Enhanced interfacial and mechanical properties of carbon fiber/PEEK composites by hydroxylated PEEK and carbon nanotubes

The interfacial adhesion between carbon fiber (CF) and polyetheretherketone (PEEK) is poor due to their inert nature, limiting the mechanical properties of CF/PEEK composites. This study improved the interactions between CF and PEEK by sizing hydroxylated PEEK grafted multi-walled carbon nanotubes (HPEEK-g-MWCNT) synthesized via an esterification reaction. Molecular dynamics simulations and experiments were conducted to evaluate the microstructure and characterize the mechanical properties of CF/PEEK composites. A slightly decreased crystallinity of PEEK within modified composites resulted from the reduced nucleation effect of CF and inhibited PEEK mobility by HPEEK-g-MWCNT sizing. Hydrogen bonding and mechanical interlocking enhanced interface adhesion, and covalent bonds of HPEEK-g-MWCNT increased load transfer. These factors led to the flexural strength and interlaminar shear strength of HPEEK-g-MWCNT modified composites increased by 94.2% (669.7 MPa) and 55.2% (79.1 MPa) compared with control ones. The modification method of using chemically treated and grafted polymers like HPEEK-g-MWCNT would have great potential applications in thermoplastic composites.