The use of lignin as the most abundant aromatic natural polymer has been evaluated for use in the production of lignin-based polyurethane resin for coating applications. Coatings are made of resins (ca. 50%), which today are mainly derived from petroleum-based polymers. This study is focused on the development of an environmentally friendly method of modifying lignin to be used as source of natural polyols. Lignin contains both aliphatic and aromatic hydroxyl functional groups and it can be used as a sustainable source of polyol for reaction with isocyanate to form polyurethane resin. However, limited accessibility of hydroxyl groups in lignin is a major problem in promoting the application of lignin as polyol. In this study, organosolv lignin samples (hardwood and softwood) were modified by using a bromide-based ionic liquid. The analysis of lignin samples with phosphorus nuclear magnetic resonance spectroscopy (31P NMR) before and after modification showed significant increase in the hydroxyl contents of both hardwood and softwood organosolv lignins. As a result, the modified lignins had shown higher reactivity with polyisocyanate used in the study which was also confirmed by Fourier Transformed Infrared (FTIR) spectra of samples. This novel modification method will increase the potential application of lignin as source of natural polyol for production of polyurethane (PU) resins.

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