Mechanism of Multi‐Scale Interface Bonding in <scp>PVDF</scp> ‐Modified Continuous Carbon Fiber Reinforced <scp>TPU</scp> Composites

ABSTRACT Strengthening the interfacial bonding between continuous carbon fiber (CCF) and the matrix, as well as minimizing defects, is crucial for advancing rapid prototyping of complex load‐bearing components and enhancing performance. Investigating the combination mechanisms across atomic, microscopic, and macroscopic multi‐scale interfaces can help overcome the bottleneck characterized by “strong fibers–weak interfaces” in carbon fiber reinforced composites (CFRP). In this paper, we present a pretreatment strategy involving the impregnation of CCF with polyvinylidene fluoride (PVDF) solution, followed by wet twisting. This approach aims to enhance the mechanical properties of CCF filaments, improve interfacial characteristics, and reduce pore defects in printed components. The impregnation process parameters and the wet twisting procedure were optimized through orthogonal experiments, elucidating the mechanism of interface bonding at the fiber scale. Subsequently, the interfacial bonding between the molecular chain layers of PVDF and TPU was simulated. By investigating hydrogen bonds, van der Waals forces, Coulomb interactions, total weak interactions, and the evolution of interfacial system density, we explored the regulatory mechanisms governing molecular chain mobility and interfacial bonding strength within this system at various printing temperatures. Furthermore, the XCT non‐destructive characterization method was employed to investigate the impact of the aforementioned processes on the interface bonding and internal porosity of the printed components from a macroscopic perspective. This indicates that the process is effective in reducing pore defects within the printed part and enhancing interface bonding performance.