Lignin derived polyurethanes: Current advances and future prospects in synthesis and applications

Polyurethane (PU) owing to its excellent efficiency are well-designed product and extensively used in elastomers, coatings, foams, and adhesives. The use of natural and renewable raw materials such as lignin, which is primarily composed of phenylpropanoid that possesses a huge number of hydroxyl (OH) groups, phenols, and carbonyls has a promising capacity to substitute petroleum-based polyols in PU synthesis. The biological potential of chemically modified lignin showed better antibacterial, antioxidant, biocompatibility, flame retardancy, hydrophobicity, and UV-blocking properties that might be due to the addition of new functionalities. Numerous research has been carried out to incorporate lignin with currently accessible petroleum-based synthetic polymers using step-growth polymerization or blending method to overcome the challenges with lignin as a feedstock material. Different methodologies for the manufacturing of lignin-based polyurethane (LPU) are discussed in this review article, such as alkali treatment, oxidation method, prepolymer technique, haloalkane modification, alkane depolymerization, etc. This study covers recent advances in the development of lignin-based PU materials, with an emphasis on elastomers, films, coatings, foams, as well as in adhesives. Nowadays, lignin based polyurethanes have potential applications in construction, automated industries, packaging, textiles, footwear, supporting goods, automobiles, printing rollers, sealants, and binders.