Development of a Bio-Inspired Self-Healing Polymer Coating System for Corrosion Protection of Steel Infrastructure in Nigerian Coastal Environments

Corrosion of steel infrastructure in the coastal environments of South South and South West Nigeria causes annual economic losses estimated in the billions of naira, with conventional protective coatings providing limited autonomous repair capability when mechanically damaged. This research develops a bio-inspired self-healing polymer coating system for steel infrastructure, incorporating microencapsulated healing agents and intrinsic reversible polymer network architectures to enable autonomous damage repair in the humid coastal environment of Lagos and Rivers states. Three self-healing mechanisms are investigated: microencapsulated epoxy-amine healing agent release, Diels-Alder reversible cross-linked polyurethane networks, and boronic acid-diol dynamic covalent polymer systems. Healing agents were encapsulated in urea-formaldehyde and melamine-formaldehyde microcapsules characterised for size distribution, shell thickness, and rupture force by atomic force microscopy. Coating films were applied on steel substrates and mechanically damaged by controlled scratch, followed by healing under ambient temperature and UV activation as appropriate to each system. Electrochemical impedance spectroscopy and salt spray testing monitored corrosion protection restoration after damage-healing cycles. A computational model of healing agent diffusion and reaction was developed to predict healing efficiency as a function of capsule density and healing agent viscosity. Results demonstrate that microencapsulated epoxy-amine system achieved 87 percent recovery of electrochemical impedance after 24 hours healing at 35 degrees Celsius, representative of Nigerian coastal ambient temperatures. The Diels-Alder system achieved 94 percent impedance recovery after UV activation but required 60 degrees Celsius thermal stimulus for retro-Diels-Alder bond reformation. The boronic acid system provided multiple healing cycles with 72 to 81 percent efficiency retention per cycle. The research provides the scientific basis for developing self-healing protective coatings for critical steel infrastructure in Nigerian coastal zones. Keywords: self-healing polymer, corrosion protection, microcapsule, coastal environment, steel infrastructure