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Eco-friendly cardanol-based polyurethane coating provides superior corrosion protection for steel
An Indian research team has developed a hydrophobic, waterborne polyurethane (WBPU) coating derived from the bio-based raw material cardanol. Combining high solid content with outstanding corrosion and chemical resistance, the formulation avoids toxic crosslinkers and adheres to green chemistry principles.
The demand for renewable raw materials in coating technologies continues to rise. Researchers led by Shiva Sharma have synthesised an environmentally friendly, hydrophobic waterborne polyurethane (WBPU) coating using cardanol, a by-product of the cashew industry. The resulting nano-dispersion contains 75.5 % solids and was produced without additional crosslinkers following green chemistry principles.
Varying the amine content (10–25 %) significantly influenced the mechanical and anticorrosive performance. FTIR analysis confirmed complete polymer curing, while transmission electron microscopy (TEM) revealed uniform spherical particles with a diameter of 7 ± 3 nm. The coatings exhibited a dense, rough amorphous morphology, improving their barrier efficiency.
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Excellent resistance and corrosion performance
Mechanical tests demonstrated scratch hardness of 2 kg, high impact resistance (150 lb/in), bending flexibility (1/8 inch), and 100 % crosshatch adhesion. Chemical resistance tests with 3.5 % HCl, NaCl, NaOH, solvents, and water showed no significant degradation. The formulation containing 20 % amine achieved optimal performance with strong hydrophobicity and thermal stability up to 230 °C.
After 24 days of immersion in 3.5 % NaCl, the coating exhibited 98.98 % corrosion inhibition efficiency, confirming its excellent barrier properties. The cardanol-based WBPU coating thus represents a sustainable, high-performance alternative to conventional polyurethane coatings for metal protection.
Source: Sharma, S. et al. Development of environment-friendly cardanol-derived hydrophobic anticorrosive high solid waterborne nano-dispersed polyurethane coatings. Prog. Org. Coat. 207, 109402 (2025).
