Enhancing interfacial solvent resistance and mechanical properties of carbon fiber/polyether ether ketone composites with water‐borne sizing agents based on cross‐linkable polyphthalonitrile

Abstract The inherent structural properties and elevated processing temperatures of thermoplastic resins present new challenges in the realm of carbon fiber (CF) sizing agents. Consequently, a water‐based cross‐linkable nitro‐phthalonitrile capped polyfluorenyl ether ketone sizing agent was meticulously designed. The sizing agent exhibits superior storage stability, encapsulating particles spanning dimensions from 66.51 to 87.71 nm. The inherent mechanism during the hot‐pressing stage involves a self‐crosslinking of nitrile groups toward stable structures with unparalleled resistance to solvents. The crosslinked sizing agent boasts a remarkable glass‐transition temperature of 290°C. Noteworthy, significance is the consequential 40.1% augmentation in maximum flexural strength, along with a commendable 35% increase in interlaminar shear strength for CF‐1.5/PEEK composites in contrast to their unsized CF/PEEK counterparts. In summary, the focal aspiration of this research endeavor lies in offering a straightforward and viable methodology for the exploration of cross‐linkable sizing agents, strategically catering to both “thermoplastic processing” and “thermosetting applications.” Highlights Bulky fluorenyl unit increases the intermolecular volume of copolymer poly(fluorenyl ether ketone). The introduction of the BPF unit to the molecular elevates the thermal stability of the copolymer. Unique electron‐donating proclivity of the fluorenyl group drastically improved its reactivity. The polymerization was accomplished at a relatively low temperature of 150°C for practical applications. The ILSS, IFSS, and bending strength were noteworthy increased by 35%, 74.02%, and 40.1%