Bio‐based semi‐aromatic waterborne PIEK‐C sizing agent to construct a robust interface for CF/PEEK composites

Abstract Despite the impressing advances on sizing agents for CF/PEEK composites, the aromatic backbone of the polymer precursors utilized in the vast majority of reports compromises the dispersity and ductility of the slurry, subsequently resulting in inferior overall performance of the composites. Meanwhile, most resins employed for sizing agents in existing reports are based on petroleum resources. Herein, a bio‐based waterborne sizing agent utilizing semi‐aromatic poly ether ketones (PIEK‐C) derived from isosorbide and phenolphthalein has been disclosed, featured by its salutary dispersity, exceptional thermal stability, higher glass transition temperatures, and broader applicability. Due to the structural similarity between the sizing and resin matrix, the protocol endowed CF/PEEK composites with ameliorated overall performance, addressing issues related to inadequate adhesion of CF with PEEK resin, as well as environmental pollution commonly associated with existing commercial epoxy and solvent‐based sizing agents. The T g and T 5% of PIEK‐C‐5050 were 205.08 and 427.16°C, respectively. The particle size range of the PIEK‐C sizing agents spanned from 66.32 to 84.63 nm. The flexural strength and interlaminar shear strength of the composites experienced a respective 993.92 MPa (30.73%) and 83.32 MPa (36.97%) increase compared to untreated CF/PEEK composites following sizing treatment with PIEK‐C‐5050, underscoring expedient intermolecular interactions based on comparable solubility and π‐π stacking effects between the PEEK and PIEK‐C components. This study introduced an efficient and eco‐friendly approach to enhance the interfacial properties of CF/PEEK composites. Highlights PIEK‐C resin is employed for the first time to prepare carbon fiber sizing agents. The PIEK‐C sizing agent significantly fortified the surface energy and wettability of carbon fibers. The CF/PEEK composites after treatment with PIEK‐C sizing agent showed excellent heat resistance. The ILSS and bending strength of the composites were significantly increased by 36.97% and 30.73%, respectively.