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Dissertation - University Access Only
Doctor of Philosophy (PhD)
Chemistry and Biochemistry
Douglas E. Raynie
Lignin is an aromatic polymer, formed by polymerization of p-hydroxyphenyl (H), guaiacyl (G), and sinapyl (S) moieties through ether and carbon-carbon linkages. Lignin is highly produced as waste and understanding structural characteristics of lignin will increase its utilization. Prairie cordgrass lignin (PCGL), switchgrass lignin (SGL), big bluestem lignin (BBSL), and miscanthus lignin (MSL) were isolated by an organosolv method with 90% extraction yields. Differential scanning calorimetry analysis show SGL had the highest glass transition temperature at 50.5ºC, PCGL had the highest melting temperature at 70.4ºC, and PCGL and SGL had the highest crystallization temperature at 57.8 and 56.9ºC. Thermogravimetric analysis show that mass loss of lignin was achieved primarily in three stages and temperatures between 250 to 350ºC break the β-0-4 linkage, which is the major interunit linkage present in lignin. In addition, PCGL and SGL have high thermal transition temperatures and lower decomposition compared to BBSL and MSL. Nitrobenzene and cupric oxide oxidation results demonstrate vanillin and syringaldehyde as the major phenolic moieties. Pyrolysis-gas chromatography-mass spectrometry identified 4-vinylguaiacol, phenol, guaiacol, 2-methoxy-4-methyl phenol, eugenol, syringaldehyde, and acetosyrinzone as major phenolic moieties. 1H NMR spectroscopy analysis demonstrates that the amount of formyl group, phenolic hydroxyl group, aromatic proton, β-5 unit, aliphatic hydroxyl, β-1 unit, and β-β units are comparatively similar in PCGL, SGL, BBSL, and MSL. However, variations in the amount of carboxylic and β-O-4 linkages were observed. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry results identified monomers from H, G, and S families and polymerization in PCGL and SGL up to seven units and BBSL and MSL up to eight units. The observed mass pattern in PCGL is comparable to SGL and BBSL is comparable to MSL. Direct-polarization magic-angle-spinning (DP MAS) 13C-NMR spectroscopy analysis showed the oxygenated aromatic and the aromatic carbon-carbon regions are quite similar in PCGL, SGL, and BBSL and are low compared to MSL, whereas the aromatic methine carbon region is richer in PCGL. Among the selected lignins, PCGL and SGL have higher degrees of condensation compared to BBSL and MSL. Although, the selected grass lignins primarily constitute similar structural moieties and inter-unit linkages, they widely wary in the amount present. In summary, PCGL and SGL showed higher thermal stability and similar structural patterns among the selected grass lignins, which is supported by higher condensation resulting in stronger bonds between phenolic moieties and similar mass patterns.
Library of Congress Subject Headings
Includes bibliographical references (pages 116-124)
Number of Pages
South Dakota State University
In Copyright - Educational Use Permitted
Bathula, Vinod, "Comprehensive Structural and Thermal Characterization of Selected Grass Lignins" (2013). Electronic Theses and Dissertations. 1368.