Fractionation of Industrial Softwood Kraft Lignin: Solvent Selection as a Tool for Tailored Material Properties

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.