A sustainable two-layer lignin-anodized composite coating for the corrosion protection of high-strength low-alloy steel

In this study, plasticized kraft lignin was used to prepare anti-corrosive coatings on steel, which was galvanostatically anodized (80 °C, 25 wt.% NaOH) by utilizing three different current density values (24, 50 and 120 mA/cm2). It was shown that the anodization affects not only the properties of anodic coatings but also their interaction with lignin coatings. A combination of pull-off adhesion measurements with linear sweep voltammetry (LSV) demonstrated an enhanced adhesion strength of plasticized lignin coatings (4.32 MPa on anodized surface vs. 2.38 MPa on bare steel) and decreased corrosion current density from 15 μA/cm2 (bare steel) up to ca. 0.5 μA/cm2 for anodized and lignin coated steel.