Flow‐induced solidification of high‐impact polypropylene copolymer compositions: Morphological and mechanical effects

Abstract

Polypropylene-based impact copolymers are a complex composition of matrix material, a dispersed phase and many optional modifiers. The final heterophasic morphology of such systems is influenced significantly by the processing step, adding an additional level of complexity to understanding the structure-property relation. This topic has hardly been studied so far. The effect of thermal history and shear flow on the solidification process of three different compositions of a polypropylene-based impact copolymer, i.e., one base material and two compounds with either high density polyethylene or ethylene-co-octene added, is investigated. Samples are examined using differential scanning calorimetry, extended dilatometry, transmissions electron microscopy, and finally, tensile testing. With flow, the materials show pronounced flow-enhanced crystallization of the matrix material and deformed filler content. Compared to the base polymer, the stress-strain response of the compounded samples shows a lower yield stress and more pronounced influence of shear, reflected in the increasing strain hardening modulus.

Designing polymer crystallinity: An industrial perspective

“…Examples of research in this area exist for quite some time and with numerous polymer combinations like poly(ethylene glycol) with PLA and iPP with PA‐6, but systematic studies of interfacial effects are rare. Even more interesting and definitely relevant are cases involving phase separation during crystallization or phase structure changes as a result of processing, where completely unexpected phenomena with massive consequence for mechanics and optics may occur.…”

Continuous Cooling Curve Diagrams of Isotactic-Polypropylene/Polyethylene Blends: Mutual Nucleating Effects under Fast Cooling Conditions

“…Despite this, some interesting mutual nucleating effects between the two polymers can arise. In particular, epitaxial growth of PE onto polypropylene (and vice versa) has been extensively documented in oriented systems, establishing the contact planes between the two structures. , Flow fields in typical polymer processing (e.g., injection molding or extrusion) cause chain stretching and orientation, favoring epitaxy of the PE phase on the oriented PP crystals, when crystallized at higher temperatures. − The occurrence of epitaxial crystallization in the flow-oriented specimen significantly improves the interfacial adhesion between the two phases, leading to a remarkable enhancement in both strength and toughness of the material. − …”

Effect of shear rate and pressure on the crystallization of PP nanocomposites and PP/PET polymer blend nanocomposites

“…While the relationship between morphology and blend structure and final properties has been studied extensively, the effect of processing conditions on the final morphology and crystallinity has been treated far less. During processing polymer materials are submitted to high pressures, shear rates and cooling rates that can have a strong influence on the crystalline morphology and, in the case of polymorphic polymers, different crystalline phases are developed depending on the processing conditions [10][11][12][13][14][15][16].…”

“…The effect of shear rate and pressure was also studied in a multiphasic system constituted by an ethylene-propene copolymer, which was modified by adding ethylene-co-octene (EOC) or high-density polyethylene [16]. The final morphology of the samples obtained using different shear rates was investigated by TEM, observing that in some cases, the dispersed phase was oriented in the direction of flow.…”