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New lignin-based thermoset polyurethane (PU) coatings with high lignin content are presented in this work. These materials were obtained by extracting a sol fraction from a raw kraft lignin sample with the bioderived solvent 2methyltetrahydrofuran (MeTHF), and subsequently directly cross-linking the MeTHF-soluble lignin fraction with a toluene diisocyanate (TDI)-based polyisocyanate at different weight ratios. A thorough characterization of the PU materials highlighted their improved thermal stability, better film forming ability and higher hydrophobic character compared with the un-cross-linked lignin precursor. Additionally, force− distance curve measurements by atomic force microscopy were employed to determine the elastic modulus of the PU materials. Finally, the lignin-based PU materials were found to exhibit high adhesion on different substrates, including glass, wood and metals. The results of this study demonstrate that the direct reaction of chemically unmodified fractionated lignin with polyisocyanates represents an interesting strategy for the development of lignin-based thermoset PU systems that may find application in the field of high-performance biobased coatings and adhesives.

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A simple approach for the fractionation of industrial softwood kraft lignin is presented in this work aimed at predictively obtaining readily usable lignin fractions with tailored material properties in a straightforward manner. This method is based on the use of three distinct solvents of different chemical nature to isolate soluble and insoluble fractions from the parent lignin by a single-step extraction process. A thorough characterization of the soluble and insoluble lignin fractions highlighted a direct correlation between the chemical-physical characteristics of the extraction solvent and the final properties of the recovered materials. In particular, hydrogen bonding interactions between solvent and lignin were demonstrated to play a major role in the extraction process, controlling to a great extent the final materials properties. The results of this study give a clear demonstration of a straightforward approach to access easily lignin fractions with well-defined characteristics and provide strong evidence of the direct correlation between solvent characteristics and properties of the extracted materials as predictive tool for the development of high-performance lignin-based systems. (Figure Presented)

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