Dopamine-grafted polyurethane adhesives derived from glycolyzed PET: Toward sustainable and high-performance underwater bonding

Polyurethane (PU) adhesives hold significant promise for interfacial applications due to their tunable soft-hard segment design. However, the sustainability of conventional PU adhesives is constrained by their reliance on petroleum-derived feedstock, while their adhesion strength is significantly undermined in humid or underwater environments due to competitive interfacial water. Herein, we report a two-step strategy that integrates the glycolysis of waste polyethylene terephthalate (PET) with bio-inspired dopamine grafting to fabricate a catechol-functionalized polyurethane adhesive with robust and repeatable wet adhesion. Waste PET was first glycolyzed and the product was purified via silica gel column chromatography. The resulting glycolytic liquid product (GLP) was employed as a chain extender. Dopamine was then grafted onto the PET-based polyurethane backbone to introduce catechol functionalities, yielding a dopamine-grafted adhesive (C-GPUD). The catechol groups not only interact with urethane groups via hydrogen bonding but also undergo conformational adaptation, oxidative cross-linking, and metal chelation. These synergistic effects collectively enhance both the cohesive strength and the interfacial bonding. The optimized C-GPUD 10 adhesive exhibited rapid and robust adhesion on various substrates in underwater scenarios. It demonstrated excellent repeatable adhesion in tap water, retaining a lap shear strength of 0.21 MPa after ten peeling cycles, which corresponds to 45.7% retention of the initial strength. This outstanding performance enables C-GPUD to effectively seal liquid and gas leaks, demonstrating considerable potential for applications in emergency sealing and underwater repair.