Implications of melt compatibility/incompatibility on thermal and mechanical properties of metallocene and Ziegler-Natta linear low density polyethylene (LLDPE) blends with high density polyethylene (HDPE): Influence of composition distribution and branch content of LLDPE

In this paper, the implications of melt compatibility on thermal and solid-state properties of linear low density polyethylene/high density polyethylene (LLDPE/HDPE) blends were assessed with respect to the effect of composition distribution (CD) and branch content (BC). The effect of CD was studied by melt blending a metallocene (m-LLDPE) and a Ziegler-Natta (ZN) LLDPE with the same HDPE at 190°C. Similarly, the effect of BC was examined. In both cases, resins were paired to study one molecular variable at a time. Thermal and solid-state properties were measured in a differential scanning calorimeter and in an Instron mechanical testing instrument, respectively. The low-BC m-LLDPE (BC = 14.5 CH₃/1000 C) blends with HDPE were compatible at all compositions: rheological, thermal and some mechanical properties followed additivity rules. For incompatible high-BC (42.0 CH₃/1000 C) m-LLDPE-rich blends, elongation at break and work of rupture showed synergistic effects, while modulus was lower than predictions of linear additivity. The CD of LLDPE showed no significant effect on thermal properties, elongation at break or work of rupture; however, it resulted in low moduli for ZN-LLDPE blends with HDPE. For miscible blends, no effect for BC or CD of LLDPE was observed. The BC of LLDPE has, in general, a stronger influence on melt and solid-state properties of blends than the CD.