Carbon Materials from Lignin and Sodium Lignosulfonate via Diisocyanate Cross-Linking and Subsequent Carbonization

Applications for lignin and lignosulfonates are limited today due to the undefined structure and varying properties of the substance. However, lignin, as the second most abundant bio-resource besides cellulose and the bio-resource with one of the highest natural carbon contents, has the potential to act as a precursor for carbon materials. In this study we have applied a Kraft lignin and a sodium lignosulfonate with the cross-linker toluene-2,4-diisocyanate. The reaction mixture was molded to form small cylindrical shaped paddings. Cross-linked lignin-polyurethane and lignosulfonate-polyurethane networks were analyzed via elemental analysis and thermogravimetric analysis and finally carbonized. The carbon material was analyzed for its BET surface area and its surface structure via scanning electron microscopy. Surface areas between 70 and 80 m2·g−1 could be reached. Moreover, the material was tested for its adsorption potential of crude oil from water and could take up to twice its own weight. For better understanding of the core chemistry of the cross-linking reaction, we have studied the reaction with model substances to define the reactive groups and the influence of sulfonate groups in the cross-linking reaction of lignin and lignosulfonates with toluene-2,4-diisocyanate.