Effect of Die Geometry on Drawdown Force of Polypropylene at Capillary Extrusion

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ABSTRACT Drawdown force, defined as the force needed to stretch a polymer melt uniaxially at capillary extrusion, is investigated using isotactic polypropylene. In this study, we focus on the effect of die geometry on the drawdown force. As similar to the swell ratio, which decreases with increasing die length, the drawdown force is found to increase with the die length. A prolonged residence time in a long die leads to the marked orientation. Consequently, crystallization occurs rapidly after passing through a long die, which is confirmed by wide‐angle X‐ray measurements. Moreover, the rapid crystallization by the addition of a nucleating agent also enhances the drawdown force.

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