Interfacial and mechanical enhancement of short carbon fiber–reinforced PEEK composites via polyetherimide modification

Short carbon fiber (SCF) reinforced polyetheretherketone (PEEK) composites were prepared via a polyetherimide (PEI)-assisted solution filtration followed by hot pressing, and the effect of PEI introduction on interfacial behavior and mechanical performance was systematically investigated. PEI-modified SCFs were obtained by immersion in PEI/DMF solutions with concentrations of 0-1.5 wt% and subsequently combined with PEEK powders to fabricate SCF/PEI/PEEK composites. The results show a pronounced non-monotonic dependence of mechanical properties on PEI content. Compared with the unmodified SCF/PEEK composite, the composite containing 0.5 wt% PEI exhibits the best overall performance, with tensile strength increasing from 124 MPa to 142 MPa and flexural strength from 205 MPa to 272 MPa, while the fracture toughness is slightly improved from 17.5 to 18.3 MPa·m^1/2. In contrast, excessive PEI addition (1.5 wt%) leads to a significant deterioration of mechanical properties. FTIR and XPS analyses confirm the successful introduction of PEI-related functional groups onto the fiber surface, while SEM and AFM observations reveal increased surface roughness and distinct changes in fiber surface morphology after PEI modification. Fracture surface analysis indicates a clear transition in interfacial failure features with PEI content, suggesting improved stress transfer at moderate PEI levels. Molecular dynamics simulations provide qualitative support for the experimental observations by revealing stronger interfacial interactions in the SCF/PEI/PEEK system. These results demonstrate that controlled PEI introduction is an effective approach to regulate interfacial characteristics and enhance the mechanical performance of SCF/PEEK composites.