VALUE-ADDED LIGNIN BASED CARBON FIBER FROM ORGANOSOLV FRACTIONATION OF POPLAR AND SWITCHGRASS

Carbon fibers have unique properties that include high strength, low density and excellent chemical and thermal resistance. However, they have a low level of utilization because of their high price; typically around $30/kg for an entry level polyacrylonitrile (PAN) based carbon fiber. Low-cost carbon fibers derived from lignin are currently being investigated at the University of Tennessee, because using lignin as a precursor could significantly reduce production costs. Lignins obtained from the pulp and paper and the emerging biofuel industries have the potential to be used for carbon fiber production, however, they are typically unsuitable because of the high levels of impurity and variable thermal properties. This research study examines the potential of a novel organosolv process to provide high purity lignin for carbon fiber production. This fractionation separates woody and herbaceous bioenergy crops into their three main components: cellulose, hemicellulose, and lignin, each of which can be used within the biorefinery for the production of fuels or chemicals. In this program, organosolv derived lignin from both tulip poplar (Liriodendron tulipifera) and Alamo switchgrass (Panicum virgatum) were recovered and compared as starting materials for carbon fiber. The organosolv derived lignin was analyzed using several different methods to assess quality differences for potential carbon fiber manufacture. Their purities, chemical structures, consistencies, thermal, and carbonization properties were evaluated and lignin exhibiting optimal properties was used for fiber spinning and conversion to carbon fiber. Lignin exhibiting the best thermal performance was achieved by isolation at 150°C to 170°C with an acid concentration of 0.05 and 0.1 M H₂SO₄, and a fractionation time of 120 and 180 minutes. Organosolv fractionation conditions and their influence on the properties of lignin-based carbon fiber are presented in this thesis.