Solid structure of native celluloses from different origins and their solubility in LiCl/amide systems

Native celluloses from different origins show variant solubility in lithium chloride/amide solvent system. The solubility of some of native cellulose is enhanced by solvent exchange procedure, namely sequential immersion in water, acetone, and amide solvents. In order to investigate the effect of the solvent exchange on the solubility and the solid structure of native celluloses, small angle X-ray scattering (SAXS), cross-polarized/magic angle spinning (CP/MAS) ¹³C solid-state NMR, and X-ray photoelectron spectroscopy (XPS) measurements were performed. It was revealed from SAXS and solid-state NMR that the solvent exchange significantly affects the submicron-scale solid structure of wood and cotton celluloses. On the other hand, that of microbial and tunicate celluloses is less affected by the solvent exchange. The structural change induced by the solvent exchange is relevant to the enhancement of the solubility, which is supported by the fact that the XPS detected a vestige of dimethylacetamide (DMAc) molecules strongly absorbed on the surface of the cellulose sample even under an extreme vacuum condition.