In this work, the capillary flow of high-density polyethylene (HDPE) melts filled with lamellar particles of talc was investigated both at high and low flow rates. Different talc contents (up to 12.5 vol.% in the melt) were considered. A capillary rheometer, equipped with cylindrical dies and operating at constant-piston-velocity, and a melt flow indexer, for ISO 1133 melt volume-flow rate (MVR) tests, were used to examine high (up to and beyond the onset of “melt fracture” phenomena) and low flow rates, respectively. From capillary rheometer tests, data of steady-state shear viscosity and die entrance pressure drops were measured, with two different die diameters, and related to the results from the MVR experiments. At high flow rates, the presence of lamellar particles of talc in the HDPE melt promotes: i) the suppression of “melt fracture” phenomena; ii) opposite effects on steady-state shear viscosity and die entrance pressure drops, namely a slight decrease and a pronounced increase for the former and the latter flow property, respectively, in the stable-flow region. MVR-data seem to be controlled by the extent of the localized pressure drops in the converging flow at the die entrance. The results are discussed by referring also to electron microscopy analyses on cryo-fractured surfaces obtained from the extrudates formed after the flow through the capillary.
Capillary flow of HDPE melts filled with lamellar rigid micro-particles
F. Baldi
;
2018-01-01
Abstract
In this work, the capillary flow of high-density polyethylene (HDPE) melts filled with lamellar particles of talc was investigated both at high and low flow rates. Different talc contents (up to 12.5 vol.% in the melt) were considered. A capillary rheometer, equipped with cylindrical dies and operating at constant-piston-velocity, and a melt flow indexer, for ISO 1133 melt volume-flow rate (MVR) tests, were used to examine high (up to and beyond the onset of “melt fracture” phenomena) and low flow rates, respectively. From capillary rheometer tests, data of steady-state shear viscosity and die entrance pressure drops were measured, with two different die diameters, and related to the results from the MVR experiments. At high flow rates, the presence of lamellar particles of talc in the HDPE melt promotes: i) the suppression of “melt fracture” phenomena; ii) opposite effects on steady-state shear viscosity and die entrance pressure drops, namely a slight decrease and a pronounced increase for the former and the latter flow property, respectively, in the stable-flow region. MVR-data seem to be controlled by the extent of the localized pressure drops in the converging flow at the die entrance. The results are discussed by referring also to electron microscopy analyses on cryo-fractured surfaces obtained from the extrudates formed after the flow through the capillary.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
