Prediction of rheological behavior of branched polyethylene from molecular structure

Abstract The general description of steady shear melt viscosity as a function of shear rate for polyethylene, containing any level of long chain branching, in terms of molecular structure is reported. A model, developed previously by B. H. Bersted for the prediction of rheological properties from the molecular structure of linear materials, and which has been subsequently modified by Ram and Pedersen for application to highly branched low‐density polyethylene, is extended to describe the flow behavior of branched high‐density polyethylene. The description of the branched high‐density polyethylenes, which characteristically show dramatic viscosity enhancement relative to linear polyethylene, is effected by considering these materials to be blends of branched and linear species. A logarithmic rule of mixtures was found adequate at all shear rates for the description of blends of branched and linear materials.