Abstract
Production of high strength carbon fibers from bio-derived precursors is of topical interest. Recently, we reported on dry-spinning of a partially acetylated softwood kraft lignin to produce carbon fibers with superior properties, but the thermo-oxidative stabilization step required a long time due to a slow heating rate needed to prevent the fibers from being heated too rapidly and sticking to each other. Here we report a rapid strategy of dual UV-thermoxidative stabilization (crosslinking) of dry-spun lignin fibers that significantly reduces the stabilization time. The fibers undergo reaction close to the surface such that they can be subsequently thermally stabilized at a rapid heating rate without fibers fusing together, which reduces the total stabilization time significantly from 40 to 4 h. Consequently, the glass transition temperature of UV irradiated fibers was about 15 °C higher than that of fibers without UV treatment. Stabilized fibers were successfully carbonized at 1000 °C and resulting carbon fibers displayed a tensile strength of 900 ± 100 MPa, which is amongst the highest reported for carbon fibers derived from softwood lignin-based precursors. These results establish that UV irradiation is a rapid step that can effectively shorten the total stabilization time for production of lignin-derived carbon fibers.
Highlights
IntroductionPrecursor fibers that are obtained by a wet-spinning process [1,2,3]
The vast majority of commercial carbon fibers are currently produced from polyacrylonitrile (PAN)precursor fibers that are obtained by a wet-spinning process [1,2,3]
The Ace-Softwood kraft lignin (SKL) coated KBr pellets were irradiated in the UV chamber for 3, 10, 15, 20, and 25 min total exposure time
Summary
Precursor fibers that are obtained by a wet-spinning process [1,2,3]. Hydrogen cyanide) are generated, and the wet-spinning process involves the use of hazardous solvents [1,2,3]. Lignin is regarded as a potential carbon fiber precursor due to its low cost and high aromatic content. Different types of lignin precursors have been explored to produce carbon fibers, and most of these studies involved melt-spinning of a fusible lignin, which possessed a low enough softening temperature [4,5,6,7,8,9,10]. The normally low glass transition temperatures (Tg) of such lignin precursors required a slow heating rate to achieve crosslinking without fibers becoming tacky. According to Braun’s analysis for continuous heating transformation [4], heating rate during thermal stabilization needs to be below
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