“Lock–anchor chain” structure inspired double-crosslinked interface for improving the interfacial adhesion of CF/PEEK composites

A novel approach was developed to overcome the issue of weak interfacial adhesion in carbon fiber/polyether–ether–ketone (CF/PEEK) composites, combining surface modification via sizing with diazotization chemistry. In this “lock–anchor chain” structure–inspired design, carboxylated PEEK served as the “chain” and naphthyl groups introduced via esterification acted as the “anchor,” successfully yielding a waterborne crosslinkable PEEK-NAP sizing agent for enhancing interfacial interactions. In addition, the naphthyl groups are chemically grafted onto the surface of CF by diazotization reaction, functioning as a “locking mechanism” that enabled interactions with the anchor chain. Introduction of naphthalyl design markedly improves the interfacial interaction between the sizing agent and the CF. The distinguishing characteristic of this system manifests in the thermally induced self-crosslinking of naphthyl moieties during hot-pressing, resulting in a robust and stable structural framework. This framework imparts exceptional solvent resistance and unconventional interfacial stability to the composites. Experimental findings indicate that the implementation of this “lock–anchor chain” strategy engender marked enhancements in mechanical performance, with significant increases of 63.4% (flexural strength), 53.0% (interlaminar shear strength), and 82.3% (interfacial shear strength). These improvements are primarily ascribed to the synergistic effects of mechanical anchoring and interfacial bonding facilitated by the anchor-shaped PEEK-NAP sizing agent. Notably, even after solvent aging, modified CF composites retain their excellent mechanical properties.