Table 1.

Potential challenges for integration of lignins into polyurethane (PU) products and possible mitigation approaches.

Lignin Property	Impact on PU Synthesis or Performance	Potential Solution
Sulfur content	Odor problems in final product, yellowing in coating applications	Selection of appropriate lignin source
Low solubility	Poor incorporation into polymer matrix and low interaction with the co-reactant (NCO)		Depolymerization or fractionation of the lignin	Functionalization of the lignin
Low reactivity	Poor incorporation into polymer matrix
High Tg	Brittleness
High polydispersity	Inconsistent performance, differing reactivities and solubilities
Dark color	Limited utility in some coating applications where light color is required
Ultraviolet (UV) instability	Product degradation in outdoor applications	Ensuring the reaction between isocyanate and lignin phenolic hydroxyl groups; Addition of UV stabilizers