A MODEL FOR THE DESCRIPTION OF THE RHEOLO GICAL PROPERTIES OF BLENDS FROM HDPE AND LONG-CHAIN-BRANCHED LLDPE

The rheological properties of blends of high-density polyethylene (HDP E) and linear polyethylene of low density with an amount of long-chain branching (HBPE) synthesized with metallocene catalysts were investig ated regarding the dependence of the shear viscosity from the shear ra te over the whole composition range. While the pure HDPE shows a stron g decrease in viscosity with increasing shear rate, the decrease for H BPE is much less distinctive. For a shear rate of about 300 s(-1) both products show similar viscosities. The viscosities of the blends, in dependence from the shear rate, show a nonlinear change between the ch aracteristics of the pure components HDPE and HBPE. This behaviour cou ld be described with a mathematical model, for which especially ration al functions together with often used rheological model terms gave goo d results. Finally, besides the decrease of the viscosity with increas ing shear rate, the exponent in the Ostwald-de Waele law was discussed as measure for the intrinsic viscosity. The threshold value, i.e. the Merrington effect during extrusion, was calculated as measure for the elastic amounts in the polymer melt, and their dependence from the sh ear rate and from the composition was expressed mathematically and dis cussed. It was observed that the treshold value shows a less significa nt change in dependence from the shear rate than the pure components d o.