Ji-Zhao Liang

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.

Elastic behavior of LDPE/HEPE blend melts in capillary extrusion

The studies of the elastic behavior in the capillary flow of LDPE/HDPE blend melts were carried out at a test temperature range from 180 to 200°C and at an apparent shear rate of about 25-120 s -1 . The end-pressure drop (ΔP end ) increased nonlinearly with increasing wall shear stress (τ w ) and achieved a minimum value at a weight fraction (o HD ) of HDPE of 50%. The die-swell ratio (B) increased basically linearly with increasing τ w or ΔP end and achieved a maximum value at o HD of 50%. With the addition of the die length-diameter ratio, the values of B were decreased linearly. At a low shear rate, the temperature sensitivity of the melt die-swell was more significant than at a high shear rate. With increasing o HD , B increased when o HD < 50%, then decreased. B reached a maximum value at o HD of 50% and a fixed apparent shear rate. This phenomenon may be explained by using the theory of viscoelastic competition between components of polymer blend melts. Furthermore, the first normal stress difference (N 1 ) of the sample melts was estimated by using an equation published in a previous work. The results showed that B increased linearly with increasing N 1 .