Ionic aqueous quaternized Poly(amide-imide) sizing on CF for improving interface and mechanical performance of CFRTP

With the rapid development of automotive, aviation, and aerospace, Carbon fiber reinforced thermoplastic polymer (CFRTP) has been widely used. However, massive commercial surfactants were used in present aqueous sizings for CF in high-performance CFRTP since thermoplastic polymers in sizing were all hydrophobic, which resulted in thermal instability and mechanical performance decrease. To solve this problem, herein, quaternary ammonium salt groups were introduced to poly (amide-imide)(PAI) via click-reaction, a novel quaternized PAI with excellent solubility and thermal stability was synthesized. An aqueous thermoplastic CF sizing was prepared via self-emulsifying of quaternized PAI without surfactants for the first time, which was stable after 12-month-storage. Furthermore, PAI-sized CF with appropriate processability was obtained for the manufacture of CF/PEI (polyether-imide) and CF/PEEK (polyether-ether-ketone) composites. Mechanical performances and hydrothermal aging resistance of composites were all significantly improved. Especially, quantum chemical calculations were employed to reveal the mechanisms of interface strengthening in composites, there were hydrogen bonding and π-π stacking between PAI sizing and PEI, PEEK matrix.