Mixing immiscible blends in an intermeshing counter‐rotating twin screw extruder

Abstract

AbstractDomain size of 10% dispersed polystyrene in polyethylene was followed in a 34‐mm intermeshing counter‐rotating twin screw extruder. Variables studied included the effects of barrel temperature, screw speed, viscosity ratio of dispersed‐to‐continuous phase, and parallel melt versus preblended solids feeds. After steady state was achieved, die samples were quenched for later photomicrographing. The extruder was then stopped and quenched, with subsequent pulling of the screws. From 7 to 12 additional samples were taken along the 18/1 L/D extruder for determination of the mechanism of dispersion and dispersed phase domain size by optical microscopy. At low temperatures, the polystyrene tended to fracture with sharp edges. The fine particles formed in the initial breakup underwent no further size reduction. At higher temperatures, fractured segments had rounder edges, but the size of the small domains remained constant throughout the axial length. There was some evidence of flocculation and coalescence prior to exit through the die. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 81–89, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20065