Formulation and Performance Evaluation of a Bio-Based Hybrid Epoxy Coating for Metal Protection in Aqueous Aggressive Environment

Abstract

Conventional coating consisting of toxic material (hexavalent chromium, lathanide salt) pose serious health and environmental risk. In response to the global demand for a more sustainable alternative, we developed a sustainable eco-friendly epoxy coating using a bio-based organic – inorganic hybrid comprising of Dacryodes edulis leaf extract (DE) and precipitated amorphous silica (PAS). DE was obtained via cold extraction while PAS was synthesised by neutralization reaction between sulphuric acid and sodium silicate. FTIR and GC-MS analysis confirmed the presence of functional groups including O-H, C=C, and aromatic esters. SEM, TEM and XRD analysis validated successful DE/PAS hybridization and the amorphous nano scale nature of PAS. Raman and FTIR on coatings confirms a well cured epoxy network. Environmental evaluation test (Salt spray and UV radiation /weathering test) in 5 wt% NaCl revealed superior barrier performance of the hybrid coating over epoxy only and single additive systems. Electrochemical studies confirmed enhanced corrosion resistance of the hybrid  system,  low corrosion current (1.3 × 10⁻⁶ mA/cm²), high pitting (−0.26 V) and repassivation (0.27 V) potentials, narrow hysteresis width  (0.01 V) and, high charge transfer resistance (352 Ω·cm²), and lower admittance values (Yo1 = 1.179×10⁻⁴, Yo2 = 1.541×10⁻⁴) and stable capacitive behaviour hese findings highlight the potential of DE/PAS hybrids as eco-friendly, high performance additive for protective coatings and is suitable for demanding application in marine, aerospace and structural industries.