Linear low‐density polyethylene/high‐density polyethylene blends: Effect of high‐density polyethylene content on die swell and flow instability

This work aimed to evaluate the effect of high‐density polyethylene (HDPE) content and of shear rate on the die swell and flow instability of linear low‐density polyethylene (LLDPE)/HDPE blends. The results showed that the die swell of the LLDPE/HDPE blends increased with the increase in the shear rate. At high shear rates, the increase in the HDPE content led to an increase in the die swell of LLDPE/HDPE blends. The surface morphology analysis of the extrudates by optical and scanning electron microscopy revealed the presence of sharkskin and stick–slip flow instabilities in LLDPE and LLDPE/HDPE blends at the shear rates investigated. These instabilities were attenuated with the addition of HDPE and almost disappeared in the LLDPE/HDPE blend containing 50 wt% of HDPE.