Measuring viscosity of polyethylene blends using a rotational rheometer

Polyethylene (PE) is one of the most important and widely used polymer in packaging industry, film and tube forming technology [1]. Knowing the properties of polymer blends and the characterization of their rheological behavior is useful for industrial processes. For that very reason in our research PE blends were prepared and characterized by rheological method to find out the differences between the blends and the base materials. The base materials were TIPELIN FA 381-10 (high-density polyethylene, HDPE) and TIPOLEN FB 243-51 (low-density polyethylene, LDPE). The PE blends were made in the following proportions: 80/20, 60/40, 40/60 and 20/80. The first numbers mean the FA content percentage in the blend, while the second numbers mean the FB content percentage. Viscosity of the polymer melts were measured by rotational rheometer at low shear rate and the effect of temperature on viscosity were also measured. The structure viscous behavior of the polymer melt was confirmed, as the physical structure of the polymeric chain changes in flow. The fact that the number and the structure of the branches influence viscosity was revealed. FA material (HDPE) has the highest viscosity, while FB (LDPE) has the least. The blends show a good correlation between the two limits, although the complex viscosity does not show linear behavior in FA material content. The least viscosity was measured at 20% FA content. The modulus values plummet with temperature. The polydispersity index is 2.2 for FA material at 230°C. The temperature dependence of viscosity was revealed for blend (40-60). Moreover the activation energy was calculated at three frequencies. The fact that the activation energy decreases in function of angular frequency was demonstrated.