Synthesis and modification of non-isocyanate thermoplastic polyurethane (TPU) from recycled waste electrolytes

Abstract

To realize green, high-value recycling of spent lithium-ion battery electrolytes and avoid isocyanate-based polyurethane toxicity, this study developed a non-isocyanate route for the green synthesis of thermoplastic polyurethane (TPU) via waste utilization. The low-boiling electrolyte-derived substances reacted with aromatic diamines as hard-segment diamino carboxylate precursors, while the high-boiling components condensed with dimethyl succinate (DMSu) to yield four hydroxyl-terminated polyethylene succinate (PES) prepolymers (M_η: 518.26, 1007.98, 1534.77, and 2023.62 g mol⁻¹) by adjusting the reaction time. A green catalyst system consisting of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and sodium methoxide (2 : 2 : 1) produced eight unmodified non-isocyanate TPUs, with the PES-2-based sample showing the best overall performance despite its insufficient tensile strength. Orthogonal experiments using ethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, and renewable isosorbide (ISB) as chain extenders optimized the modification process, generating high-performance products 1,8-TPU-17 and 1,4-TPU-18. Characterized by FT-IR spectroscopy, ¹H/¹³C NMR, GPC, DSC, TGA, universal testing machine, DMA, and Materials Studio simulations, TPU had the expected structure, including T_g values of −19.36 to −20.56 °C, T_d,5% values of 184.09 to 253.64 °C, tensile strength values of 16.31 to 17.36 MPa, and elongation at break values of 438% to 451%. Isosorbide boosted chain rigidity, cohesive energy, and hydrogen bond density, with “O–H⋯OC” bonds supporting performance improvement. This work combines waste recycling and green polymer synthesis, offering eco-friendly and industrially scalable solutions.