• Adding an optimal amount of PEI to CNT/PEEK nanocomposites reduces melt viscosity by ~50%, significantly improving processability.
• Toughness is enhanced: strain to failure increases by 129% and fracture energy by 97%.
• The CNT/PEI powder blending method maintains thermal resistance while improving mechanical performance.
• The approach offers potential for PEEK powder laser sintering and thermoplastic prepreg production.