Molecular Engineering of Polyimide Sizing Agents with Ether and Sulfone Groups for Tailored Interfacial Performance in CF/PASS Composites

Abstract The interfacial adhesion between carbon fibers and polymer matrices critically determines the mechanical performance of fiber-reinforced composites, yet achieving strong bonding remains a persistent challenge. A molecular engineering strategy is developed to tailor the fiber-matrix interphase in carbon fiber-reinforced poly(arylene sulfide sulfone) (PASS) composites by designing three sizing agents: poly(amic acid) (PAA) and its thermally imidized polyimide derivatives bearing either ether or sulfone groups. Through a combined experimental and computational approach, the influence of the chemical structure of the sizing agents─specifically, the nature of the groups (ether vs sulfone), and the postimidization state-on interfacial adhesion and failure behavior is systematically investigated. The results demonstrate that the sulfone-containing polyimide sizing agent exhibits superior interfacial reinforcement, which is attributed to its strong intermolecular interactions with the PASS matrix, including hydrogen bonding as well as π-π stacking enabled by its rigid, conjugated chain architecture. This leads to a marked enhancement in mechanical performance: tensile strength, interlaminar shear strength, and interfacial shear strength increase by 43.9%, 115.2%, and 101.5%, respectively, compared to desized CF, accompanied by a transition in failure mode from interfacial debonding to cohesive failure within the matrix and fiber fracture. Moreover, the interfacial layer thickness reaches 445 nm, and complementary simulations (finite element analysis, molecular dynamics, and density functional theory) confirm the correlation between sizing-induced adhesion and interfacial failure characteristics. This work clarifies the distinct roles of ether/sulfone architectures and PAA imidization in enhancing the CF/PASS interphase, providing theoretical and experimental guidance for engineering high-performance fiber composites.