The influence of titanium dioxide on the rheological and extrusion properties of polymer melts

Abstract

An experimental study of the influence of titanium dioxide (TiO2) on the rheological and extrusion properties of five polymer melts (two low-density polyethylenes, two high-density polyethylenes, and a polystyrene) has been carried out. Increasing TiO2 loading increases the shear viscosity η, with the extent of increase being greater at lower shear rates. At moderate and high TiO2 loadings, the filled melts may possess yield values. Empirical equations relating viscosity to filler loading have been developed. The first normal stress difference was measured for the melts and found to increase with increasing TiO2 loading. However, the extent of increase was less than found for the viscosity function and interpretation in terms of the theory of viscoelasticity suggests that the characteristic relaxation time of the melts decreases with increasing TiO2 level. Empirical equations relating the first normal stress difference coefficient to volume fraction of the filler have been developed. Addition of TiO2 is found to decrease extrudate swell and retard the occurrence of extrudate distortion.