Influence of composition distribution and branch content on the miscibility of m-LLDPE and HDPE blends: Rheological investigation

The miscibility of metallocene linear low-density polyethylene (m-LLDPE) and Ziegler-Natta LLDPE (ZN-LLDPE) with linear high-density polyethylene (HDPE) was studied. The influences of composition distribution (CD) and branch content (BC) on the miscibility of m-LLDPE and ZN-LLDPE with HDPE were investigated with rheological methods. The m-LLDPEs (BC = 13.2 CH₃/1000 C) and ZN-LLDPE (BC = 14.5 CH₃/1000 C) of similar molecular weights were paired to study one molecular variable at a time. Melt blending was carried out in a Haake Poly Drive at 190 °C in the presence of 1000 ppm of antioxidants. Dynamic and steady shear measurements were performed in a Rheometrics ARES at 190 °C. The miscibilities of blends were revealed by the dependence of their η_o, η′, N₁ and G′ on blend composition and from predictions of rheological models. The CD was found to have no effect on the miscibility of low-BC ZN-LLDPE and m-LLDPE blends with linear HDPE, and both blends were miscible at all compositions. Increasing the branch content (BC = 42.0 CH₃/1000 C) resulted in an increased immiscibility of m-LLDPE-rich blends with linear HDPE. The rheology of immiscible blends suggests a layered morphology and agreement with Bousmina-Palierne-Utracki's and Lin's models was obtained with slip parameters k = 2.85 × 10^-5 and λ = 0.72, respectively.