Urethanes, lignin-based

Reactions of alkoxylated lignin with diisocyanates produce thermoset materials because the lignin polyol is always polyfunctional with a functionality greater than 2. The isocyanate-alcohol reaction produces a urethane linkage that when repeated creates a crosslinked, nonreformable polyurethane. This is shown in Fig. 6. A broad spectrum of lignin-based urethanes have been made and tested. The data show that these materials match if not exceed the properties of synthetic polyurethanes made without lignin [60]. 

Adhesive properties are listed in Table IX. Shear strength, wood failure, and swelling data for two wood species, southern pine and hard maple, illustrate excellent performance properties of lignin-based urethane products. 

Urethane coatings for wood surfaces, prepared with lignin-based polyester-ether-polyol, have demonstrated exceptional properties in terms of solvent and chemical resistance (18), and they provide the coated wood surface with an attractive appearance. 

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