High performance electrospun carbon nanofiber mats derived from flax lignin

Abstract

Flax (Linum usitatissimum) is an abundant source of natural fiber that is industrially cultivated globally for the production of linen as well as for linseed oil. Flax shives isolated from these operations represent a significant source of underutilized biomass. This study reports a novel method to delignify flax shives, describes the characteristics of the isolated flax lignin, and the properties of carbonized fiber derived from the lignin. Knife-milled flax straw was pretreated using a glycerol thermal process that permitted the fractionation of lignin via solvent extraction. The resulting lignin was characterized for its thermal properties, chemical structure, and molecular weight using differential scanning calorimetry, 31P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and gel permeation chromatography. Additionally, the isolated lignin was transformed into continuous nanofiber mats by electrospinning, using blends of lignin and differing concentrations of polyethylene oxide (PEO). The addition of PEO as a co-processing polymer facilitated the production of uniform nanofibers without defects, such as beading. As-spun nanofiber mats were thermally stabilized in an oxygen environment and subsequently carbonized at 1000 °C. The ensuing nanofiber mats had similar mechanical properties to carbon nanofiber mats spun from softwood kraft lignin, and outperformed those derived from organosolv processed hardwoods.