Structural development and mechanical properties on immiscible and miscible blends from isotactic polypropylene and ethylene-1-hexene copolymers under uniaxial drawing

Isotactic polypropylene and ethylene-1-hexene copolymers containing 32 and 57 mol% of 1-hexene copolymers blends (i-PP/EH32 and i-PP/EH57) were prepared by solution blending, precipitating followed by drying and hot pressing. The two blends were subject to investigation on structure and mechanical properties of these blends under uniaxial drawing. The i-PP/EH32 and i-PP/EH57 represented the immiscible and miscible blends, respectively. The tensile stresses and strains at breaking point of i-PP/EH57 were remarkably higher than those of i-PP/EH32 at room temperature. From wide-angle X-ray diffraction (WAXD) measurement, it was observed that the orientation of crystallites occurred early and then propagated gradually up to about drawing ratio 8 because chains of EH57 copolymer were incorporated into the amorphous regions between lamellae of i-PP. In the WAXD patterns of i-PP/EH57, the oriented spot reflections coexsisted with unoriented ring reflections up to draw ratio higher than in pure i-PP. On the other hand, the two-phase structure was observed from TEM and AFM in i-PP/EH32, and on the drawing, separation at the interface between two-phase was observed in i-PP/EH32 even at the low strain. (C) 2001 Elsevier Science Ltd. All rights reserved.