Natural deep eutectic solvents (NADES) based on citric acid and sucrose as a potential green technology: a comprehensive study of water inclusion and its effect on thermal, physical and rheological properties

In this work, NADES based on sucrose and citric acid was synthesised and evaluated. Physical properties such as density, viscosity and thermal profile were evaluated at different temperatures and water contents. Viscosity and density were inversely affected by temperature and water content. Increases in the sucrose fraction resulted in higher viscosity, but no differences in density were observed. The rheological model of Ostwald-de-Waele indicated three distinct rheological behaviours at different temperatures, water content and sucrose fractions. The Arrhenius model showed a good fit for the temperature effect on the apparent viscosity of all NADESs. The NADES decomposition temperature was approximately 393 K. The thermal characterisation revealed that all NADESs presented glass transitions at temperatures below 204.59 K, confirming their formation and stability. Based on these results, the NADES proposed appears as potential green solvent to be used in industrial processes such as extraction, separation and biochemical technology.