Acetylated lignin as a biocomponent for epoxy coating — Anticorrosive performance analysis by accelerated corrosion tests

Carbon steel is one of the main metallic materials used in the manufacture of products in various sectors of society. The high susceptibility of this material to the corrosive process makes it necessary to use mechanisms to protect it from corrosion, with the use of epoxy coatings being one of the main methods. However, in harsh environments, the anticorrosive ability of epoxy coatings weakens. Therefore, there is a growing number of studies of compounds to be used as additives in the development of anticorrosive coatings. This work uses Kraft lignin, a waste from the pulp and paper industry, as a bio-additive for epoxy resins to be used in the corrosion protection of carbon steel when exposed to severe corrosion environments. For this, accelerated corrosion tests of salt spray, ultraviolet weathering, and saturated humidity were carried out. The epoxy-lignin coatings were obtained by incorporating acetylated lignin (AKL) in the diglycidyl ether of bisphenol-A resin (DGEBA). The curing agent for the coatings was isophorone diamine (IPDA). Two types of epoxy-lignin coatings were prepared, namely: DGEBA/7.5% AKL, and DGEBA/15%AKL. The structural characterization of the coatings was evaluated by Fourier transform infrared spectroscopy (FTIR). The physicochemical properties of the coatings were analyzed by testing contact angle, gel content, water vapor transmission, and ion permeation. The anticorrosive properties of the coatings were evaluated by electrochemical impedance spectroscopy (EIS). The performance of coatings with acetylated lignin was compared with the epoxy coating without acetylated lignin and the corrosion protection mechanism of epoxy-lignin coatings was proposed. The results indicate that the addition of acetylated lignin improves the resistance of the coatings against corrosion, as demonstrated by higher impedance values and capacitive behavior in the accelerated corrosion tests. Additionally, the coatings with acetylated lignin exhibit better performance in blocking the migration of Na+ and Cl− ions, further slowing down the corrosion process.