Origin of Reduction in Extrudate Swell of Molten Polymer by Adding of Rigid Fillers

Abstract

The effect of rigid fillers having various shapes and sizes on the extrudate swell of molten polymer was investigated. High-density polyethylene (PE) was used as the matrix polymer to quantify the swell behaviors. The shear viscosity of PE was almost unaffected via the addition of any fillers. However, the swell ratio decreased in the presence of fillers. In particular, the swell ratio was decreased by increasing the aspect ratio of fibrous fillers and the suppression of the swell hardly changed with the size of particle fillers. The first normal stress difference that can quantify the extension of polymer chains under shear flow, changed negligibly in spite of the presence of particle and fibrous fillers. On the other hand, the orientation of fibrous fillers along flow direction was clearly demonstrated based on their dispersion state in the extrudate. The swell of molten polymer containing fillers was greatly reduced by increasing the aspect ratio of fibrous fillers, because the constriction of the oriented polymer chains at die exit was suppressed by sticking on the surface of oriented fibrous fillers.