Melt rheology and extrudate swell of low-density polyethylene/ethylene–octene copolymer blends

Abstract

The melt rheological and extrudate swelling behavior of neat low-density polyethylene (LDPE) and blends of LDPE and ethylene–octene copolymer (EOC) was investigated using capillary rheometry at 185.0±0.5 °C. Dies having different length-to-inner diameter ( L/D) ratios were used (i.e., 5/1, 10/11, 10/2, and 30/2 mm/mm, respectively). For a given sample material, the real shear stress was observed to increase with increasing real shear rate, and, for a given real shear rate, the real shear stress was generally observed to increase with the addition and increasing amount of EOC. All of the sample materials exhibited the shear-thinning behavior. Both the tensile stress and the elongational viscosity were found to decrease with increasing elongational rate. Generally, both the tensile stress and the elongational viscosity increased with the addtion and increasing amount of EOC, with an exception for the 85/15 and 80/20 LDPE/EOC blends which exhibited a reversed order. Lastly, the extent of extrudate swelling of the sample materials in the small dies (i.e., inner diameter=1 mm) was greater than that in the larger ones (i.e., inner diameter=2 mm) and the use of a longer die also helped suppress the extent of the extrudate swelling.