Lignin Functionalized with Succinic Anhydride as Building Block for Biobased Thermosetting Polyester Coatings

Novel lignin-based thermosetting polyester (PE) coating systems are presented in this work. These new materials are based on the functionalization of a soluble fraction of softwood kraft lignin recovered from solvent extraction with increasing amounts of succinic anhydride (SAn), to obtain SAn/lignin adducts via the formation of ester bonds on the hydroxyl groups in lignin. A thorough chemical, physical, and thermal characterization of the resulting esterified materials was conducted to confirm the successful covalent incorporation of SAn in the lignin macromolecule. Such functionalized SAn/lignin adducts were employed as building blocks for the preparation of cross-linked lignin-based PE coatings under different curing conditions. These PE coatings highlighted improved thermal stability, film forming ability, solvent resistance, dynamic surface hardness, and higher hydrophobic character compared with the unmodified parent lignin precursor. In addition, the adhesion strength of these systems on different substrates was also assessed. The results of this study demonstrate an easily accessible approach to develop high-lignin-content thermosetting PE systems and provide evidence of the potential of these materials as bioderived coatings and adhesives.