POLYSACCHARIDE SOLUTIONS FROM A STATISTICAL THERMODYNAMIC PERSPECTIVE AND THE DEVELOPMENT OF CELLULOSE ANALOGUES

The development of new cellulose solvents, motivated by environmental concerns, would greatly benefit from a full understanding of the cellulose dissolution mechanism. With a focus on aqueous solvents, this thesis made progress towards understanding the molecular interactions in solution that lead to successful dissolution of cellulose. These molecular interactions were quantified by using statistical thermodynamic theory based on the Kirkwood-Buff (KB) theory of solutions. This was applied to cellobiose and gave insights into the interactions present in its solubility, highlighting the importance of preferential salt-cellobiose interaction and lending support to the hypothesis of “cellulose charging up” seen in the literature. However, extension of this theory for application to cellulose requires improvement in both accuracy and reliability of solubility quantification. An experimental investigation identified the problem of incomplete dissolution below the saturation point, which is responsible for major inaccuracies in solubility measurements of amorphous cellulose. The requirements for an analogue of cellulose and the correct choice of measurement protocol for solubility of cellulose were identified.
In addition to molecular level interactions, macroscopic scale phenomena such as gelation and precipitation could be seen as equally important for understanding cellulose behaviour in solvents. Design of new methods of analysis is required to understand these phenomena in a manner beyond the capabilities of traditional polymer theory. Hence an extension of KB theory using starch gelatinisation as a basis was developed. When applied to starch gelatinisation, this theory clarified the mechanism behind the effect of salt concentration on temperature dependence of gelatinisation. (Salts are excluded from gelatinised starch at low salt concentrations and anions can access inside the starch granule at higher concentration.) Similar theory could be applied to cellulose gelation, or precipitation, to glean information about the interactions present in their mechanisms.