(453f) Polymer–Solvent Phase Behavior of Lignin with Hot Aqueous Solvent Systems
Determining the temperature at which the ligninâsolvent mixture undergoes the phase transition from solidâliquid equilibrium to liquidâliquid equilibrium can be difficult, as visual observation is impeded by the opalescence of the system. Thus, a detection method based on electrochemical impedance spectroscopy (EIS) has been developed and was used to locate SLE to LLE phase boundaries for two lignin polymerâsolvent systems over a range of organic/water solvent ratios. We expect that this EIS method can be applied to other polymerâsolvent systems when standard techniques such as differential scanning calorimetry (DSC) fail.
Liquidâliquid equilibrium (LLE) phase behavior has been measured for the acetic acidâwaterâlignin system at 70 and 95 Â°C, with the results being presented as ternary phase diagrams depicting all regions of both fluid and solid phase behaviour. Measurements for at least one other ligninâsolventâwater system will also be presented. A number of important thermodynamic properties relevant to the processing of lignin can be obtained from these diagrams, including the degree of solvation in the lignin (polymer)-rich phase as a function of solvent composition, the size of the LLE region available for polymer processing, and the distribution of lignin between the polymer-rich and solvent-rich phases. Our ability to both control and model the size of the LLE region will also be discussed, along with the implications of the observed polymerâsolvent phase behavior for the development of a viable purification and fractionation process for raw, unpurified lignins.