Natural polyhydroxy resins in surface coatings: a review

The depletion of fossil fuels, high environmental pollution due to the release of toxic organic compounds, and high cost are some of the challenges regarding the reliance on petroleum-based resins. Natural polyhydroxy resins (from cashew nutshell liquid, castor oil, tannins, among others) are readily available, eco-friendly, low cost, and biodegradable, and offer enhanced properties when deployed on surface coatings. Accordingly, more attention has been paid to utilizing natural polyhydroxy compounds and bio-based polyurethane resins to replace synthetic resins in the last few decades. This review presents state-of-the-art natural polyhydroxy resins and their application as precursors in surface coatings. Bio-based resins from cashew nutshell liquid (cardanol), castor oil, and tannins employed as precursors in bio-based polyurethane coatings exhibit enhanced/excellent impact strength, adhesion, flexibility, water, and chemical resistance, to mention a few. Moreover, natural resins and eco-friendly polyurethane coatings, including their methods of modification, are also reviewed. This review article helps to promote natural polyhydroxy resins as sustainable and promising green materials for the coatings industry.