Morphology and rheology of PP/POE blends in high shear stress field

Abstract

Polypropylene (PP)/polyolefin elastomer (POE; ethylene–octene copolymer) blends with varying weight percentages of POE were prepared in a twin-screw extruder and molded through high shear rate injection-molding process. The morphologies and rheology of the PP/POE blends were systematically investigated based on rheological data and experimental analysis. The results indicate that the polymer blends of plastic and rubber in a high shear stress field result in a multilayered microstructure, which can be divided into skin, transitional, shear, and core layers according to the morphology of the dispersed phase. The morphology formation of the dispersed phase depends on the shear field and temperature field in the processing. Morphological evolution of the dispersed POE phases in PP matrix was described and quantified. A dragging ellipsoid model and capillary number were employed to describe the morphological evolution of the dispersed phase, and the morphological parameters were obtained. The results show that the dragging ellipsoid model is well suited to explain the morphological evolution of the dispersed phase in polymer blends molded under high shear rate.

Effect of Mold Temperature on the Impact Behavior and Morphology of Injection Molded Foams Based on Polypropylene Polyethylene–Octene Copolymer Blends

“…Figure 3 shows representative SEM micrographs of both the solid and foamed samples produced with different mold temperature in the Machine direction (MD) plane. This direction was selected because in previous papers [28,29,30] the hierarchical structure of the materials was better observed in this plane.…”

“…In solids, this hierarchy structure, composed by layers, has been well studied [28,29,30]. It is well known that morphology of polymer blends is determined by the flow history and the properties of the components [42].…”

“…The viscosity ratio is crucial. If value p is high, the matrix viscosity is too low to change the shape of a dispersed phase with high viscosity [28,42]. When Ca is above a critical value (dependent on the value of p), the droplet attains a steady shape and orientation, whereas above the critical capillary number the droplet eventually breaks up, by the apparition of a capilarity-wave instability.…”

“…Injection molding is the most extended process in the plastic industry, due to its high versatility (a wide range of part geometries are possible), short cycle time and good surface quality. PP/POE blends have been studied by several authors, such as Li, Liu and Ying [28,29,30], describing the elastomer phase morphology along the profile of the injecting molded solid material. These previous results for solids will be used in the discussion section of this paper.…”

Effect of the elastomer viscosity on the morphology and impact behavior of injection molded foams based on blends of polypropylene and polyolefin elastomers

“…An important aspect to consider is that in this process, the velocity of the polymer filling the mold is not constant. Thus, a shear rate gradient is present, producing a hierarchy morphology 21–23 . Apart from the shear rate, temperature also has a gradient along the mold profile.…”