Measurement of the rheological properties of polymer melts with slit rheometer. I. Homopolymer systems

Abstract

synopsisTwo slit dies have been designed, having aspect ratios of 10 and 20. Three melt pressure transducers were flush-mounted on the long side of the rectangular slot, along the longitudinal centerline of each die. The dies were then used to measure wall normal stresses along the longitudinal direction of polymer melts flowing through the thin slit. The polymeric materials investigated were high-density polyethylene, lowdensity polyethylene, polypropylene, and polystyrene. The measurement of wall normal stresses were used to determine the rheological properties of melts, namely, the melt viscosity from the slope of axial pressure profiles and the melt elasticity from exit pressures. The present study shows that the rheological properties determined from the slit rheometer are in good agreement with those from the capillary rheometer reported in the author's earlier papers. Therefore it may be concluded that a slit die also may be used as a means of characterizing polymeric materials by their viscous and elastic properties in the molten state.

Wall normal stresses and die swell behavior of viscoelastic polymeric melts in flow through converging ducts

“…In view of the previous studies which were concerned with the wall normal stress measurements in straight circular tubes (Han et al, 1969; Han et al, 1971) and in straight rectangular ducts (Han, 1971a;1971b), the results obtained in this study were quite unusual in both the distributions of wall normal stress and extrudate swell behavior. In this paper some of the results will be presented that seem worth reporting.…”

“…It is a wellestablished fact that the wall normal stress decreases as a melt flows through a duct of uniform cross section (Han et al, 1969;1971;Han, 1971a;1971b). Therefore, although the cross section of the converging channel changes from the die entrance, there would be a region in the die which is still influenced by the upstream flow regime which gives rise to a gradual drop in pressure.…”

“…From there, melt flows into the die section. The arrangement of these pieces of equipment is essentially the same as that described in a recent paper by Han (1971a).…”

Flow of viscoelastic polymeric melts through converging ducts

“…This is because, for fully-developed flow in a circular tube with uniform cross is related to the isotropic pressure p(r,z) by S,r(r,z) = -p(r,z) + ~,,(r) [3] in which %. This is because, for fully-developed flow in a circular tube with uniform cross is related to the isotropic pressure p(r,z) by S,r(r,z) = -p(r,z) + ~,,(r) [3] in which %.…”

“…In recent years, an.intensive study, notably by Han and bis coworkers (1)(2)(3)(4)(5) has been made of the rheological significance of wall normal stress measurernents in viseometric flow fields. These authors measured wall normal stresses in the fully developed region of a circular tube and of a thin slit die.…”