Polypropylene/polyethylene blends as models for high‐impact propylene–ethylene copolymers, part 1: Interaction between rheology and morphology

Abstract

In this work, composition effects on interfacial tension and morphology of binary polyolefin blends were studied using rheology and electron microscopy. The amount of dispersed phase (5-30 wt %) and its type [ethylene-octene copolymer, linear lowdensity polyethylene (LLDPE), and high-density polyethylene] was varied, and the influence of different matrix materials was also studied by using a polypropylene homopolymer and a ethylene-propylene (EP) random copolymer. The particle size distribution of the blends was determined using micrographs from transmission electron microscopy (TEM). A clear matrix effect on the flow behavior could be found from the viscosity curves of the blends. Analyzing the viscosity of the blends applying the logarithmic mixing rule indicated a partial miscibility of the EP random copolymer with low amounts of the LLDPE in the melt. Micrographs from TEM also showed a clear difference in morphology if the base polymer is changed, with PE lamellae growing out of the inclusions or being present directly embedded in the matrix. To verify these findings, the interfacial tension was determined. The applicability of Palierne's emulsion model was found to be limited for such complex systems, whereas Gramespacher-Meissner analysis led to interfacial tensions comparable with those already reported in the literature. The improved compatibility when changing the matrix polymer from the homopolymer to the random copolymer allows the development of multiphase materials with finer phase structure, which will also result in improved mechanical and optical performance.

Polypropylene/ethylene-propylene rubber (PP/EPR) blends for the automotive industry: Basic correlations between EPR-design and shrinkage

“…Scanning Electron Microscopy (SEM) investigations of the polymers showed that the melt viscosity of the dispersed EPR phase, represented by the intrinsic viscosity of XCS fraction, significantly affects the size and distribution of EPR particles. This is in line with theory and was reported by a number of research groups (compare [17][18][19][20][21][22] and [25][26][27][28]). Unlike in previous studies, the particles' cross sections were not considered to be circular but taken to be elliptically shaped as a result of the orientation in the processing step.…”

“…Furthermore, the particles are smaller in the high shear skin region than in the core of the specimens. Although this is in line with literature (compare [17][18][19][20][21][22] and [25][26][27][28]), the determined diameters are not reflecting the actual shape of EPR the particles. The particles are oriented and elongated during the filling of the mold.…”

“…nylon and polyester as the matrix and EPR as the dispersed phase. More relevant for the present study, in which matrix and disperse phase are very similar, are papers like the ones by Mighri et al [25] and Kock et al [26]. None of these studies investigated reactorbased heterophasic systems like the ones in this study.…”

Structure-property relations of heterophasic ethylene-propylene copolymers based on a single-site catalyst

“…In general it should be noted that while numerous reports deal with the effect of viscosity ratio of PP/EPR blend systems as well as their ternary counterparts, PP/EPR/PE blends, on morphology [4,15,16,[25][26][27], the effect of EPR composition on the same has been studied significantly less [2,3,5,[28][29][30]. In both cases a decisive parameter of polymer blend theory is modified, and both for the viscosity ratio as for the compatibility the change can be effected for the matrix component as well as for the disperse one.…”

Simultaneously enhancing strength and toughness for impact polypropylene copolymers by regulating the dispersed phase with high density polyethylene

“…[32][33][34] Since HPP and HDPE are completely incompatible, one can add compatibilizer (such as block polymers by copolymerization) into them to reduce interfacial tension. Generally, interfacial tension of the components is presumed to be the main driving force of morphology evolution for a multi-component system.…”