Synthesis and Physical and Thermodynamic Properties of Lactic Acid and Malic Acid-Based Natural Deep Eutectic Solvents

The research leading to these results has received funding provided by Fundacio para a Ciencia e a Tecnologia through the project PTDC/BBB-EBB/1676/2014-DesZyme. Funding from the European Union, Horizon 2020 program has also been granted through project Des.solve (ERC consolidator) ERC-2016-COG 725034. This work was supported by the Associate Laboratory for Green Chemistry, LAQV, which is financed by national funds from FCT/MCTES (UID/QUI/50006/2013) and cofinanced by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007265).In this paper, four natural deep eutectic solvents (NADES) systems were prepared at specific molar ratios, La:Bet (2:1) (lactic acid/betaine), La:Hist (9:1) (lactic acid/histidine), Ma:Bet:H2O (1:2:3) (malic acid/betaine/water) and Ma:Bet:Pro:H2O (1:1:1:2) (malic acid/betaine/proline/water). Their physical and thermodynamic properties were studied, namely viscosity, electrical conductivity, and heat capacity. The viscosity and electrical conductivity were determined as a function of temperature and the correlation for the temperature dependence was obtained and discussed based on Arrhenius theory. The heat capacity for all eutectic systems was measured by differential scanning calorimetry (DSC) over a temperature range of 293.15-363.15 K. The ability of these NADES to reduce cellulose crystallinity was evaluated. Cellulose crystallinity after suspension in these NADES was studied by X-ray diffraction. Cellulose suspended in Ma/Bet/H2O (1:2:3) suffer the highest crystallinity reduction among the systems studied and was about of 20%.authorsversionpublishe