The hygroscopic power of amorphous cellulose: a modeling study

The relationship between cellulose and water was studied by building dense amorphous cellulose models and subjecting them to increasing moisture contents. When starting from completely dry cellulose, the first diffused water molecules were essentially individualized and hydrogen bonded exclusively to the O6 and O2 hydroxyl groups of cellulose. Upon continued hydration increase, the hydroxyl at O3 and then the acetal oxygens of cellulose also started to attract the upcoming water molecules, which were no longer isolated. They progressively became aggregated, first into clusters and then at high hydration content, into continuous capillary channels. A benefit of this study was to allow predicting a number of physical parameters of amorphous cellulose and their variation under hydration. With some parameters, the calculated values matched rather well the experimental literature determinations. This was the case for the hydration dependence of Tg, the stereoselectivity of the cellulose oxygen atoms for water molecules, together with the diffusion coefficients of water into cellulose. An estimate of the hygro-expansion of amorphous cellulose was provided.