Abstract
We introduce an eco-friendly process to dramatically simplify carbon microfiber fabrication from biobased materials. The microfibers are first produced by wet-spinning in aqueous calcium chloride solution, which provides rapid coagulation of the hydrogel precursors comprising wood-derived lignin and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF). The thermomechanical performance of the obtained lignin/TOCNF filaments is investigated as a function of cellulose nanofibril orientation (wide angle X-ray scattering (WAXS)), morphology (scanning electron microscopy (SEM)), and density. Following direct carbonization of the filaments at 900 °C, carbon microfibers (CMFs) are obtained with remarkably high yield, up to 41%, at lignin loadings of 70 wt % in the precursor microfibers (compared to 23% yield for those produced in the absence of lignin). Without any thermal stabilization or graphitization steps, the morphology, strength, and flexibility of the CMFs are retained to a large degree compared to those of the respective precursors. The electrical conductivity of the CMFs reach values as high as 103 S cm–1, making them suitable for microelectrodes, fiber-shaped supercapacitors, and wearable electronics. Overall, the cellulose nanofibrils act as structural elements for fast, inexpensive, and environmentally sound wet-spinning while lignin endows CMFs with high carbon yield and electrical conductivity.
Highlights
The demand of carbon fibers (CFs) is increasing annually at a 10% rate and is expected to reach 89 000 tons by 2020.1 This demand has been met by the supply of petroleum-based precursors, such as polyacrylonitrile (PAN) and mesoporous pitch, which make about 90% of the market.[2]
We propose for the first-time wet spinning of lignin and cellulose from aqueous suspensions to produce composite filaments and upon carbonization, the respective carbon microfibers (CMFs), with no need for melting nor dissolution
We introduce wet spinning of the bicomponent system using an aqueous coagulation bath containing dissolved CaCl2
Summary
The demand of carbon fibers (CFs) is increasing annually at a 10% rate and is expected to reach 89 000 tons by 2020.1 This demand has been met by the supply of petroleum-based precursors, such as polyacrylonitrile (PAN) and mesoporous pitch, which make about 90% of the market.[2]. The theoretical carbon content of cellulose is 44.4%, but the actual processing carbon yield is 60%), lignin is considered as a promising precursor for CFs.[15−17] In practice, lignin-based precursors have been made from two types of dopes. The other one is lignin mixed with synthetic polymers such as acrylonitrile,[19] poly(ethylene oxide),[20] polypropylene,[17] poly(ethylene terephthalate),[17] or poly(vinyl alcohol) (PVA),[2,21,22]
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