The dissolution mechanism of crystalline cellulose in precooled aqueous NaOH/Urea solution was studied using molecular dynamics (MD) simulations. We found that hydroxide ions, sodium ions and urea all enter the first solvation shell of individual cellulose chains and thus directly interact with cellulose. In classical MD simulations, the hydroxide and sodium ions form strong, long-lasting (&gt; 100 ns) bonds with the hydroxyl groups, whereas the urea-cellulose interactions were much weaker. By constructing a small simulation box containing cellobiose(or cellotriose), NaOH, urea and water, we performed <i>ab initio</i> MD simulation and found the strong, long-last hydrogen bonds between hydroxide ions and hydroxyl groups of cellulose resulted in the partial depotonation of cellulose chain, and subsequently leaded to the production of Na-cellulose complex. This suggested that cellulose chain was partially derivate during dissolution process, which might favor the dissolution, as cellulose derivatives are more readily dissolved than cellulose itself. Meanwhile, the presence of urea in the first solvation shell did not reduce the total number of water molecules surrounding cellulose, but instead expelled water from the axis of the pyranose ring, thereby changing the orientation of the water molecules. Thus, the change in entropy induced by urea plays an essential role in the dissolution process. In summary, this study confirms formation of Na-cellulose complexes as an important intermediate step during cellulose dissolution in alkaline solution and suggests cellulose dissolution in alkaline solution is not a fully physical process. A similar picture can be applied to cellulose dissolution in other solvents, such as ionic liquids, which are known to react with and even partially degrade cellulose chains.

Na-cellulose complex dominates the dissolution of crystalline cellulose in precooled aqueous NaOH/Urea solution

251st National Meeting (2016)

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