Evolution of ordered structure of TPU in high-elastic state and their influences on the autoclave foaming of TPU and inter-bead bonding of expanded TPU beads

Different from the melt foaming of extrusion and injection molding, polymer is in high-elastic state during autoclave foaming. In this study, the critical parameters used to describe the high-elastic state of polymer, i.e., softening temperature (Ts) and viscous flow temperature (Tv), were introduced to explain the autoclave foaming of thermoplastic polyurethane (TPU) and the inter-bead bonding mechanism of expanded TPU (ETPU) beads. Evolution of ordered structure of TPU in high-elastic state was characterized by different methods. The steamchest molding was used to manufacture the ETPU parts, and the molding temperature window was compared with the Ts and Tv of TPU resin, and the endothermic peaks of ETPU beads. The melting of ordered hard segments structure, interface-diffusion of polymer chains, cooling-induced formation of new ordered structure among the diffused polymer chains were the possible mechanism of strong inter-bead bonding in the molded ETPU parts