Disassociated molecular orientation distributions of a composite cellulose-lignin carbon fiber precursor: A study by rotor synchronized NMR spectroscopy and X-ray scattering

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.

Keywords: Carbon fibers; Composite; Fiber; Lignin; Molecular orientation distribution; Regenerated cellulose; Rotor synchronized magic-angle spinning; Solid-state NMR; Wood; X-ray scattering.