Haiming Chen,Zaizheng Sun,Kai Lu,Jinming Liu,Chaobin He,Dongsheng Mao
The mechanism behind the resilience of polymeric materials, typically attributed to the well-established entropy elasticity, often ignores the contribution of enthalpy variation (Δ H ), because it is based on the assumption of an ideal chain. However, this model does not fully account for the reduced resilience of thermoplastic polyurethane (TPU) during long-range deformation, which is mainly caused by the dynamics of physical crosslink networks. Such reduction is undesirable for long-range stretchable TPU considering its wide application range. Therefore, a negative Δ H effect is established in this work to facilitate instant recovery in long-range stretchable TPU, achieved by constructing a reversible interim interface via strain-induced phase separation. Consequently, the newly constructed dual soft segmental TPU shows resilience efficiency exceeding 95%, surpassing many synthetic high-performance TPUs with typical efficiencies below 80%, and comparable to biomaterials. Moreover, a remarkable hysteresis loop with a ratio exceeding 50%, makes it a viable candidate for applications such as artificial ligaments or buffer belts. The research also clarifies structural factors influencing resilience, including the symmetry of the dual soft segments and the content of hard segments, offering valuable insights for the design of highly resilient long-range stretchable elastomers.
In this work, we investigated the microphase separation, mechanical, and dynamic mechanical properties of thermoplastic polyurethane elastomers (TPUs) with one-soft segment (polypropylene glycol, PPG, or hydroxyl-terminated polybutadiene, HTPB) or bi-soft segment (PPG and HTPB) using FTIR, XRD, SAXS and amplitude modulated-frequency modulated viscoelastic mode of AFM (AM-FM mode AFM) methods. The results showed that the microphase separation process of hard and soft segments (HS and SS) in TPU containing PPG and HTPB soft segments (PPG-HTPB-PU) was restricted by randomly alternated bi-soft segments, which results in formation of a low content of irregular-shaped hard domain (HD). In addition, the microphase separation of PPG-HTPB-PU induced a triple-phased structure of HD, HTPB rich phase and mesophase. The mesophase of PPG-HTPB-PU was formed of HS, PPG and HTPB segments which were excluded out of HD and HPTB rich domains during microphase separation process. The damping temperature range (at tan δ greater than 0.3) of PPG-HTPB-PU was from −14.6 to 32.1°C (46.5°C) which was more broad than that of TPU containing HTPB soft segment (HTPB-PU). The broad damping temperature range of PPG-HTPB-PU is mainly attributed to the enhanced energy consumption caused by the frictional motions of mixed segments of mesophase.
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