Deep Eutectic Solvents Derived From Inorganic Salts

Mixtures of metal salts with complexing agents, such as urea, form liquids, which are known as deep eutectic solvents (DESs). This has previously been applied to metal salts such as ZnCl₂, AlCl₃ and CrCl₃.6H₂O. The aim of this thesis was to see if this model could be expanded to include alkali metal salts. Some of the hydrogen bond donors (HBDs) investigated were found to form liquid mixtures with a limited number of alkali metal salts, which showed melting temperatures below 25 °C. Utilising glycerol as a HBD exhibited the highest mutual solubility with the alkali metal salts of interest, therefore this study focussed on sodium salt:glycerol mixtures. Four sodium salts were chosen: NaBr, NaOAc, NaOAc.3H₂O or Na₂B₄O₇.10H₂O, which provided a range of fluidities and contained hydrates and anhydrous salts. The ionic conductivity and viscosity of these salts with glycerol were studied, and it was found that unlike previous studies of choline chloride with glycerol where the salt decreases the viscosity of glycerol, all of the sodium salts increased the viscosity of glycerol. This suggests that sodium salts have a structure making, kosmotropic effect, rather than structure breaking, chaotropic effect, on glycerol. This phenomenon is probably due to the high charge density of Na⁺, which coordinates to the glycerol. The ion transport properties and molecular dynamics of sodium salt:glycerol mixtures have been investigated at the microscopic level using nuclear magnetic resonance and electrochemical techniques. Self-diffusion coefficients of the components of the systems of interest were found to be 10⁻¹¹- 10⁻¹³ m² s⁻¹ range. T₁ relaxation times were investigated and all systems showed a transition from a diffusion-limited, slow molecular tumbling regime to a fast molecular, high mobility, tumbling regime. Poor solubility was experienced with a range of transition metal salt probes, which was attributed to complex ion speciation. It was concluded that the sodium salt:glycerol systems studied are not ideal for electrochemical applications. The ability of the salts to form viscous gels made them ideal plasticisers for starch. Starch DES mixtures were tested as a binder for medium density fibreboard (MDF). The properties of MDF samples were tested as a function of processing conditions and composition. Pilot scale production of plasticised starch MDF composites was successful, demonstrating the current industrial infrastructure can be utilised for large-scale production at a similar cost to MDF bound with urea formaldehyde resins.