Solute adsorption and exclusion studies of the structure of never-dried and re-wetted cellulosic fibres

The total water capacity of a series of never-dried and re-wetted cellulosic fibres has been shown to correlate with the accessible volume described by a thermodynamic model. The model was applied to interpret the adsorption behaviour of a range of reactive dyes in electrolyte solutions and was successful in accounting for differences in fibre anionic charge. Comparative solute exclusion data indicated the existence of a population of very small spaces in never-dried cellulosic fibres, which may be associated with water disrupting the cellulose 1 (1) over bar0 crystal planes. Such intra-crystalline spaces may provide sites for uptake of planar substantive dyes and may also be accessible to sodium ions. The study showed that never-dried lyocell undergoes a large reduction in total wet capacity following initial drying, which is believed to be due to both exudation of crystal water and to inter-fibrillar crystallisation. This crystallisation mechanism may not be so effective for viscose and modal, which have poorer structural organization. Re-wetted lyocell exhibits high dye adsorption, which may result from the development of a uniform fibrillar morphology with a high surface area. This structural aspect is not expressed by the thermodynamic model.