Doctoral Dissertations
Date of Award
12-2020
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Materials Science and Engineering
Major Professor
David P Harper
Committee Members
David J Keffer, Orlando Rios, Claudia Rawn
Abstract
This work focuses on establishing a comprehensive understanding of lignin-derived materials as a function of carbonization with the goal of identifying processing-structure-property-performance relationships. A combination of modeling, statistical, and empirical materials characterization techniques are applied to lignin materials varying in feedstock source, extraction method, and processing conditions. The first part of this study evaluates the structure of carbon composite materials, possessing both crystalline and amorphous domains, using scattering techniques. One approach performs atomistic simulations of a proposed structure, from which the analogous scattering pattern can be obtained for validation. An alternative approach based on a hierarchical decomposition of the radial distribution function is used to generate a physics-based model allowing rapid interpretation of scattering data. The model is compared with atomistic simulation results in order to demonstrate that the contributions of the crystalline and amorphous domains, as well as their interfaces, are correctly captured. 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. The effect of lignin feedstock and processing conditions on the structure of carbon composites is studied. X-ray data was collected at a synchrotron source for lignin from hardwood, softwood, and grass feedstocks, processed under varying temperature and environmental conditions. The changes in the pair distribution function correspond to changes in material structure and it supports the observation that graphitic structures form and grow in size with increasing reduction temperature. The third part of this study resolves the structure of lignin carbon composites using small and wide angle x-ray scattering techniques. The study will help describe particles and aggregates in the lignin carbon structure. In this experiment complementary SAS techniques helps visualize voids and lignin structure as function of carbonization. Ultimately, this work enriches the understanding of controlling lignin feedstocks derived carbon product to support and develop products from systems that are sustainable and based on renewable resources. Results will help tune lignin carbon production to enable high-quality materials with targeted nanostructure for application in areas that are rapidly expanding such as advanced materials, energy storage, and biochemicals.
Recommended Citation
Garcia Negron, Valerie, "Engineered Carbon Materials With Nano-Graphitic Domains Derived From Lignin. " PhD diss., University of Tennessee, 2020.
https://trace.tennessee.edu/utk_graddiss/6071