Molecular Weight–Dependent Reinforcement of Biobased Aromatic Thermoplastic Polyurethanes Using Vegetable Oil Crosslinkers

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Abstract
The transition toward sustainable thermoplastic polyurethanes (TPUs) is a key challenge for reducing the carbon footprint for a wide range of applications, from industrial to transportation, including advanced applications such as 3D‐printed sensors and soft actuators. In this study, a series of aromatic TPUs incorporating soy‐based crosslinkers with comparable hydroxyl functionality but different molecular weights were synthesized to elucidate the relationships among crosslinker structure, concentration, and isocyanate index. The use of a low‐molecular‐weight triol (92 g/mol) led to remarkable enhancements in mechanical performance, increasing the elastic modulus by 190% (up to 400 MPa) and tensile strength by 61% (up to 23.6 MPa) at only 2.5 wt%. Conversely, a high‐molecular‐weight triol (1000 g/mol) exhibited a soft plasticizing effect, reducing the modulus by 38% at 17.9 wt%. Despite these contrasting effects, Dynamical Mechanical Analysis (DMA) indicated that the addition of the biobased crosslinkers did not compromise reprocessability, while the isocyanate index was the dominant factor. These findings demonstrate the dual role of bio‐based crosslinkers, capable of either reinforcing or softening TPU matrices, offering a versatile design strategy to tailor thermomechanical performance while maintaining a biobased content exceeding 50 wt%.

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