The interaction between water and cellulose is of utmost importance in order to understand and control the properties of cellulosic materials. Although the topic has been studied extensively there is still no consensus regarding all aspects related to moisture interaction with different hydroxyl groups of the cellulose and how ultrastructural changes of the cellulose may affect these interactions. To a large extent this relates to the complex structure of the cellulose itself with only partly crystalline microfibrils surrounded by, more or less, unordered molecules. The fact that these microfibrils may further aggregate into larger units of a broad range of sizes further complicates the structural interpretations. The crystalline parts of the cellulose are not accessible by moisture and it has also been advocated that the areas in-between microfibrils in the aggregates would also be inaccessible. Measurements of moisture mobility by FTIR and NMR indicate however that there are two different types of sorbed, bound water in the relative humidity, RH, range; one type exhibiting restricted motion and another type representing a more mobile bound water. Examining the behaviour of these types of water suggests that the less mobile water could be associated to surfaces in-between microfibrils while the more mobile water would be associated to the microfibril surfaces facing outwards from the aggregates, i.e. areas of easier access. In processing of cellulosic fibres, like pulping and drying, substantial changes in both aggregate size, porosity and water holding capacity takes place. These changes, associated with aggregation/de-aggregation of the microfibrils, will affect the moisture sorption ability and the accessibility of hydroxyls as well as the water holding capacity. These issues will be further delved upon.

Accessibility of hydroxyl groups related to cellulose aggregation

255th National Meeting (2018)

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