Effect of the mixing procedure on the morphology and properties of compatibilized polypropylene/polyamide blends

Blends containing equal amounts of polypropylene (PP) and polycaprolactam (PA6) were prepared by extrusion mixing, using 5% by weight of polystyrene-block-poly(ethylene-stat-butylene)-block-polystyrene, modified by grafting with maleic anhydride (SEBS-MA), as the compatibilizer precursor. The blends were obtained using three mixing procedures, representing different ways of introducing the compatibilizer. The blends were prepared by (A) one-step mixing of the three components, (B) mixing a preblend of SEBS-MA and PP with PA6, and (C) mixing a preblend of SEBS-MA and about one-third of the total amount of PA6 with PP and the rest of the PA6. All of the blends contained dispersed PA6 domains, surrounded by a separate interphase of the self-assembling compatibilizing polymer. The morphology of blends A and B were similar and markedly different from that of blend C, which contained dispersed phase domains of two clearly distinguishable populations. Impact strength and elongation at break were lowest for C. The poor performance of blend C is due to the fact that a considerable fraction of the compatibilizer ended up in small, well dispersed phase domains with a high weight ratio of compatibilizer to PA6. (C) 1998 Elsevier Science Ltd. All rights reserved.