Die swell–molecular structure model for linear polyethylene

Abstract

AbstractAn empirical relation between capillary die swell and molecular structure, defined by total weight average molecular weight (MwT), molecular weight distribution (MWD), and fraction high molecular weight content (FRB with MwB ≥ 164.000) is established. Via a Box–Behnken experimental design setup blends of Ziegler–Natta catalyzed linear polyethylenes are prepared to allow a statistical analysis of the die swell–molecular structure relation. The contradicting results of Rogers and Mendelson et al. for the die swell–molecular structure relation are shown to be compatible and are to be considered as special cases of the general model presented here. The existence of a die swell maximum is shown. The relative amount (FRB) and size (MwB) of the high molecular weight molecules define this elastic property of linear polyethylene melts.