Phase Segregation in Polystyrene−Polylactide Blends

Spun-cast films of polystyrene (PS) blended with polylactide (PLA) were visualized and characterized using atomic force microscopy (AFM) and synchrotron-based X-ray photoemission electron microscopy (X-PEEM). The composition of the two polymers in these systems was determined by quantitative chemical analysis of near-edge X-ray absorption signals recorded with X-PEEM. The surface morphology depends on the ratio of the two components, the total polymer concentration, and the temperature of vacuum annealing. For most of the blends examined, PS is the continuous phase with PLA existing in discrete domains or segregated to the air−polymer interface. Phase segregation was improved with further annealing. A phase inversion occurred when films of a 40:60 PS:PLA blend (0.7 wt % loading) were annealed above the glass transition temperature (T g) of PLA.