Carbon fibers (CFs) possess outstanding specific strength and modulus. Therefore, they are used commercially in structural composite applications (viz. aerospace) for enhanced performance and fuel efficiency, resulting from superior strength-to-weight ratio. The vast majority of commercial CFs are currently produced from a synthetic precursor polyacrylonitrile (PAN) via wet-spinning. The cost of PAN precursor not only contributes to about 50% of CF costs, but the nitrile groups generate toxic by-products (viz. hydrogen cyanide) during heat-treatment. Thus, bio-derived CF precursors are of increasing interest from an environmental perspective. Among renewable feedstocks, lignin is an important potential precursor for carbon fibers [1,2]
. Although lignin is readily available as an inexpensive by-product, it is too high in metal impurities. Therefore, a renewable solvent system consisting of hot-acetic acid-water mixture has been developed to purify, fractionate, and solvate kraft lignins [3,4]
. Using different molecular weight fractions of the solvated lignin, direct dry-spinning of lignin precursor fibers was accomplished, followed by their conversion to carbon fibers. The resulting CFs possessed a tensile strength of 1.3±0.3 GPa and modulus of 86±8.8 GPa, and represents the highest combination of strength and modulus of CFs derived from lignin.
1. Zhang, M.; Ogale, A. A. Carbon fibers from dry-spinning of acetylated softwood kraft lignin. Carbon. 2014, 69, 626-629.
2. Ogale, A. A.; Zhang, M.; Jin, J. Recent advances in carbon fibers derived from biobased precursors. J. Appl. Polym. Sci. 2016, 133 (45).
3. Klett, A. S.; Chappell, P. V.; Thies, M. C. Recovering ultraclean lignins of controlled molecular weight from Kraft black-liquor lignins. Chem. Comm. 2015, 51, 12855-12858.
4. Klett, A. S.; Payne, A. M.; Thies, M. C. Continuous-Flow Process for the Purification and Fractionation of Alkali and Organosolv Lignins. ACS Sustainable Chem. Eng., 2016, 4, 6689-6694.