Characterization of Fractions Obtained from Two Industrial Softwood Kraft Lignins

Abstract

With increasing interest in using lignin as an alternative material to petroleum-based chemicals (e.g., in the manufacture of carbon fibers or adhesives), it is becoming important to understand what properties of lignin are required to impart key features in the final product. Commercial lignins are complex, heterogeneous, macromolecular mixtures. To obtain maximum value, lignins will require classification and possibly fractionation or modification to improve properties and enable their utilization in high-value applications. To this end, the physicochemical properties of fractions derived from two industrial softwood Kraft lignins (New Bern Mill, Weyerhaeuser, U.S.A., and Backhammar Mill in Kristinehamn, Sweden) have been determined and compared to previously published data on commercially available Indulin AT lignin from MeadWestvaco., The fractions were obtained by successive extraction with organic solvents and analyzed using a range of techniques (e.g., DSC, ¹³C NMR, ³¹P NMR). The results showed that these industrial softwood Kraft lignins varied significantly in both the amounts of the various fractions and in the properties of the analogous fractions. These differences emphasize the issues industry faces in the utilization of industrial lignins for high-value applications where minor inconsistencies between lignin sources could pose major technical challenges