Conversion of biomass lignin to high-value polyurethane: A review

Lignin, as a major by-product of pulp and paper industry, has attracted extensive interest for the preparation of high value-added products, due to the merits of abundant, sustainable, inexpensive, and unique functional groups. This review focuses on the strategies to develop high performance polyurethane (PU) materials from lignin on the basis of main reports, in which lignin was used not only as macromonomer to substitute petroleum-based polyols, but also as blending filler for PU industry. Pre-treatment approaches, especially lignin fractions extracted with various solvents and chemical modifications, e.g., depolymerization, hydroxyalkylation, dealkylation, and esterication, were widely explored to enable lignin more reactive and available to synthesize PU products. In addition, lignin/PU blends were also prepared to fulfill industrial demand. With adjustment of lignin structure, the PU formulation, and synthesis procedures, various lignin-based PU products with advanced properties and a higher bio-substitution ratio have been developed, demonstrating the potential industrial application of lignin for high value-added sustainable materials.