Examination of how variations in lignin properties from Kraft and organosolv extraction influence the physicochemical characteristics of hydrothermal carbon

Seven different lignin samples, three from Kraft extraction and four from organosolv extraction, were subjected to hydrothermal treatment at 260? for four hours to assess the impact of lignin type on the physicochemical properties of the hydrothermal material. The 13C Solid state NMR, XPS, FTIR and SEM analysis revealed that the different sources of lignin and the extraction conditions created variations in the degree of syringyl and guaiacyl subunits, inter-unit bonding arrangements, morphology and surface composition. Hydrothermal carbonization appeared to ?normalize? the differences between each of the lignin samples, via breaking ?-O-4 or ?-O-4 linkages, removal of methoxy and syringyl subunits, and creation of C?C and 4-O-5 linkages to polymerization into large 100-200 ?m amorphous carbon particles. Overall, this study indicates that the source and extraction type have minimal influence on the physicochemical structure and morphology of the final hydrothermal product.