Flow visualization and extrudate swell of natural rubber in a capillary rheometer: Effect of die/barrel system

An investigation was carried out to examine the effect of die/barrel system on the flow patterns and extrudate swell of natural rubber in the barrel o f a capillary rheometer, using a colored tracer as the visualization techni que. The capillary rheometer used in this work had two dies located along t he barrel, which is novel in rheometer design. The flow of the rubber in th e upper barrel was dependent on the piston/barrel action and changed with p iston displacement, whereas the complexity of the flow in the lower barrel was dependent not only on the piston displacement, but also on the geometry of the upper die design. The flow patterns that developed in the whole bar rel were independent of the die located at the bottom of the barrel. In add ition, the change in extrudate swell was associated with the flow occurring in the barrel, residence time, elastic characteristic, and the temperature rise during the flow. It was concluded that the general style of the flow patterns of natural rubber was greatly dependent on the die geometry that t he material had previously moved past. (C) 2001 John Wiley & Sons, Inc.