Bound water restrained by nanocellulose fibres

The higher-order structure of natural cellulose fibres changes in the presence of water. In order to investigate the effect of molecular level fibre structure, melting behaviour of water restrained by nano- and microcellulose fibre was measured by differential scanning calorimetry. Fibre size was measured by scanning electron microscopy and atomic force microscopy. It was found that the melting peak of water restrained by microcellulose fibre started at 250-260 K in a W (c) (=mass of water/mass of dry sample) range from 0.5 to 1.2, whereas that of nanocellulose fibre was 230-237 K. Furthermore, peak temperature of melting of water restrained by nanocellulose was observed at around 270 K, in contrast, that of water restrained by microcellulose fibre was observed at ca. 275 K. Bound water content was calculated from melting enthalpy. Both non-freezing and freezing bound water of nanocellulose fibre was far larger than that of microcellulose. The above results suggest that a large amount of freezing bound water is restrained in nanocellulose fibres. It is thought that a larger number of isolated hydroxyl groups exist on the fibre surface.