Synergistic effect of hydrogen bonding and π-π stacking in interface of CF/PEEK composites

Due to the extraordinary thermal stability, chemical resistance and processability, carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites are widely applied in aviation, aerospace, medical fields, etc. However, the non-polar nature and low wettability of CFs limited the interfacial bonding between CFs and PEEK and results in unsatisfied mechanical properties for CF/PEEK composites. In order to enhance interactions between fibers and matrix, the interface in CF/PEEK composites was built through coating a mixture of polyetherimide (PEI) and functionalized multi-walled carbon nanotubes (COOH-MWCNTs) on CFs. The combination of hydrogen bonding between COOH-MWCNT and PEI as well as the π-π interaction between PEI and PEEK significantly improved the miscibility and interfacial interlocking. As a result, the flexural strength, modulus and interlaminar shear strength (ILSS) of modified CF/PEEK were remarkably improved by 76% (667.8 MPa), 119% (40.0 GPa), and 85% (90.7 MPa) respectively. The failure mechanism changed from smooth cracking in interface destruction to zigzag cracking and resin breakage, suggesting that the resultant interface became strong enough to ensure efficient stress transfer from PEEK to CF. The synergistic interfacial interactions via hydrogen bonding and pi-pi stacking are believed to supply an effective strategy for building high-performance thermoplastic composites.