Toughness enhancement in polymer blends due to the in-situ formation by chaotic mixing of fine-scale extended structures

Abstract

Experimental results are presented to demonstrate that significant improvements to the impact properties of a polystyrene (PS) matrix can be achieved by the addition of only 9% by volume of low density polyethylene (LDPE). Polymer blends of LDPE and PS were combined in the molten state within a cylindrical cavity where a quiescent, three-dimensional chaotic mixing process was performed. Whereas a minor phase normally adopts the form of highly distributed droplets in conventional processing techniques, minor phase bodies were stretched and folded recursively to yield fine-scale extended and interconnected structures. The structures were largely preserved upon solidification. Impact tests were carried out on specimens which were machined from the solidified blend. Fracture surfaces of the impact test specimens were examined by scanning electron microscopy. Blends achieved a maximum impact toughness 69% higher than that of PS. Results demonstrate potential improvements in properties that may be obtained if favorable and unique microstructures are formed directly in the melt during processing.