Rheology, phase morphology, mechanical, impact and thermal properties of polypropylene/metallocene catalysed ethylene 1-octene copolymer blends

Abstract

Blends of a polypropylene (PP) and a metallocene catalysed ethylene–octene copolymer (EOC) were prepared using a single screw extruder fitted with a barrier screw design. The EOC used had 25wt% 1-octene content and the weight fraction of EOC in the blends covered the range 1–30 wt.% Viscosity values for the blends determined experimentally from dual capillary rheological studies were similar to those calculated theoretically using the log additivity principle described by Ferry. This result together with scanning electron microscopy (SEM) observations and evidence from tan δ curves from dynamic mechanical thermal analysis showed PP and EOC to be partially miscible for blends having 10wt% EOC or less. The tensile modulus, break strength and flexural modulus of the blends decreased with respect to virgin PP as the weight fraction of EOC was increased to 30 wt.% The diminution in mechanical properties was concomitant with an initial increase in elongation at break from 40% for neat PP to 140% for the blend with 15wt% EOC before decreasing to 65% when 30wt% EOC was blended. The optimum impact modification of the PP used in this study, in the temperature range −40 to 23°C, was achieved by blending with between 20 and 30wt% EOC.