Abstract

Increased corrosivity of biodiesel toward metallic components has motivated the search for environmentally friendly corrosion inhibitors. However, studies investigating plant extracts as inhibitors in biodiesel systems remain limited, particularly for babassu biodiesel. In this work, the ethanolic extract of Myracrodruon urundeuva (“Aroeira-do-Sertão”) leaves was investigated for the first time as a green corrosion inhibitor for AISI 4340 carbon steel exposed to babassu biodiesel. Static immersion tests were conducted for 2592 h (108 days) at 45 °C, and the inhibitory performance was compared with that of the commercial antioxidant Trolox™. Corrosion behavior was evaluated by gravimetric weight loss measurements and surface morphology analysis using scanning electron microscopy. Phytochemical screening, FTIR, and 1H NMR spectroscopy revealed the presence of phenolic compounds, flavonoids, and tannins containing hydroxyl functional groups and conjugated aromatic systems. The 1H NMR spectrum exhibited characteristic signals in the δ 6.6–6.4 ppm region, which were attributed to aromatic protons of phenolic compounds and flavonoids, while signals between δ 5.4 and 4.9 ppm indicated vinyl and olefinic protons associated with unsaturated secondary metabolites. These findings are consistent with FTIR results, confirming the presence of hydroxyl-rich phenolic structures and conjugated systems capable of promoting adsorption onto the metal surface. The extract exhibited a corrosion inhibition efficiency of 89%, significantly higher than that obtained with Trolox™ (27.9%). SEM analysis confirmed a substantial reduction in surface degradation in the presence of the extract. These results demonstrate the strong potential of Myracrodruon urundeuva leaf extract as a sustainable corrosion inhibitor for metallic materials in biodiesel environments.

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