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

Bead foams, lightweight materials produced from expandable or expanded beads, are widely used in industries, including automotive, consumer goods, and packaging. Traditional molding methods, which separate foaming from molding, increase both the production complexity and cycle time. This study demonstrates a simple one-step in-mold foaming and molding (IMFM) method, effectively achieving strong in situ bonding of polymer beads due to elevated foaming temperatures and compressive forces during constrained bead expansion. Constrained expansion resulted in increased cell wall thickness and greater tortuosity of the gas diffusion pathway in the bead foams, ensuring structural stability at high temperatures. High hardness thermoplastic polyurethane molded parts were obtained using IMFM and the molded parts with a density of 0.184 g/cm3 exhibited a tensile strength of 1.51 MPa and an elongation at break of 181.1%. The IMFM shows significant promise for producing bead foam parts from high-performance polymers, owing to its straightforward bead fusion process and freedom from molding temperature restrictions.