Abstract
Lignin/lignin blends were used to improve fiber spinning, stabilization rates, and properties of lignin-based carbon fibers. Organosolv lignin from Alamo switchgrass (Panicum virgatum) and yellow poplar (Liriodendron tulipifera) were used as blends for making lignin-based carbon fibers. Different ratios of yellow poplar:switchgrass lignin blends were prepared (50:50, 75:25, and 85:15 w/w). Chemical composition and thermal properties of lignin samples were determined. Thermal properties of lignins were analyzed using thermogravimetric analysis and differential scanning calorimetry. Thermal analysis confirmed switchgrass and yellow poplar lignin form miscible blends, as a single glass transition was observed. Lignin fibers were produced via melt-spinning by twin-screw extrusion. Lignin fibers were thermostabilized at different rates and subsequently carbonized. Spinnability of switchgrass lignin markedly improved by blending with yellow poplar lignin. On the other hand, switchgrass lignin significantly improved thermostabilization performance of yellow poplar fibers, preventing fusion of fibers during fast stabilization and improving mechanical properties of fibers. These results suggest a route towards a 100% renewable carbon fiber with significant decrease in production time and improved mechanical performance.
Highlights
Lignin has been explored as a precursor for low-cost and bio-derived carbon fibers since the 1960s [1,2,3], but it has gained significant attention recently as many industries seek to find renewable replacements for petroleum derived carbon [4,5]
We demonstrated how thermal properties and chemical structure of organosolv hardwood and herbaceous lignins results in differences in melt-spinning, thermostabilization performance, and properties of resulting carbon fibers [3]
Yellow poplar and switchgrass lignins produce miscible blends that do not phase separate with thermal processing
Summary
Lignin has been explored as a precursor for low-cost and bio-derived carbon fibers since the 1960s [1,2,3], but it has gained significant attention recently as many industries seek to find renewable replacements for petroleum derived carbon [4,5]. Manufacturing lignin carbon fibers involves multiple processing steps of melt-spinning, oxidative thermostabilization, and carbonization. Especially organosolv, has demonstrated greater thermal mobility and better spinnability, while lignins from softwoods and grasses have better performance during thermostabilization and conversion processes [2,3,6,14,15]. Lignins with a high number of guaiacyl (G) units (softwoods and grasses) have a more condensed and cross-linked structure, which limits thermal mobility and causes difficulty in melt-spinning [2,3,15]. The more condensed structure (C–C linkages) and unoccupied C5 sites in high G content lignins (grasses and softwood) promotes faster thermostabilization and reduces carbon fiber production time [3,15]
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