the notable influence of the adhesive strength between sizing agent and CF on the interfacial properties of composites has been consistently disregarded. Herein, a waterborne cross-linkable sizing agent was prepared capitalizing on naturally existing magnolol. Meanwhile, sulfhydryl groups were chemical-grafted on the surface of CF via click reaction, setting stages for subsequent interaction with magnolol units via a second click reaction to effectively enrich the force between CF and sizing layer. As a unique feature of the system, the inherent mechanism of the sizing coating layer comprises self-crosslinking of the orchestrated propenyl groups toward sturdy structures during hot-pressing, contributing to unrivalled solvent-resistance and unorthodox interfacial robustness. As a result, the bending strength, interlaminar and interfacial shear strength of the derived composites were promoted by 35.48 %, 47.87 % and 61.03 %, respectively. Noteworthy, the mechanical properties of Sized-CF composites were well-preserved after solvent aging treatment. Therefore, this protocol developed a novel bio-based waterborne cross-linkable sizing agents of PEEK derivative, laying a good foundation for advanced CF/PEEK composites with excellent interfacial performance.