Isothermal ternary phase diagram of the polylactic acid-dichloromethane-hexane system

Abstract

The ternary phase diagram of polylactic acid, dichloromethane (solvent) and hexane (nonsolvent) is experimentally developed at room conditions based on naked eye observations over 14-day periods. The experimental procedure is explained in detail, allowing it to be applied to similar ternary systems. Three regions are distinguishable in this diagram: single phase, liquid–liquid phase separated and solid–liquid phase separated. This diagram is then assessed based on the lever rule concept in ternary phase diagrams. Phase separation kinetics are also evaluated using turbidity studies to quantitatively monitor the cloudiness of the samples over time. The results show that, a small increase in polylactic acid concentration on the order of a few weight percent can drastically increase the phase separation rate. The application of polylactic acid in various fields has been increasing, and this work provides fundamental information essential for solvent-based processing (e.g., nonsolvent induced phase separation and immersion-precipitation) of this polymer in the system composed of dichloromethane and hexane.