Self-healing polyurethane coatings of eugenol-based polyol incorporated with linseed oil encapsulated cardanol-formaldehyde microcapsules: A sustainable approach

The development of eco-friendly materials is a major challenge tackled by preparing polymers of renewable origin as an alternative to the petroleum sources and by reducing repairing cost via formulating self-healing materials. In this study, cardanol and eugenol are used as renewable-phenols for the formulation of microcapsule based self-healing anticorrosive coatings. Cardanol was used to prepare microcapsules through an oil-in-water (O/W) emulsion system, whereas eugenol was utilized for the synthesis of polyester polyol by solvent-less melt condensation polymerization. The structure of polyol was confirmed by FTIR and NMR spectroscopies, while formation and surface morphology of microcapsules was confirmed by the FE-SEM. The thermal stability of microcapsules stood up to 232 °C as tested by TGA. The prepared microcapsules were dispersed in polyol formulations and crosslinked with methylene diphenyl diisocyanate to obtain self-healing smart PU coatings. The self-healing property of the prepared coatings was observed under FE-SEM. The developed coatings showed good physico-chemical properties such as gloss, crosscut adhesion, flexibility, pencil hardness, and MEK rub test. The corrosion resistance of the formulated self-healing coatings was found to be increased with increase in the quantity of microcapsules as studied by immersion and electrochemical methods.