MECHANICAL-PROPERTIES AND MORPHOLOGY OF PP SEBS PC BLENDS

Rubber toughening of thermoplastic polymers always decreases the tensi le and flexural properties. In this article, an attempt is made to imp rove the tensile and flexural properties of a rubber-toughened polymer system viz., polypropylene (PP)/styrene-ethylene-butylene-styrene tri -block copolymer (SEBS) binary blend by blending a rigid polymer viz., polycarbonate (PC) with this binary system. The PP/SEBS blend with a blending ratio fixed at three levels, namely 95/5, 90/10, and 80/20, w as melt mixed with 0-30 wt% PC to generate the various blend compositi ons studied. This choice of compositions enabled us to show how the me chanical properties varied as a function of (1) PP/SEBS ratio at a con stant PC content and (2) PC content at a constant PP/SEBS ratio of the blend. Data on the corresponding binary blends, namely PP/SEBS and PP /PC, are also presented and discussed as reference systems. The data a re discussed in detail for the effect of each component of the blend. As regards the morphology, some distinct changes were seen in the midd le of composition ranges of the additives, i.e., around 10 to 20% PC l evel, and 95/5 and 90/10 PP/SEBS ratios. Variation of mechanical prope rties in the respective composition ranges are found consistent with t he variations of blend morphology. Hence, a correlation of morphology and the properties is discussed. Furthermore, the results suggest stro nger interfacial interaction between SEBS and PP than that between PC and PP. Scanning electron microscopic studies of appropriately etched impact fractured samples reveal the existence of composite droplets of SEBS and PC embedded in PP matrix, with SEBS forming the outer envelo pe around PC. (C) 1994 John Wiley & Sons, Inc.