Melt rheology and extrudate swell of sodium chloride-filled low-density polyethylene: Effects of content and size of salt particles

The rheological properties in terms of melt rheology and extrudate swell of low-density polyethylene (LDPE) filled with sodium chloride (NaCl) of varying particle size (i.e., 45, 75, and 125 μm) in the range of 5-25 wt.% were investigated by capillary rheometry. The real shear stress increased monotonously with increasing apparent shear rate, with the rate of change decreasing with increasing apparent shear rate. At an apparent shear rate greater than about 400 s−1, the real shear stress increased with increasing salt content and, at a given apparent shear rate, the real shear stress increased slightly with increasing salt particle size. The shear viscosity decreased monotonously with increasing real shear rate. Regardless of the salt content, the extrudate swell increased with the initial increase in the apparent shear rate to reach a plateau value. After a critical apparent shear rate in the range of 500-1200 s−1, and regardless of the salt particle size, the extrudate swell decreased with increasing salt content. Lastly, the extrudate swell tended to be suppressed when a capillary die with a high L/D ratio was used.