Stability of the co-continuous morphology during melt mixing for poly(epsilon-caprolactone)/polystyrene blends

Over the last 10 years, research into co-continuous polymer blends has been intense. Despite these efforts, there are very few detailed studies on the stability of this complex morphology. In this work, blends of poly(e-caprolactone) and polystyrene were melt-mixed in an internal mixer for time intervals of 0.5-120 min at set temperatures of 140 and 170 degrees C, and the effect of the mixing time on the co-continuous morphology was studied. This blend system was chosen because each component could be selectively dissolved and this allowed for a complete study of the co-continuous region. The phase continuity was measured with a solvent-extraction gravimetric technique, and the concentration range for co-continuity was determined. The phase size and phase size distribution were obtained with the mercury intrusion porosimetry technique. The results indicate that the co-continuous morphology forms very early in the mixing process and achieves a stable morphology within the first 5 min of mixing for virtually all the co-continuous compositions. For all cases studied, the co-continuous morphology remains unchanged over mixing times as long as 1-2 h. These results support the notion of a stable steady-state formation of co-continuous morphologies during melt mixing similar to that observed for matrix/dispersed phase type blends. (c) 2007 Wiley Periodicals, Inc.