Proanthocyanidins with Corrosion Inhibition Activity for AISI 1020 Carbon Steel under Neutral pH Conditions of Coconut ( L.) Husk Fibers.

L. is a palm tree (Arecaceae) with a high economic value. The coconut husk fibers are nonedible, thick, and abrasion-resistant and correspond up to 85% of biomass discarded as solid waste residue. Therefore, the husk fibers are an underexploited byproduct with a high content of extractives of unreported nature. Two varieties of L. husk extracts were investigated to uncover bioactive metabolites and their possible application as a green corrosion inhibitor for carbon steel AISI 1020 under neutral pH conditions. The chemical analysis indicated 3% (w/w) of proanthocyanidins in the husk fibers with a high B-type procyanidin content. The husk fibers' crude extract showed promising results as an eco-friendly corrosion inhibitor for carbon steel AISI 1020 under neutral pH conditions. Although it formed a film on the metal surface in all tested concentrations (0.4, 0.8, 1.2, and 1.6 g L), the highest protective efficiency was shown at a concentration of 1.2 g L, determined by electrochemical techniques and mass loss. This was the first comprehensive report on coconut husk fibers' chemical composition, which was similar between the two varieties with potential for industrial application.