Melt viscosity of polyethylenes. Shear dependence of viscosity

Abstract

Abstract The melt index apparatus has been adapted for use as a simple rheometer. Changes in orifice diameter from 0.0425 to 0.2000 in. and in weight applied to the piston from 250 to 3250 g. permit an effective range of shear stress from 10 4 to 10 6 dynes/cm. 2 With this apparatus, the fluidity of polyethylene as a function of shear stress was shown to be a linear function of the shear stress in the range studied. Consistent data using different orifices were obtained by correcting for the friction between piston and barrel. It was found that two parameters, the fluidity at zero shear rate and the shear‐stress dependence of fluidity, are sufficient for the characterization of the flow behavior of polyethylenes. In order to account for the effect of temperature on the shear dependence of viscous flow, as determined from measurements at several temperatures, two activation energies are needed, one corresponding to each of the two parameters mentioned.