Processing window modification in PEEK through CO2 plasticization: Towards hierarchical additive manufacturing

Abstract

Poly(ether ether ketone) (PEEK) is a benchmark high-performance thermo- plastic, yet its high melting temperature, rapid crystallization kinetics, and narrow processing window severely constrain advanced manufacturing, especially additive manufacturing (AM). Here we demonstrate that dissolved CO₂ provides a powerful route to overcome these limitations through its plasticization effects. Dynamic mechanical analysis reveals a substantial 46 °C depression in T_g upon CO₂ saturation, together with a broadening of the transition regime from 20 °C to 60 °C, effectively widening PEEK’s processability window. This enables extrusion temperatures to be reduced by 20 °C. Moreover, CO₂ saturation induces up to threefold volume expansion during extrusion, with coarse cellular morphologies of approximately 100 µm. By coupling thermal plasticization with controlled foaming, this work lays the groundwork for CO₂-assisted PEEK processing strategies that enable processing at lower temperatures while introducing hierarchical architectures. These advances open new pathways for foam-based additive manufacturing of PEEK, expanding its design space for lightweight, high-performance applications in aerospace, medical, and beyond.