Mechanism of cellulose gelation from aqueous alkali-urea solution.

Molecular process of regeneration-gelation of cellulose from aqueous alkali-urea solvent was monitored by synchrotron-radiation X-ray. The wide-angle diffraction from cellulose during regeneration, both by coagulant and heating, gave information on behavior of cellulose molecules, i.e. the glucopyranoside rings first stack by hydrophobic interaction to form monomolecular sheets, which then line up by hydrogen bonding to form Na-cellulose IV type crystallites (hydrate form of cellulose II). While such a process in regeneration of cellulose has been hypothesized and supported by molecular dynamics or monitoring of mercerization process, our observation finally confirmed it experimentally. This knowledge will be useful in understanding behavior of cellulose molecules during regeneration, leading to better controls of resulting structure and properties.