Sustainable PET-derived zwitterionic gels reinforced by ionic liquids for flexible electronic skin sensors

The transformation of waste polyethylene terephthalate (PET) into high-value functional materials remains a key challenge for sustainable polymer circularity. Here, we report a sustainable PET-derived zwitterionic gel in which phosphonium-based ionic liquids modulate the network through ion-dipole and ion-ion interactions, while the PET-based polyurethane functions as a structural regulator providing additional hydrogen-bond anchoring. The deep-eutectic betaine/Zn(OAc) 2 solvent serves as an efficient catalyst for PET glycolysis, enabling sustainable conversion of PET into polyurethane precursors. The ionic liquids act as dynamic cross-linking centres that densify chain packing, enhance charge transport, and facilitate stress delocalization throughout the dual network structure. When combined with the PET-PU-derived hydrogen-bond framework and MXene fillers, the gel preserves high conductivity and integrity in the presence of large deformation. The optimized gel exhibits a high toughness (486.9 kJ m −3 ), 856% elongation, ultralow modulus (0.078 MPa), and a high adhesion (245.8 kPa), which is similar to, or even higher than, human skin. The gel can be used as a flexible electronic-skin sensor that has a wide strain range (0–856%), high sensitivity (maximum gauge factor of 4.24 in the high-strain region), a detection limit of 0.5%, and stability of more than 1000 cycles. This work highlights ionic-liquid-induced dynamic cross-linking as a key mechanism governing mechanical and electrical performance, establishing a sustainable PET upcycling strategy for next-generation soft bioelectronic materials.