More Elongated Solution Structures in Lignin Precursors Improve Properties of Resultant Carbon Fibers

Kraft lignin was isolated into fractions encompassing a range of molecular weights (MW) using a fractionation/purification process. Small angle neutron scattering (SANS) was used to determine the absolute MW, molecular structure, and association behavior of these fractions in deuterated alkaline solutions. Lignin subunits are elongated, rigid, rod-like structures and exist as large aggregates. Significant elongation in lignin macromolecular dimension was observed with increasing MW, with this increasing elongation translating directly into higher-performance carbon fibers. Thus, by using SANS, the molecular structure of the precursor lignin polymer can be directly related to the properties of the final carbon fibers.