Development of Nanocrystalline Graphite from Lignin Sources

Authors: Garcia-Negron, Valerie; CHMELY, STEPHEN - Pennsylvania State University; ILAVSKY, JAN - Argonne National Laboratory; KEFFER, DAVID - University Of Tennessee; HARPER, DAVID - University Of Tennessee

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2022
Publication Date: 1/14/2022
Citation: Garcia-Negron, V., Chmely, S., Ilavsky, J., Keffer, D.J., Harper, D.P. 2022. Development of nanocrystalline graphite from lignin sources. ACS Sustainable Chemistry & Engineering. 10(5):1786-1794. https://doi.org/10.1021/acssuschemeng.1c05969.
DOI: https://doi.org/10.1021/acssuschemeng.1c05969

Interpretive Summary: Carbon-based materials are attractive for energy applications due to their unique thermochemical versatility but their complex structure is difficult to fully understand. Moreover, extraction of carbon from sustainable sources is desirable and an active area of research. This work evaluates the conversion of lignin, extracted from different plants, into carbon powders as a function of heating temperature. The microstructural evolution of lignin carbons is studied using x-ray scattering signals obtained from a high energy electronic source known as synchrotron. The resulting carbon powders show presence of amorphous and crystalline domains that depend on lignin type and processing temperature. Also, microstructural features across multiple length scales vary across the lignin carbons. Specifically, lignin carbons from softwoods have a higher degree of crystallinity than those from switchgrasses and hardwoods. This methodology provides a straightforward framework to evaluate the feasibility of leveraging lignin carbons for producing tunable application-specific materials.

Technical Abstract: Carbon composites are attractive to a variety of high-impact applications, such as carbon fibers, batteries, and vehicle parts, due to their multifunctional properties. The increase in demand for sustainable carbon sources motivates interest in understanding synthesis parameters of lignin value-added products. In this work, the thermochemical conversion of lignin powders from different feedstocks was evaluated via small and wide angle x-ray scattering techniques to resolve the amorphous, disordered, and crystalline domains present in the lignin carbons. Scattering analyses indicated an evolution of hierarchical structures along with an increase in ordered domains as a function of carbonization temperature. Qualitative and quantitative methods were used to describe isotropic scattering intensity profiles at multiple length scales. The use of power law models in the mesoscopic region served as the basis to describe morphological changes related to structural features, for example, graphene stacking, degree of roughness, and surface fractals. Kraft softwood and switchgrass produced carbon powder with the most crystalline domains and the least surface roughness. Softwoods reached the highest degree of crystallinity followed by switchgrass samples and attained less variability in particle sizes. Interpretation of x-ray scattering data from lignin carbon powders elucidates feedstock- and processing-dependent morphological features across multiple length scales providing a straightforward framework to evaluate the feasibility of leveraging lignin carbons for producing tunable application-specific materials.