Corrosion-Resistant Coatings from Renewable Resources: Preparation, Characterization, and Performance

Introduction: The increasing importance of eco-friendly materials has accelerated demand for renewable resources for coating applications. Bio-based polymer coatings with enhanced protective properties have emerged as a promising alternative to conventional coatings by combining high renewability and sustainability. This study focuses on the preparation and characterisation of corrosion-resistant coating formulations synthesized from sustainable and renewable feedstocks - epoxidized soybean oil (ESBO) and itaconic acid.

Methods: A hydroxyl-functional polyester was synthesized through the ring-opening reaction of epoxidized soybean oil (ESBO) with itaconic acid. The resulting polymer was cured using two different mechanisms: reaction with a renewable isocyanate to produce a polyurethane coating and photoinitiator-assisted UV curing to produce a UV-cured coating system. The chemical structure and surface morphology of the synthesized polymer coating were characterized using Fourier-transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FE-SEM). The developed coatings were further evaluated for mechanical, surface, and corrosion-protective properties, including pencil hardness, scratch hardness, adhesion, gloss, water contact angle, flexibility, impact resistance, electrochemical impedance spectroscopy (EIS), and salt spray testing.

Results: The coating formulations exhibited a pencil hardness ranging from 2H to 4H, a scratch hardness of at least 2 kg, and an adhesion rating of 5B. The coatings also demonstrated excellent gloss, with values exceeding 90 gloss units, and a water contact angle of more than 80°, indicating good surface hydrophobicity. Furthermore, the coatings showed satisfactory flexibility, impact resistance, and enhanced corrosion resistance, as confirmed by EIS and salt spray testing.

Conclusions: The results demonstrate that both renewable-isocyanate-cured polyurethane and UV-cured systems exhibited promising mechanical, surface, and corrosion-resistant properties. This study emphasizes and supports the potential of sustainable alternatives to petroleum resources in corrosion-protective coatings. Keywords: sustainable coatings; epoxidized soybean oil; itaconic acid; UV-cured coating; bio-based polyurethane; corrosion resistance.