Die-swell behavior of glass bead-filled low-density polyethylene composite melts at high extrusion rates

The extrudate swell behavior of glass bead-filled low-density polyethylene (LDPE) composite melts was investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 140 to 170 °C. The results show that the die swell ratio (B) of the melts increases nonlinearly with increasing apparent shear rates for the system filled with the surface of glass beads pretreated with a silane coupling agent, while the B for the system filled with uncoated particles remains almost constant when the true wall shear rate is greater than 2000 s^-1 at a constant temperature. The values of B for both the pure LDPE and the filled systems decreases linearly with an increase of the temperature and an increase of the die diameter at fixed shear rates, and the sensitivity of B on the die diameter and temperature for the former is higher than that of the latter. Furthermore, the effect of the filler content on B is insignificant, while the values of B decreases, obviously, with an increasing glass bead diameter (d) when d is smaller than 50 μm; then B varies slightly with d.