Capillary Extrusion Studies of LLDPE/LDPE Blends: Effects of Manufacturing Technology of LLDPE and Long Chain Branching

The processing behavior of a number of LLDPE/LDPE blends with emphasis on the effects of manufacturing technology of LLDPE and long chain branching is presented. A single low-density polyethylene was blended with two Ziegler-Natta linear-low-density polyethylenes LLDPE's and two metallocene-LLDPE's having distinctly different molecular structures. The weight fractions of the LDPEs used in the blends were 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 50 wt.% and 75 wt.%. Capillary extrusion reveals that the onset of sharkskin and gross melt fracture are slightly influenced with the addition of LDPE into LLDPE. However, the amplitude of the oscillations in the stick-slip flow regime was found to scale well with the weight fraction of LDPE even at amounts as low as 1 wt.%. Furthermore, it was observed that the onset of this flow regime was shifted to higher shear rates with increase of LDPE content. Shear rheology was found to be insensitive to detect small levels of LDPE. On the other hand, extensional rheology was found to be capable of detecting levels of LDPE as low as 1 wt.% at high Hencky strain rates (typically greater than 5 s−1) although only for certain blends.