Development of a sustainable anti-corrosive coating from human hair waste-derived crude melanin

Corrosion remains a persistent global challenge, causing severe economic losses and material degradation across multiple industries, while the accumulation of human hair waste poses an emerging environmental burden due to its slow biodegradation and widespread disposal. Addressing these two pressing issues simultaneously, this study presents a sustainable strategy that transforms waste human hair into a value-added anti-corrosive coating material. Crude melanin was extracted from human hair via a base hydrolysis method and subsequently incorporated into a biodegradable poly(vinyl alcohol) (PVA) matrix with different melanin: PVA ratios to develop an eco-friendly coating. Successful extraction and characteristic functional groups of melanin were confirmed using Fourier Transform Infrared (FTIR) Spectroscopy. The corrosion protection performance of the developed coating was evaluated using Tafel polarization and Electrochemical Impedance Spectroscopy (EIS). The Tafel polarization revealed a substantial enhancement in corrosion resistance, achieving an inhibition efficiency of 89.4% for a 4000 ppm crude melanin coating compared to bare stainless steel. Furthermore, the study demonstrates the practical feasibility of the approach, where approximately 5.000 (±0.001) g of hair waste can produce sufficient crude melanin (12,000 ppm) to coat an 8 × 8 inch stainless steel surface with a thickness of 0.10 ± 0.01 mm. Unlike previous studies employing synthetic or microbial melanin, this work demonstrates the use of minimally processed crude melanin extracted directly from waste human hair as an environmentally sustainable anticorrosive coating material, providing a practical waste-to-value strategy for corrosion protection.