Masters Theses

Date of Award

5-2017

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

David J. Keffer

Committee Members

David P. Harper, Orlando Rios

Abstract

Efforts to effectively use lignin, a by-product of paper and biofuels production, have been carried out for several decades. This renewable resource has potential for use as a carbonaceous material due to its aromatic structure and high carbon content, reminiscent of graphite. The search for new carbon-based materials is extremely active, because they are necessary components in many applications, such as energy storage, electronics, catalysis, and lubricants. Traditional carbon-based materials are derived or mined from petroleum or coal, thus, contributing to pollution, national security risks, and anthropogenic climate change. Lignin, a carbon-rich component found in the tissues of vascular plants, is commercially available as a waste product from pulp and biofuels industries. The main processing stages involved in converting raw lignin into a viable product are lignin extraction, carbonization treatments, physiochemical characterization, and application testing. Lignin is a complex amorphous macromolecule difficult to predict and these studies attempt to identify its processing-structure-property relationships. Due to the tremendous growth in demand for graphite, the United States is stimulating research efforts to produce and synthesize an alternate material.

The first part of this study involved processing kraft softwood lignin to make lignin-based anodes for low-cost, high-efficiency lithium-carbon batteries. The processing variables under investigation included the presence, temperature, and duration of thermal stabilization, pyrolysis, and reduction. Materials were characterized at the atomic- and micro-scales. Under optimal processing conditions, a coin cell with a lignin-based anode demonstrated capacity superior to the theoretical maximum capacity of 372 mAh/g [miliampere hour per grams] for graphite.

The second part of this study consisted on understanding structural relationships between green lignin feedstock and the resulting carbon composites, via a suite of characterization techniques. Small angle neutron scattering experiments were performed to understand and visualize structural orientation of green lignin fibers. Raman spectroscopy provided insight of the high degree of ordering and disorder of graphitic structure from carbonized fibers. Moreover, different types of lignin helped predict structural relationships between lignin sources, extraction methods, such as kraft and organosolv, and processing. These relationships dictate the resulting carbon structure, its mechanical properties, and its suitability for specific applications.

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