Fabrication of three-dimensional polyetherimide bead foams via supercritical CO₂/ethanol co-foaming technology

The fabrication of light-weight and high-performance polymer foams, especially special engineering plastic foams, with complicate three-dimensional (3D) geometry remains a great challenge worldwide. In this study, microcellular polyetherimide (PEI) bead foams with 3D geometry and high expansion ratio were successfully prepared by using supercritical CO₂ (scCO₂)/ethanol (EtOH) as co-blowing agent. The co-foaming mechanism and the effect of EtOH on foaming properties were studied. The results indicated that the addition of EtOH increased the solubility of co-blowing agent in PEI matrix by promoting the interactions between them, thus broadening the foaming temperature window and significantly increasing the expansion ratio, up to 7.12. The obtained PEI foams with 3D geometry had the cell size of 58.54 μm and cell density of 3.66 × 10⁶ cells per cm³, as well as excellent mechanical strength, e.g., tensile stress of 6.59 MPa and compression stress of 6.87 MPa. This co-foaming technology also has a great potential in fabricating other high-performance polymer foams.