Self-Healing Polyurethane Coatings Incorporating Halloysite Nanotubes Loaded with Tannic Acid for Synergistic Corrosion Protection and Enhanced Mechanical Properties

Long-term metal protection can be aided by the intelligent release of corrosion inhibitors, which can improve organic coatings’ anticorrosion capabilities. In this study, halloysite nanotubes (HNTs) were vacuum-loaded with tannic acid (TA) and surface-modified via in situ polymerization of polypyrrole (PPy), yielding pH-responsive nanofillers (TA-PPy@HNTs). These nanofillers enabled controlled TA release, forming protective Fe–TA complexes at corrosion sites, while the outer PPy layer imparted photothermal responsiveness, facilitating disulfide bond exchange reactions and enhancing intrinsic self-healing capabilities. Furthermore, the incorporation of polydimethylsiloxane (PDMS) segments improved hydrophobicity and delayed corrosive ion ingress. The optimized PTH-3 coating exhibited excellent corrosion resistance, maintaining an impedance modulus above 108 Ω·cm2 after 90 days in 3.5% NaCl solution. It also demonstrated superior mechanical properties (elongation at break of 447.73% and tensile strength of 30.71 MPa), outstanding cavitation resistance, and efficient sunlight-driven self-healing, restoring over 90% of its mechanical performance after damage. This work provides a promising strategy for designing multifunctional, durable protective coatings for metallic substrates.