Carbon Dioxide-Blown Expanded Polyamide Bead Foams with Bimodal Cell Structure

Bead foam has received substantial attention in recent years because of its high expansion ratio and ease of formability. Currently, most commercially available bead foams are produced from commodity plastics, and not many engineering polymers are used for this. In this study, the potential of polyamide 6 (PA 6), a typical engineering polymer, for bead foam applications was investigated by batch foaming. PA 6 was blended with its own copolymer to create double melting peaks for foam sintering. Chain extenders such as styrene maleic anhydride and Joncryl ADR 4368 C were added to improve the melt strength. After foaming, a crystal structure with double melting peaks was formed. In addition, the foam possessed a bimodal/nanocellular structure, and the foamed beads could be sintered. This is the first report of bead foam manufacturing using engineering plastics without toxic solvents. These results provide insights for bead foam research.