Controlling Energy Dissipation during Deformation by Selection of the Hard-Segment Component for Thermoplastic Polyurethanes

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In this work, two typical commercial thermoplastic polyurethanes (TPUs), one polycaprolactone-based TPU (step-polymerized with 1,5-naphthalene diisocyanate (NDI), coded as TPU-NDI) and another polytetramethylene ether glycol-based TPU (step-polymerized with 2,4-toluene diisocyanate (TDI), coded as TPU-TDI), were chosen to explore the dependences of energy dissipation during deformation on the microstructures of TPUs. The chemical compositions and microphase morphologies were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, transmission electron microscopy, and atomic force microscopy. Thermal and mechanical tensile properties were measured by using thermogravimetric analysis and monotonic tensile deformation test. Energy dissipation was estimated by the area of the “hysteresis circle” in a cyclic tensile process. The in situ small-angle X-ray scattering technique was applied to investigate the microstructural evolutions during cyclic tensile deformation. It is found that the selection of suitable hard segment domains plays a key role in controlling the energy dissipation of TPUs during deformation.