Vegetable oil-based polyurethane coatings: recent developments in India

The present review centers on the preparation of polyurethane (PU) from vegetable oils as a renewable resource for formulating coatings. More precisely, the focus is on the contribution of India in PU coatings based on vegetable oils, as vegetable oils are available on a large scale and agriculture is the backbone of the Indian economy. The increase in the applications of vegetable oils in polymer preparation is due to the fluctuation in prices, uncertainty in supply and depletion of petroleum sources. Out of all vegetable oils, a majority of edible-grade oils are used in food-based products, while their non-edible counterparts are available on a large scale for exploring other applications. Industrial chemicals, in particular polyols for PU, can be obtained by chemical modifications of vegetable oils. These modifications involve etherification, esterification, epoxidation, thiol-ene reactions, neutralization and so on. The product - that is, polyol - of such modified oils can be low-molecular-weight resins - namely, alkyds, polyesteramides, polyetheramides and so on. Their structures can be controlled with hydroxyl chain ends and can be used in PU. The importance of such polyols has been confirmed in formulating PU coatings as well as in smart materials such as self-healing coatings.