Automated trackspinning of highly oriented, ultrafine lignin fibers as precursors for green carbon nanofibers

At present, most carbon fibers are made from non-renewable polyacrylonitrile (PAN). Substantial efforts have been made to replace the need for petroleum-based precursors for carbon fiber production. Interestingly, lignin is a carbon fiber precursor material that is cheap, highly available, and sustainable. Sub-micron scale lignin-based carbon nanofibers could find use in numerous areas, such as electronic devices, batteries, supercapacitors, and low-cost, high performance structural composite materials. Trackspinning (TS) technology offers a way scale the versatile, but inefficient mechanical pulling technique to produce small diameter lignin fibers from environmentally friendly aqueous solutions. In this study, the effects of track spinning based on probe drawing of low concentration lignin nanofibers blended with polyethylene oxide (PEO) and glycerol in sodium hydroxide (NaOH) solution were investigated. TS lignin fibers were well aligned and reached diameters as low as 500-1000 nm as the drawing length was increased. Lignin fiber macromolecular alignment was isotropic at low levels of draw and dichroic ratio was increased from 1 to 2.25 by doubling the drawing length. The most highly drawn track-spun lignin fibers had a mechanical strength of 3.92 MPa and a Young’s Modulus of 2.15 GPa, which were similar to reported values for solvent electrospun lignin nanofibers. These findings support the potential to utilize TS to produce small diameter lignin fibers using a simple aqueous solvent approach.