Phase structure in polypropylene/PA6/SEBS blends

A range of blends based on 70% by weight of polypropylene (PP) with 30% by weight dispersed phase were produced via melt blending in a co-rotating twi n screw extruder. The dispersed phase composition was varied from pure Poly amide 6 (PA6) over a range of PA6:SEBS (poly[styrene-b-(ethylene-co-butylen e)-b-styrene]) ratios, using both reactive (maleic anhydride grafted) and n on-reactive SEES elastomers. The two-component PP/30%PA6 blend was unstable towards coalescence during melt processing and consequently exhibited a ve ry coarse morphology and poor mechanical properties. Whereas a three-compon ent PP/15%PA6/15%SEBS blend containing non-reactive SEES exhibited two disp ersed phases; a PA6 phase with a size-scale of 1-5 mu m and an SEES phase w ith a size-scale of less than or equal to 0.5 mu m. As a result both tensil e and impact properties were much improved compared to the 70/30 blend. The use of reactive SEBS-g-MA resulted in the formation of dispersed phases co nsisting of PA6 particles encapsulated with SEES. Varying the fraction of S EBS-g-MA in the dispersed phase allowed a manipulation of the dispersed pha se structure, to form either core-shell PA6/SEBS particles or larger, more complex agglomerated PA6/SEBS structures. The core-shell particles resulted in an increase in charpy impact strength of greater than an order of magni tude, compared to the PP matrix, and almost equivalent tensile properties. The larger agglomerated structures also generated very large increases in i mpact strength, of up to thirty-fold, but only at the expense of significan t reductions in tensile modulus and yield stress. (C) 1999 Elsevier Science Ltd. All rights reserved.