Designing thermal annealing to control mechanical performance of thermoplastic polyurethane elastomers

Abstract

The use of thermoplastic polyurethane (TPU) films as a lightweight elastomer has grown continuously over the years due to their good mechanical properties and excellent chemical and corrosion resistance. Yet, the high-temperature mechanical performance of TPU elastomers needs to be improved for extending their application as metal counterparts. In this study, we design a facile post-processing thermal treatment (i.e. annealing) to control the mechanical performance of TPU films under a possible temperature rise during operation. For this purpose, the TPU films, prepared by compression molding of commercially available TPU granules, are annealed at different temperatures (i.e., 60, 120, and 180 °C) and times (i.e., 24 h and 1 week). The results reveal the effectiveness of annealing to enhance the creep behavior and storage modulus at high temperatures. In the meantime, the room temperature tensile properties of annealed samples remain almost unchanged, offering unique applications for the TPU elastomers often used at room temperature, while they may face a temperature increase up to a certain value during operation. The dual effect of annealing on structural evolution of TPUs (i.e., formation of new crystallites and slight rearrangement of hard segment rich domains) are also discussed through differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS) characterizations, and atomic force microscopy (AFM).