The early stage of the morphology development of immiscible polymer blendsduring melt blending: Compatibilized vs. uncompatibilized blends

The early stage of the morphology development has been studied for the blen ding of two immiscible polymers. Controlled experiments were carried out in a batch mixer in such a way that the rate of melting was low enough to fol low up the morphology development of dilute and concentrated systems. For a dilute or semidilute polypropylene and polyamide 6 (wPP/PA6) blend with 0. 5, 5, or 10 wt % PA6, particles formed in the very early stage of melt blen ding were very small, of the order of 0.25 to 0.3 mum in radius. They immed iately began to grow in size when no compatibilizer was added, indicative o f coalescence even in the very early stage of melt blending and/or in very dilute systems (0.5 wt % PA6). Further growth of the particles was eliminat ed with the introduction of a graft copolymer compatibilizer providing evid ence of the stabilizing effect of the copolymer from the very beginning of melting blending. However, the behavior of the morphology development of a concentrated PP/PA6 (80/20) system was similar to that reported in the lite rature. The average radius of the particles of the uncompatibilized blend d ecreased with increasing mixing time, whereas that of the compatibilized bl end remained almost constant during mixing. The most favorable conditions t o obtain a fine morphology seems to be the following: rate of melting/plast ification of pellets < rate of dispersion (deformation + breakup) of the po lymer melt to small particles < rate of stabilization (with an adequate cop olymer). (C) 2001 John Wiley & Sons, Inc.