From Fiber to Composite: In Situ Addition of Graphene Oxide Driven Structural and Mechanical Improvements in PBO

Abstract The high mechanical strength of the fiber and efficient load transfer between the fiber and matrix are critical for the application of fiber‐reinforced composites. In this work, Poly(p‐phenylene benzobisoxazole) (PBO) with an ultra‐high tensile strength of 7.58 GPa is successfully synthesized by the addition of a small amount of graphene oxide (GO). The outstanding mechanical properties are effectively transferred to the composites, achieving tensile strengths of 6.53 GPa in the impregnated fibers. Multi‐scale characterization combine with molecular simulations revealed that the addition of GO promotes the alignment of molecular chains along the axial direction, thereby enhancing the fiber strength. Simultaneously, the 2D structure of GO enhances multiscale interfacial interactions among molecular chains, nanofibrils, and microfibril bundles, thereby strengthening radial cohesion within the fiber. The improved radial interactions contribute to maintaining structural integrity under mechanical loading, mitigating premature failure, and ultimately enhancing the mechanical performance of the composite. This advancement offers valuable insights and practical guidance for the development and application of high‐performance fibers.