Prediction of Polyethylene Molecular Weight and Molecular Weight Distribution Using Capillary Rheometer

Polyethylene is characterized by molecular weight (MW), molecular weight distribution (MWD), and density. Melt index (MI ₂ ) is measured in the quality control (QC) lab and is used as an indication of resin MW. Melt flow ratio (MFR or MI ₂₀ /MI ₂ ) is a calculated QC lab number, which is used as an indication of MWD. Density is a measure of crystallinity. This article shows that a capillary rheometer can provide a fast and reliable method on a production line to control MW and MWD by predicting MI ₂ and MI ₂₀ for a resin within specific ranges of density, melt index and equipment/catalysts.