Tuning the Properties of Bio-based Thermoplastic Polyurethane Derived from Polylactic Acid by Varying Chain Extenders and Hard Segment Contents

Currently, the preparation and application of bio-based thermoplastic polyurethane (TPU) are hot research topics in the field of polyurethane. In the present work, a series of polylactic acid (PLA)-based TPUs were synthesized using bio-based PLA and 4,4'-methylene diphenyl diisocyanate (MDI). The effects of three chain extenders, including 1,3-propanediol (PDO, PD), 1,4-butanediol (BDO, BD), and 1,6-hexanediol (HDO, HD), on the characteristics and properties of PLA-based TPUs were investigated. The successful synthesis of PLA-based TPUs was confirmed by the absence of isocyanate groups and the presence of characteristic peaks corresponding to urethane and other functional groups. The analyses revealed the potential for greater crystallization in the PLA-BD and PLA-HD series. Among the examined groups, the PLA-HD variant with a 55% hard segment content displayed the highest molecular weight and fracture stress, and an appropriate elongation value, indicating its suitability for specific applications. The study also investigated the stress relaxation rates and residual forces and found them to be within clinically acceptable ranges. These findings demonstrate the potential of these synthesized TPUs for orthodontic applications, with the ability to tailor mechanical properties by adjusting hard segment contents and modifying chain extenders.