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• Proposed a facile and eco-friendly modification method to graft CNTs onto titanium surface. • The interface between titanium and PEEK was interlinked by "coordination bridges" and CNTs network. • The interfacial shear strength between modified titanium and PEEK had an increment of 205.4 %. • The flexural strength (210.0 %), and ILSS (95.2 %) of modified CF/PEEK-Ti composites were significantly enhanced. The primary challenge of fiber metal laminates (FMLs) is the insufficient interfacial adhesion between metal and resin, which impedes the realization of the full potential. To address this issue, a two-step strategy has been proposed: firstly, via the cerium coordination-based approach, followed by grafting carbon nanotubes onto the titanium surface. This modification enhances the interfacial behavior between titanium sheets and polyetheretherketone (PEEK), resulting in increased roughness and wettability on the titanium surface, facilitating tight contact between PEEK and titanium sheets while reducing defects at the interface. Compared to CF/PEEK-sandblasted Ti, the modified CF/PEEK-Ti composites exhibit significantly enhanced interfacial shear strength, equivalent flexural strength, and interlaminate shear strength with an increase of 205.4 % (39.4 MPa), 133.3 % (1434.3 MPa) and 95.2 % (93.7 MPa), respectively. Additionally, the failure mode has shifted from interfacial failure to cohesive failure. The interface enhancement mechanism can be attributed to the synergistic effects of coordination bonding, mechanical interlocking, and multiple interactions. This facile two-step modification method demonstrates the potential to enhance the interfacial properties of CF/PEEK-Ti composites. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to the inert carbon fiber (CF) surface and the poor wettability of CF with poly(ether ether ketone) (PEEK), the fiber-matrix interface bonding of CF/PEEK composite is relatively weak, which limits the mechanical performance of the composite. Herein, a complex sizing agent containing Ti 3 C 2 T x MXene, carbon nanotube (CNT), and a dual compatibilizer of polyetherimide (PEI) was fabricated to graft on the CF surface. Compared with desized CF, the modified CF/PEEK composites showed a remarkable increase in flexural strength, flexural modulus, and interlaminar shear strength of 74.16%, 63.76%, and 62.79%, respectively. The improvement could be ascribed to the synergistic effects of multiple interactions, micromechanical interlockings, and substantially improved interfacial affinity by the hybrid grafting of MXene, CNT, and PEI. We also found that the interfacial failure mechanism changes from adhesive failure to cohesive failure with such a 1D/2D coating strategy. This facile and scalable approach demonstrates its potential for effectively improving fiber-matrix interfacial properties in CF/PEEK composites. [Display omitted] •A hierarchical structure containing 2D MXene, 1D CNT, and a dual compatibilizer of PEI was constructed on the CF surface. • The tensile strength of modified CF showed an appreciable improvement of 12.02%. • The ILSS (62.79%), flexural strength (74.16%), and flexural modulus (63.76%) of modified CF/PEEK composites were significantly enhanced. [ABSTRACT FROM AUTHOR]

The weak interfacial adhesion caused by the low wettability of carbon fiber (CF) and inert polyetheretherketone (PEEK) hinders the great application potential of CF/PEEK composites. In this study, the interface between CF and PEEK was modified by coating hydroxylated PEEK grafted onto multi-walled carbon nanotubes (M-HPEEK). Modified CFs by M-HPEEK sizing had rougher surfaces with more polar groups, showing decreased contact angle and increased surface energy. The wettability of these CFs was enhanced, beneficial to PEEK infiltration and physical adhesion improvement. As a result, the interlaminar shear strength, flexural strength, and flexural modulus of modified CF/PEEK composites were increased by 73.0% (84.7 MPa), 163.2% (906.2 MPa), and 84.8% (58.4 GPa), respectively. An improved interface with stress transferring was proved by the interface debonding failure changed to fiber crack and resin yield. M-HPEEK sizing is considered as a promising modification method to optimize the interface performance of composites. [Display omitted] [ABSTRACT FROM AUTHOR]