THE EFFECT OF MIXING TIME ON THE MORPHOLOGY OF IMMISCIBLE POLYMER BLENDS

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for t wo immiscible binary polyblend systems, polyamide/polyethersulfone (PA /PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by select ive dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases , shown by the results of PA/PES blends with a viscosity ratio of 0.03 . The lower viscous phase (PA) forms particles, fibrils, and layers su ccessively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase ( PES) appears mainly in the form of particles and directly becomes a co ntinuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is deter mined mainly by the volume fraction of each phase. Particles are the f inal morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixi ng time the same, and any one of these two components is in the form o f particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The co mposition range of cophase continuity is decided not only by the visco sity ratio but also by the mixing time. With increasing mixing time, t his range becomes narrower and finally occurs at volume fraction of 50 /50, no longer affected by the viscosity ratio. (C) 1996 John Wiley & Sons, Inc.