Waste PET-Derived BHET as a Dynamic Architect for Biobased Self-Healing Polyurethanes with Tunable Strength and Reversible Adhesion

Abstract

Development of sustainable vitrimers that integrate both high mechanical properties and complete recyclability is still an abiding challenge owing to the conventional trade-off between permanent mechanical strength and network adaptability. In this study, biobased polyurethane vitrimers are synthesized using castor oil (CO) and bis(2-hydroxyethyl) terephthalate (BHET), a waste-derived aromatic diol from polyethylene terephthalate (PET), as a multipurpose network component. BHET simultaneously enhances the hard-segment network and incorporates a reversible ester–urethane linkage, enabling thermally stimulated network rearrangements. This integrated formulation yields a homogeneous, mechanically robust structure of vitrimer with a tensile strength of around 20.5 ± 0.5 MPa, along with rapid relaxation kinetics (τ* = 360 s at 160 °C), corroborated by effective thermal self-healing and enhanced reprocessability. Additionally, the optimized networks function as reversible hot-melt adhesives across diverse substrates, driven by the synergistic interplay of densely populated dynamic exchange sites, ester–urethane linkages, and hydrogen-bonded aromatic domains. Notably, they also exhibit excellent chemical resistance against various solvents and robust environmental stability under different conditions, while maintaining reversible adhesion over ∼10 cycles with minimal loss in performance. Collectively, this work couples plastic waste upcycling and biobased polyurethane networks with advanced vitrimer chemistry. These findings pave the way for a scalable design strategy that conquers the inherent conflict between reprocessability and durability of thermosets and offers next-generation biobased adhesives and structural materials.