Natural polyhydroxy resins in surface coatings: a review

Abstract

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.