Foaming of polymers with supercritical fluids and perspectives on the current knowledge gaps and challenges

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.

Light-weight and three-dimensional PEI bead foam products with microcellular structure and good mechanical properties fabricated by self-designed mould assisted scCO₂/ethanol co-foaming technology.

Characterization of Different Chemical Blowing Agents and Their Applicability to Produce Poly(Lactic Acid) Foams by Extrusion

This study presents the applicability of different types (exothermic and endothermic) of chemical blowing agents (CBAs) in the case of poly(lactic acid) (PLA). The amount of foaming agent is a fixed 2 wt%. We used a twin-screw extruder and added the individual components in the form of dry mixture through the hopper of the extruder. We characterized the PLA matrix and the chemical blowing agents with different testing methods. In case of the produced foams we carried out morphological and mechanical tests and used scanning electron microscopy to examine cell structure. We showed that PLA can be successfully foamed with the use of chemical blowing agents. The best results were achieved with an exothermic CBA and with PLA type 8052D. The cell population density of PLA foams produced this way was 4.82 × 105 cells/cm3, their expansion was 2.36, their density 0.53 g/cm3 and their void fraction was 57.61%.