Elucidating nano and meso-structures of lignin carbon composites: A comprehensive study of feedstock and temperature dependence

The production of carbon materials from renewable biofeedstocks is rapidly expanding with commercial applications in the areas of advanced materials, energy storage, and biochemicals. Present-day challenges exist in understanding how the distribution of monomeric units in lignin feedstocks impacts the structure and properties of carbon composites as a function of processing. This research investigates the effect of lignin feedstock and processing conditions on the structure of carbon composites. X-ray data was collected at a synchrotron source for lignin from hardwood, softwood, and grass feedstocks, processed under varying temperature and environmental conditions. We report the relative abundance of the principal monomeric units—guaiacyl, p-hydroxyphenyl, and syringyl—varies with feedstock and result in reproducible variations in the x-ray data. Statistical analyses for over fifty carbon materials were performed to determine the influence of feedstock, reduction temperature, and furnace humidity. The changes in the pair distribution function correspond to changes in material structure. Taken together, the analyses support the observation that graphitic structures form and grow in size with increasing reduction temperature. The characteristic size of the graphitic crystallites varies with feedstock, with kraft softwood and organosolv switchgrass leading to carbon composites with larger graphitic domains.