Analysis of the free surface instabilities in extrusion and coextrusion flows for metallocene based polyolefins

Abstract

The effect of die design and wall slip on the die drool phenomenon was investigated for metallocene based LLDPE. It has been found that die exit opening and wall slip can significantly reduce the die drool phenomenon. Moreover, theoretical research has revealed that die drool onset can be explained by the negative/non-monotonic pressure profile generated inside the die and/or at the die exit region due to melt elasticity. In the second part of the paper, recently proposed new slip model based on 'effective continuum methods' was developed and used for investigation of process aids interactions with polymer melts in single as well as multi-layer flows. Specific attention has been paid to understanding the role of process aids on stabilization of the zig-zag type of interfacial instabilities in film blowing coextrusion.