Thermal Oxidation Activation for Precise Control of Interfacial Physicochemical Structures in <scp>3D</scp> ‐Printed Continuous Carbon Fiber/Polyamide Composites

ABSTRACT 3D‐printed continuous carbon fiber‐reinforced polyamide (CCF/PA) composites suffered challenges in achieving strong interfacial adhesion due to rapid melting‐cooling and limited impregnation pressure during layer‐by‐layer deposition. To address this, a thermal oxidation activation strategy was proposed to enhance the mechanical properties of 3D‐printed composites by precisely controlling the interfacial evolution behavior of carbon fibers (CF). The interaction between the physical structure and chemical polarity of CF and their effects on the mechanical properties of 3D‐printed CCF/PA composites were systematically examined. The results indicate that the mechanical properties of 3D‐printed composites are collectively governed by the interfacial morphology of CF and graphite‐induced microdefects. Under the constrained thermal and pressure conditions of 3D printing, the surface chemical polarity critically influenced interfacial construction efficiency. The controlled oxidation has introduced surface defects, altering the stress‐transmission pathways and their effectiveness. Furthermore, the orientation and content of the graphite structure on the carbon fiber surface determine the conversion efficiency of the mechanical properties in 3D‐printed composites. This study illustrates the mechanism by which CF interfacial evolution contributes to the mechanical behavior of 3D‐printed CCF/PA composites, providing insights for interfacial design in additive manufacturing of high‐performance composites.