Phase separation of polymer blends in solution: A case study

The phase behavior and phase separation features of the quaternary system poly-l-lactide (PLLA)/poly-rac-lactide (PLA)/dioxane/water were investigated. Experiments were performed with fixed total polymer concentration of 6 wt%, by varying the PLLA/PLA weight ratio. Blend weight compositions examined were 100/0, 80/20, 50/50, 20/80 and 0/100, at fixed dioxane/water weight ratio (87/13). Cloud point measurements reported that the demixing temperatures of blends are close to PLLA in the same mixed solvent, in line with the calculated spinodals. As regards to foam preparation, above the PLA cloud point, morphology is similar to pure PLLA foams; conversely, below PLA cloud point, the morphology resulted highly inhomogeneous. This behavior could be related to a change in equilibrium conditions occurring close to PLA cloud point. The equilibrium measurements performed gave out results in line with this hypothesis.