Studies on Bound Water of Cellulose by Differential Scanning Calorimetry

The crystallization and melting of adsorbed water on cellulose samples such as cotton, kapok, linen, jute, various rayons, and wood cellulose have been studied using a differential scanning calorimeter (DSC). Two exothermic peaks of crystallization of adsorbed water on the cellulose samples are observed. One is a sharp peak (Peak I) observed at about 255 K in a DSC curve; the other is a broad peak (Peak II) observed at about 230-250 K. Judging from the amounts of water calculated from the results obtained by the DSC study, there seems to be some nonfreezing water which does not crystallize. Therefore, we have categorized water adsorbed on cellulose samples as one of three different kinds: free water (Peak I), freezing bound water (Peak II), and nonfreezing bound water. The bound water content is dependent on the degree of crystallinity of cellulose samples. The amounts of bound water estimated are from 1.0 to 2.2 moles per one glucose unit of cellulose. However, the amount of water bound to each glucose unit was 3.4 moles, if we took into consideration that water diffuses only into the amorphous region of each cellulose sample.