Development and application of a high-performance underwater adhesive based on natural polyphenol/IPDI-modified epoxidized soybean oil

Achieving high-strength, durable adhesion in extreme humid or submerged environments has long been a challenge in materials science. Traditional adhesives failed to meet the requirements for rapid wetting, strong interfacial locking, and long-term stability due to issues like hydration layer interference, hydrolysis instability, and curing difficulties. This study proposed a novel ternary design using polyphenol/IPDI-modified epoxidized soybean oil (ESO) to develop a polyphenol-based soybean oil adhesive modified by gallic acid, tea polyphenols, and tannic acid (GTSO), as well as its IPDI-introduced crosslinked derivative (GTSO-I), for underwater adhesion. This system offers environmentally friendly properties, strong interfacial compatibility, high adhesion strength, rapid curing, and long-term stability. The system incorporates three natural polyphenols—gallic acid (GA), tea polyphenols (TP), and tannic acid (TA)—to form synergistic hydrogen bonds, coordination bonds, and hydrophobic interactions at the underwater interface. These polyphenols enable a ring-opening reaction with the epoxy moiety of epoxidized soybean oil (ESO), creating a chemical framework that provides strong adhesion to wet substrates. IPDI was then introduced to form a dense crosslinked network, enhancing curing speed and stability. Experimental results showed that GTSO-I achieved a shear strength of 4.50 MPa on steel substrates, surpassing most reported underwater adhesives. After 30 days of immersion, it retained over 93 % of its initial adhesion strength and maintained a shear strength of over 3.2 MPa across a broad pH range (1-13) and in 2.0 mol/L NaCl solution. The adhesive showed rapid curing underwater and was compatible with various substrates, demonstrating potential for applications in pipeline sealing, hull repair, and biomedicine.