DEVELOPING A MOLECULAR DESCRIPTION OF ADSORPTION AND SOLUBILITY OF CELLULOSE

Abstract

Cellulose is a promising sustainable and biorenewable feedstock with a range of applications, from bulk commodities to plastics and biofuels. However, the poor solubility of cellulose in conventional solvents limits the widespread application of cellulosic material. Despite the persistence of the problem, the physical cause of the insolubility of cellulose is yet to be fully understood.

The overarching aim of this thesis is to apply molecular simulation methods to quantify the stability of a comprehensive range of cellulose-solvent interfaces towards providing insight into the dissolution of native cellulose. Molecular simulation methods are applied to calculate the stability, and hence native abundance, of selected low Miller index crystalline surfaces of I cellulose. A combination of rst-principle and potential-based methods are also applied to determine the most stable morphology of cellulose microbrils. Finally, potential-based methods are applied to investigate the thermodynamic stability of cellulose-solvent interfaces.

The results predict that the surfaces of cellulose undergo signicant surface relaxation in order to increase the stability of the surface. Isolated surfaces of crystalline cellulose will rearrange to resemble the stable {100} surface. Moreover, square microbrils of native cellulose will rearrange to adopt more stable pseudo-hexagonal morphologies. The stability of such dry cellulose surfaces is driven primarily by the van der Waals interactions. When considering cellulose-water interfaces, the work of adhesion is the most appropriate measure of stability. The nature of the cellulose surface is fundamental to the stability of cellulose-water interfaces. Decomposing the inter-molecular interactions that contribute to these cellulose-water works of adhesion reveals that Coulombic interactions drive the strong binding of water to cellulose. Finally, the binding of imidazolium-based ionic liquids to cellulose also varies between surfaces and is also dominated by the Coulombic interactions between cellulose and the
chloride anion. However, the anion and cation form closely associated ion pairs as well as secondary clusters of ions. The close association of the ions results in a destabilising interaction between the cations and cellulose which may result in the disruption of the crystalline lattice of cellulose, ultimately leading to dissolution.

Date of Award	10 Sept 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	Steve Parker (Supervisor), Janet Scott (Supervisor), Robert Grant (Supervisor) & Tina Düren (Supervisor)