Prediction of the onset of extrudate distortion in polyethylenes from rheological data

Abstract

Abstract An extensive set of rheological data, including steady shear, normal stress, and oscillatory response functions, have been obtained for several polyethylene melts, and a modified form of the Spriggs nonlinear co‐rotational model has been used to represent the data. The resulting model was used to predict the transient stress response of the melts in a simplified model of the extrusion process, with a resulting criterion for the onset of melt distortion in terms of readily evaluated rheological parameters. The predicted occurrence of melt distortion based on this criterion agreed well with observations for the polymers in this study as well as for a variety of other polymers reported in the literature.