Melt viscosity of polyethylenes

Abstract

The melt viscosity of fractionated and unfractionated polyethylenes at low shear rates have been measured in the temperature range 140–280°C. The melt index is not an adequate measure of melt viscosity determined at low shear rate. From melt viscosity and intrinsic viscosity determinations on fractions an estimate of the degree of long-chain branching can be made. From viscosity measurements at several temperatures between 140 and 280°C. values of the apparent activation energy for fractionated and unfractionated polyethylenes were obtained. The activation energy increases from 8 to 13 kcal. as the weight-average molecular weight increases about 20,000 to about 200,000.