Phase interactions and structure evolution of heterophasic ethylene–propylene copolymers as a function of system composition

Abstract

Heterophasic copolymers comprised of polypropylene (PP) matrix and ethylene-propylene copolymer (EPC) dispersed phase were investigated with respect to the dispersed phase composition, i.e., ethylene/propylene ratio. The rheological properties, morphology, as well as thermal and mechanical relaxation behavior were studied to describe the structure evolution and phase interactions between the components of the PP copolymers. Decrease of the ethylene content of the EPC leads to a higher matrix-dispersed phase compatibility, as evaluated by the shift of the glass transition temperatures of EPC and PP towards each other. At ethylene content of EPC of 17 wt %, the glass transition temperatures of the both phases merged into a joint relaxation. The effect of the EPC composition on the internal structure of the dispersed domains and on the morphology development of the heterophasic copolymers was demonstrated. Decreasing ethylene content was found to induce a refinement of the dispersed phase with several orders of magnitude down to 0.18 m for propylene-rich EPC. Optical microscopy observations showed that the dispersed propylene-rich phase is preferably rejected at the interlamellar regions of the spherulites and/or at the interspherulitic regions, while the ethylene-rich domains are engulfed within the PP spherulites. Both of these processes impose an additional energetic barrier and influence the spherulite growth rate of the heterophasic materials.

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.…”

“…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.…”

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

“…A look at the corresponding DSC results in Table 3 however shows the absence of crystalline PE even at higher C2(XCS), quite in contrast to results normally found for ZNC-based EP-HECOs. Doshev et al [3] reports clear melting points for the PE phase of ZNC-grades from 70 wt% C2(XS) upwards, i.e. very close to the composition of PP/EP68.…”

“…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.…”