Abstract
Cellulose–lignin composite carbon fibers have shown to be a potential environmentally benign alternative to the traditional polyacrylonitrile precursor. With the associated cost reduction, cellulose–lignin carbon fibers are an attractive light-weight material for, e.g. wind power and automobile manufacturing. The carbon fiber tenacity, tensile modulus and creep resistance is in part determined by the carbon content and the molecular orientation distribution of the precursor. This work disassociates the molecular orientation of different components in cellulose–lignin composite fibers using rotor-synchronized solid-state nuclear magnetic resonance spectroscopy and X-ray scattering. Our results show that lignin is completely disordered, in a mechanically stretched cellulose–lignin composite fiber, while the cellulose is ordered. In contrast, the native spruce wood raw material displays both oriented lignin and cellulose. The current processes for fabricating a cellulose–lignin composite fiber cannot regain the oriented lignin as observed from the native wood.
Highlights
There is currently a growing aspiration of producing inexpensive carbon fibers, mainly to achieve a suitable light-weight material for the automotive and wind power industry (Mainka et al, 2015)
A bundle of composite cellulose–lignin fibers was spun on a flat spool with a thin layer of polystyrene glue applied between wounds
With a combination of ROSMAS NMR spectroscopy and WAXS, disassociation of molecular orientation in a cellulose–lignin composite
Summary
There is currently a growing aspiration of producing inexpensive carbon fibers, mainly to achieve a suitable light-weight material for the automotive and wind power industry (Mainka et al, 2015). Previous studies have reported lignin-based carbon fibers produced with wet-, dry-, and melt-spinning (Baker & Rials, 2013; Bengtsson et al, 2018; Zhang & Ogale, 2014). Follmer et al (2019) presented a study with the ambition to induce a preferred orientation in lignin by adding graphene oxide to the spinning dope solution They found an increased orientation with graphene oxide concentration, though they could not distinguish if lignin contributed to the anisotropy, neither could the combination of lignin and graphene oxide be used to produce continuous fibers. The ability to perform continuous spinning and the application of a draw ratio higher than 1 are essential features to achieve high molecular orientation of a regenerated cellulose fiber (Michud, Hummel, & Sixta, 2016). Is lignin, which is chemically bound to oriented hemicellulose or cellulose, acting as scaffold? Is it possible to induce any molecular orientation preference to the lignin molecules in synthetic conditions? These are both questions that concern the work
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