Carbon Fibers Derived from Fractionated–Solvated Lignin Precursors for Enhanced Mechanical Performance

Abstract

The sustainable solvent system acetic acid + water was used to simultaneously fractionate, solvate, and clean a softwood Kraft lignin for conversion to carbon fibers. By exploiting the novel liquid− liquid equilibrium (LLE) phase behavior exhibited by this pseudoternary system, three fractionated−solvated lignin precursors (FSLPs) of increasing molecular weight (7200, 13 800, and 28 600) were obtained via the continuous Aqueous Lignin Purification using Hot Acids (ALPHA) process. It is noteworthy that all three FSLPs, isolated as the lignin-rich liquid phase, had very low metals/ash content (230 ppm of Na and 0.07 wt % ash), in contrast to that of the bulk feed lignin (1400 ppm of Na and 0.60 wt % ash). Lignin fibers were successfully spun from the FSLPs by dry-spinning. Subsequently, the lignin fibers could be rapidly stabilized and carbonized at 1000 °C to produce carbon fibers with equivalent diameters less than 7 μm. Carbon fibers obtained from the highest molecular weight FSLP possessed an average tensile strength and modulus of 1.39 and 98 GPa, respectively, representing the highest mechanical properties ever obtained for carbon fibers derived from low-cost, chemically unmodified lignin.

Valorization of Lignin as a Sustainable Component of Structural Materials and Composites: Advances from 2011 to 2019

“…Water soluble lignin-based CFs had a lower yet still practically viable elastic modulus of 16 GPa, similar to the modulus for pure kraft lignin-derived CFs (15.7 GPa). Despite using lignin as a sustainable feedstock in this process, it should be noted that all of the PAN-derived CF reactions emit toxic hydrogen cyanide gas, which is a drawback to this approach [42].…”

Wet‐Spinning and Carbonization of Lignin‐Polyvinyl Alcohol Precursor Fibers

“…In addition, PVA displays strong interactions with lignin, [19] and as shown further, can even exhibit partial miscibility with lignin. [2,6,18] In contrast to previous related investigations, we use unmodified lignin to keep the cost low, and 2-propanol as coagulating medium to keep the process simple and environmentally friendly. We demonstrate the fabrication of lignin-based fibers via a continuous wet-spinning method using nonhazardous solvents (dimethyl sulfoxide (DMSO) and 2-propanol) at room temperature.…”

“…[2,8,10] In addition, it leads to carbon fiber properties that compare or exceed the properties of fibers made from other types of lignin. [2,6,18] In contrast to previous related investigations, we use unmodified lignin to keep the cost low, and 2-propanol as coagulating medium to keep the process simple and environmentally friendly.…”

Are lignin-derived carbon fibers graphitic enough?

“…Jin et al (2018) isolated and fractionated softwood kraft lignin from black liquor using the ALPHA process, which uses liquid-liquid equilibrium present in an acetic acid-water solution. 52 This method allows for separating lignin by molecular weight through adjusting the ratio of acetic acid to water. The researchers used this feature to produce lignin-derived CFs from three samples with different molecular weights, and they found that tensile strength and modulus increase as molecular weight increases.…”