Correlation between steady state flow curve and molecular weight distribution for polyethylene melts

This article uses Graessley's theory of viscosity to predict the flow curve for several high‐density and low‐density polyethylene melts using the molecular weight distribution data obtained from the gel permeation chromatograph. The agreement with the experimental flow curve obtained from the Weissenberg rheogoniometer and the Instron rheometer was not quantitative for many high‐density polyethylenes studied here. For the low‐density polyethylenes, it was shown that the agreement between the theory and the experiment was good even though the molecular weight distribution data were not corrected for long‐chain branching. For these samples, the experimental relaxation time τ0 obtained by superposition of the data with the theoretical master curve was of the order of the Rouse relaxation time τR. The systematic increase in the ratio τR/τ0 was ascribed to the increase in the molecular weight or to the increased number of long‐chain branches.