Quantitative characterization of dispersed particle size, size distribution, and matrix ligament thickness in polypropylene blended with metallocene ethylene–octene copolymers

Abstract

The average rubber particle size, size distribution, and matrix ligament thickness between particles in polypropylene blends containing metallocene catalyzed ethylene-octene copolymers have been quantitatively analyzed, as functions of blend composition and phase viscosity ratio. Comparison has been made between experimental data and those predicted from a number of theoretical models. All blends showed two-phase morphology, with interestingly a bimodal distribution of the rubber particle size. The ranges and averages of rubber particle size were mainly determined by blend composition and viscosity ratio between the phases, irrespective of comonomer content along the rubber chains. The logarithmic relationship between the matrix ligament thickness and rubber concentration was observed. The values of ligament thickness obtained from the experiments and theoretical models were not in agreement.

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

“…with increasing melt viscosity ratio between the phases. This is completely in line with previous experience [19,20]. Furthermore, the particles are smaller in the high shear skin region than in the core of the specimens.…”

“…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.…”

“…As both matrix viscosity and the composition of the EPR is similar for all samples the phase viscosity ratio between matrix and rubber can be assumed to be the driving force for this development [17][18][19][20][21][22]. For heterophasic polymer systems like the investigated ethylene-propylene copolymers (also termed rTPOs for 'reactor thermoplastic polyolefins') the viscosity ratio " between dispersed phase and matrix phase is known to control the final morphology.…”

“…Distribution of particle aspect ratio (a) and particle size (b) for the nucleated and non-nucleated version of sample IV2.2 D w and in volume D v were evaluated according to [19] and [20] as Equation (5): Average particle diameters in number D n (5)…”