Enhancing inter-bead bonding of PEBA bead foams by boosting interfacial diffusion during in-mold foaming and molding

Abstract

Polyether block amide (PEBA) foams have attracted considerable attention in advanced footwear technology, owing to their low density and exceptional resilience. However, existing research predominantly focuses on block-type PEBA foams, with relatively limited investigation into bead foam molding techniques. Herein, we introduce an in-mold foaming and molding (IMFM) strategy, where low-melting-point ethylene-vinyl acetate (EVA) was blended with PEBA to overcome the challenge of poor inter-bead bonding in pure PEBA bead foam parts. The molten EVA acts as an effective interfacial adhesive during the IMFM process. This is demonstrated by a fundamental shift in the fracture mode: from inter-bead failure in pure PEBA parts to intra-bead fracture in the PEBA/EVA blends. Consequently, the optimal formulation with 5 wt% EVA achieved a low density of 0.107 g/cm³ and a high rebound resilience of 73.8 %, coupled with a 15 % increase in tensile strength (to 0.63 ± 0.04 MPa) and an 84 % increase in elongation at break (to 137 ± 6.6 %). Furthermore, the confined nature of the IMFM process generates sufficient internal pressure to stabilize the cellular structure, preventing cell collapse. This straightforward strategy offers a scalable and feasible approach for the mass production of high-performance PEBA bead foam products.