Impact of controlled extensional flow during extrusion of PP, PVDF and LDPE

Abstract

The structure and properties of semi-crystalline polymers can be drastically tailored by extensional flows. In this work, polypropylene (PP), Polyvinylidene fluoride (PVDF) and Low Density Polyethylene (LDPE) were melt extruded through a sequence of rings designed to apply controlled extensional flows in the polymer melts. The effects of extensional flow on the structure and properties of the extruded filaments were then evaluated by mechanical tensile tests, dynamic-mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC). The DMA and tensile tests revealed a significant increase in terms of static and dynamic moduli for the polymers extruded through the extensional flow device. PP, PVDF and LDPE had their dynamic moduli enhanced 19%, 40% and 77%, respectively. These results were ascribed to the enhancement in crystallinity and orientation degree of the polymer chains induced by the extensional flow. The crystallinity was increased around 9% for PP, PVDF and LDPE extruded under extensional conditions.

Keywords:
extensional flow; extrusion; semi-crystalline polymers; crystallinity increase