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Title Carbon Fibers Derived from Dry-Spinning of Modified Lignin Precursors
Publication Date
Degree PhD
Discipline/Department Chemical Engineering
Degree Level doctoral
University/Publisher Clemson University
Abstract Cost and environmental concerns arise from the manufacture of carbon fibersusing petroleum-based precursors such as polyacrylonitrile (PAN). Toxic by-productssuch as hydrogen cyanide (HCN) are generated during stabilization and carbonization ofPAN-based carbon fibers. These concerns have promoted increasing interest in biomass-based carbon fibers. As the second most abundant biomass material on the earth, lignin isbeing investigated as a potential carbon fiber precursor. Therefore, this research wasfocused on converting lignin materials into carbon fibers with enhanced performanceproperties. Since the 1960s, various types of lignin have been investigated as carbon fiber precursors. Hardwood kraft lignin and organosolv lignin could be converted into carbon fibers without chemical modification, whereas softwood kraft lignin was very difficult to convert without suitable modification or plasticization. Strength of most of the carbon fibers produced from the above lignin precursors were below 800 MPa, which is much lower than that of commercial carbon fibers derived from PAN precursors. Thus, the overall goal of this study was to produce lignin-based carbon fibers with enhanced mechanical properties by a scalable process. The specific objectives were to: (i) identify different types of lignin precursors for their potential of being carbon fiber precursors; (ii) study the modified lignin-acetone solutions to establish a range of suitable combinations of solution concentrations and spinning temperatures; (iii) establish thermal stabilization and carbonization conditions for lignin-based precursor fibers to enhance the performance of resulting carbon fibers; and (iv) to develop a UV/thermal dual stabilization route to increase the speed of stabilization. The lignin precursors investigated in this study included an organosolv lignin, a soda lignin, and a softwood kraft lignin. The organosolv lignin was successfully melt-spun into fibers without any modification of the precursor material. However, it took more than 200 hours for the thermo-oxidative stabilization step. The infusible soda lignin was chemically modified by acetylation into a fusible material, but it could not be cross-linked. The softwood kraft lignin was modified by a similar acetylation reaction and fractionation method, and the resulting material could be melt-spun into fibers, as the melt possessed significant thermal stability. The large extent of acetylation of hydroxyl groups that led to thermal stability also hindered the thermo-oxidative stabilization. Consequently, the melt-spinning approach was abandoned. Instead, to preserve more hydroxyl groups within the precursor material, the acetic anhydride amount used in acetylation of the softwood kraft lignin was reduced from 15 to 0.66 ml per gram lignin. As indicated by FTIR spectroscopy, the hydroxyl peak was significantly increased. In addition, the weight gain of lignin after reaction was reduced from 18% to 5%, indicating a partial acetylation of the hydroxyl groups in softwood kraft…
Subjects/Keywords acetylation; bio-based; carbon fibers; dry spinning; lignin
Contributors Dr. Amod A. Ogale, Committee Chair; Dr. Douglas Hirt; Dr. Christopher Kitchens; Dr. Rajendra Kumar Bordia
Country of Publication us
Record ID oai:tigerprints.clemson.edu:all_dissertations-2617
Repository clemson
Date Retrieved
Date Indexed 2020-05-01

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