Dual-factor decoupling Strategy: Independent quantification of crystallization and infiltration effects in PAEK-sized CF/PEEK composites

While interfacial enhancement in carbon fiber/polyether ether ketone (CF/PEEK) composites typically involves coupled mechanisms, the specific contributions of each mechanism remain poorly quantified. In this study, infiltration and crystallization are systematically decoupled and quantified by using poly aryl ether ketone (PAEK) sizing agents with controlled molecular weights (2000–8000) and distinct crystallization behaviors (para-crystalline and meta-amorphous). The roles of infiltration kinetics and interfacial crystallization are isolated by synthesizing PAEK polymers with identical chemical structures but varying intrinsic viscosities and crystallinities. Results reveal that crystallization contributes a consistent interfacial shear strength (IFSS) enhancement of approximately 26 MPa, nearly independent of molecular weight. In contrast, infiltration enhancement increases inversely with molecular weight, increasing from 13 MPa to 32 MPa as intrinsic viscosity decreases. Synergistic optimization achieves a record IFSS of 110.02 MPa in CF/PEEK composites. This work establishes a dual-factor decoupling strategy for quantifying interfacial mechanisms and provides a scalable approach for high-performance thermoplastic composite design.