Die swell of filled polymer melts

Abstract

The Barus effect in polypropylene and polystyrene blended with a variety of fillers at various concentrations was investigated using a capillary extrusion rheometer. If the die swellα is defined as the square of the ratio of the extrudate diameterd to the die diameterD, it is found to depend on the apparent shear stressτ′ _W . Below a certain value ofτ′ _w the relationα =B τ′ ^A _B applies. The die swell,α _M , of a filled polymer depends on the type, size and volume fraction of the filler. In particular,A increases as the volume fraction increases and is largest for powders, smaller for flakes and smallest for fibres, whereasB shows the opposite trend but to a lesser extent.