Polyurethanes from Recovered and Depolymerized Lignins

Aldehyde-Assisted Lignocellulose Fractionation Provides Unique Lignin Oligomers for the Design of Tunable Polyurethane Bioresins

“…In this context, lignin has long been considered a renewable aromatic macropolyol that could potentially replace conventional fossil-derived polyols in PU synthesis because of its high concentration of hydroxyl groups (both aliphatic and phenolic) that could react with isocyanates to achieve PU linkages. However, despite the long history of lignin PU synthesis, several issues are still preventing the more widespread integration of lignin in PU products . The synthetic challenges for designing lignin PU are well known and are generally attributed to (1) the low solubility of lignin (in solvents or with the other PU precursors), resulting in its poor incorporation into the polymer matrix, in low reactivity with the co-reactants, and the impossibility to use common organic solvents, (2) the high molecular weight of lignin, which creates steric hindrances, further limiting its reactivity, (3) its high polydispersity, which leads to inconsistent performance, reactivities, and solubilities, (4) its sulfur content that can generate odor problems and yellowing of final products, and (5) lignin’s dark color that prevents its use in certain applications including coatings.…”