Control of extrudate swell and instabilities using a rotating roller die

Abstract

Thermoplastics extruded from dies will always swell and above a critical flow rate display instabilities (sharkskin, stick-spurt or gross melt fracture). Prior research has shown that the best way to suppress these instabilities is to reduce the entry converging angle using a smooth convergence and induce permanent wall slip. In this research we go a step further by allowing the walls to move using a rotating roller die. Thus both extrudate swell and flow instabilities become controllable. This paper presents data to support this claim. The practical benefits are important as stable operation at higher flow rates become permissible. Also, by providing extra control variables, this device becomes a useful tool to help unravel the causes of the various instabilities that arise in polymer melt die extrusion. A first from this research, using this roller die geometry we were able to tease out surface roughness instability with polystyrene hitherto not reported.