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

Two 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, low-density 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.