Impact of Mixing Method on Rheological Instability for Binary Mixture of Linear Low‐Density Polyethylene.

Abstract: The impact of different mixing methods on flow instability in capillary extrusion was examined using binary mixtures of linear low‐density polyethylene with different molecular weights. The polymers were blended using a single‐screw extruder, a twin‐screw extruder, and a twin‐screw mixer. The onset of flow instability changed depending on the mixing method used, even though their linear viscoelastic properties were almost identical. The mixtures that were subjected to mixing methods with weak mixing capability exhibit sharkskin failure even at low shear stress and low values of the maximum draw ratio without rupture in the molten state. The results suggested that mechanically weak points were present, which led to cohesive failure at the strand surface following abrupt stretching at the die exit (i.e., sharkskin failure). In contrast, the mixture that was subjected to thorough mixing exhibited smooth surface at high shear stress and a large maximum draw ratio. [ABSTRACT FROM AUTHOR]