In Situ Bead Fusion Induced by Elevated Foaming Temperatures\nand Compressive Forces during Constrained Bead Expansion

Bead\nfoams, lightweight materials produced from expandable or expanded\nbeads, are widely used in industries, including automotive, consumer\ngoods, and packaging. Traditional molding methods, which separate\nfoaming from molding, increase both the production complexity and\ncycle time. This study demonstrates a simple one-step in-mold foaming\nand molding (IMFM) method, effectively achieving strong in situ bonding\nof polymer beads due to elevated foaming temperatures and compressive\nforces during constrained bead expansion. Constrained expansion resulted\nin increased cell wall thickness and greater tortuosity of the gas\ndiffusion pathway in the bead foams, ensuring structural stability\nat high temperatures. High hardness thermoplastic polyurethane molded\nparts were obtained using IMFM and the molded parts with a density\nof 0.184 g/cm<sup>3</sup> exhibited a tensile strength of 1.51 MPa\nand an elongation at break of 181.1%. The IMFM shows significant promise\nfor producing bead foam parts from high-performance polymers, owing\nto its straightforward bead fusion process and freedom from molding\ntemperature restrictions.