Carbon Fibers from Lignin–Cellulose Precursors: Effect of Carbonization Conditions

Abstract

Carbon fibers (CFs) are gaining increasing importance in lightweight composites, but their high price and reliance on fossil-based raw materials stress the need for renewable and cost-efficient alternatives. Kraft lignin and cellulose are renewable macromolecules available in high quantities, making them interesting candidates for CF production. Dry-jet wet spun precursor fibers (PFs) from a 70/30 w/w blend of softwood kraft lignin (SKL) and fully bleached softwood kraft pulp (KP) were converted into CFs under fixation. The focus was to investigate the effect of carbonization temperature and time on the CF structure and properties. Reducing the carbonization time from 708 to 24 min had no significant impact on the tensile properties. Increasing the carbonization temperature from 600 to 800 °C resulted in a large increase in the carbon content and tensile properties, suggesting that this is a critical region during carbonization of SKL:KP PFs. The highest Young’s modulus (77 GPa) was obtained after carbonization at 1600 °C, explained by the gradual transition from amorphous to nanocrystalline graphite observed by Raman spectroscopy. On the other hand, the highest tensile strength (1050 MPa) was achieved at 1000 °C, a decrease being observed thereafter, which may be explained by an increase in radial heterogeneity.

Improved Procedure for Electro-Spinning and Carbonisation of Neat Solvent-Fractionated Softwood Kraft Lignin

“…The increase in the ratio of I D /I G is directly in contrast to carbon bres made from PAN where this ratio is seen to decline with the increasing carbonisation temperature [56][57][58] . However, these ndings are in complete agreement with reported Raman results on the carbon bres obtained from lignin 4,20 . Moreover, it is reported that the higher molecular weight of lignin enhances the graphitic structure and mechanical performance 59 .…”

“…This band is a result of second order resonance from the D-band and it is normally referred to as 2D band. This 2D band is a characteristic feature of increased stacking in the layered graphitic sheets 4,54 .…”

“…It is seen in Table 3 that the D and G-bands experience a decrease in the FWHM values, but G-band shows more narrower line width as the carbonisation temperature is increased. This indicates the lignin sample carbonised at higher temperature start to attain a crystallite graphitic structure 4,60 .…”

“…Over the past decade, the use of naturally occurring biomaterials such as lignin and cellulose as an alternative precursor to polyacrylonitrile (PAN) for the production of carbon bres has been studied extensively. [1][2][3][4][5] PAN continues to be the primary precursor for the production of carbon bres. However, PAN is derived from petroleum and it is not a sustainable precursor in the long-term 6,7 .…”

The challenge of predicting spinnability: Investigating benefits of adding lignin to cellulose solutions in air‐gap spinning

“…Thus, less expensive, and preferably bio‐based raw materials for carbon fibers are sought for. Recent research has shown great promise in carbon fibers produced from a combination of lignin and cellulose 7,8 . The advantage of using lignin and cellulose is that they are both bio‐based and abundant materials, thus enabling a less expensive carbon fiber 9 .…”