Improvement in interface and mechanical properties of CF/poly(ether-imide) and CF/poly(ether-ether-ketone) by aqueous sizing of reactive cationic Poly(amide-imide) with catechol pendant groups on CF

As automotive and aviation develop fast, Carbon fiber reinforced thermoplastic polymers (CFRTP) are increasingly welcomed. However, commercial sizings for CF, mainly epoxy, lack compatibility and thermal stability for high-performance thermoplastic composites. Current thermoplastic sizings are also inert for the CF surface. Therefore, here, poly(amide-imide) (PAI) with reactive catechol pendant groups were synthesized, which got rid of commercial surfactants in water dispersion due to the hydrophilia from ionizable quaternary ammonium salt pendant groups. Storage-stable aqueous sizing of highly soluble PAI was sized on CF, followed by preparations of CF/poly(ether-imide) (PEI) and CF/poly(ether-ether-ketone) (PEEK) composites. Mechanical properties considerably increased for the improved interface in composites contributed by the bridging of PAI sizing between CF surface and PEI, PEEK matrices. On one side, covalent bondings and intermolecular interactions were created between CF surface and PAI sizing. On the other side, π-π stacking and hydrogen bonding between PAI and PEI, PEEK was discovered. Compared to commercial-sized CF(cCF)/PEI, the interlaminar shear strength (ILSS), flexural strength and impact strength of pCF/PEI increased by 56.84%, 47.24%, and 48.87% to 100.22 MPa, 820.52 MPa, and 82.32 kJ/m 2 , respectively. • Aqueous quaternized poly(amide-imide) with reactive catechol pendant group was synthesized. • The poly(amide-imide) realized solubility and thermal stability simultaneously. • Aqueous CF sizing without surfactants was prepared by self-emulsifying of poly(amide-imide). • Covalent bonding between thermoplastic sizing and CF was realized for the first time. • Mechanical performances of CF/PEI and CF/PEEK composites were improved.