Influence of filters in the die entrance region on gross melt fracture: extrudate and flow visualization

Abstract

The purpose of the present work is to analyze the influence of filters in the die entrance region on gross melt fracture. Various experimental techniques will enable gross melt fracture to be identified and characterized. First, capillary rheometer experiments have been performed with two natural linear and star-branched styrene butadiene rubber copolymers (SBR). The succession and evolution of the different flow defects have been clearly identified. Whatever the microstructure of the polymer melts is, it was found that filtering significantly reduces the severity of the gross melt fracture defect. To explain the possible mechanism for the effect of the filters, rheological measurements using a parallel-plate rheometer have been carried out. Then, we have reported flow visualization experiments on the linear SBR copolymer through a transparent slit die attached to a capillary rheometer. Instabilities are generated in the upstream region for the flow regimes at which melt fracture appears. By stacking filters at the die entrance, the stream lines have been partially stabilized and the extrudate samples less distorted. Consequently, these results emphasize that gross melt fracture is attributed to instabilities developing in the elongational flow field upstream the die entrance.