Fast and Green Biomineralization Strategy to Tailor Rigid‐Flexible Coupling Interphase for High‐Performance Carbon Fiber Reinforced Epoxy Composites

ABSTRACT The weak interfacial adhesion between carbon fibers (CFs) and the epoxy (EP) matrix remains to represent a fundamental limitation in developing high‐performance CF/EP composites. In this study, we constructed a hierarchical interphase on CF surfaces using seaweed‐derived sodium alginate (SA). By exploiting the ion‐exchange reaction between SA and Ca ²⁺ to form a dense “egg‐box” chelation structure, a stable, ionically cross‐linked calcium alginate (CaAlg) network was robustly anchored onto CF surfaces. Notably, the biomimetic mineralized layer enhanced the surface characteristics of CFs. In particular, the surface roughness increased from 405 nm to 474 nm, thereby providing an effective template for mechanical interlocking. X‐ray photoelectron spectroscopy revealed a substantial increase in oxygen‐containing functional groups, with the carboxylate content rising from 1.0% to 10.2%, resulting in a 59.8% increase in surface free energy. Consequently, the interlaminar shear strength and flexural strength of the resulting CF/EP composites were 74.81% and 73.81% higher, respectively, compared to those of untreated CF/EP composites. Mechanistic analysis revealed that the improvement in interfacial performance originated from the synergistic contributions of enhanced mechanical interlocking and physicochemical interactions between the CaAlg network and the EP matrix. Overall, this research provides a scalable, green, and highly efficient strategy for engineering advanced interphase in CF‐reinforced polymer composites.