The effect of the addition of a slip agent on the rheological properties of polyethylene: off-line and in-line measurements

Abstract

Abstract The article describes an investigation into the effect of a slip agent on the rheological properties of low-density polyethylene. As a slip modifier, oleamide was used in the amounts of 0.5, 1.0, 2.0, 3.0 and 4.0 wt.%, respectively. The process of polymer modification was carried out in a twin-screw extrusion process. The effect of the slip agent on the mass flow rate index was determined. The specific plasticisation energy of the modified polymer was also assessed based on the change in the torque of a batch mixer. The assessment of the effect of the addition of oleamide on the change in the flow and viscosity curves was made using an off-line (plastometer) and an in-line (extruder rheometer) measuring technique. The rheological parameters were determined based on the Ostwald-de-Waele power law model. The operation of the plastometer was brought closer to the principles of operation of the capillary rheometer by applying variable piston loading. In in-line measurements, an extrusion head with replaceable cylindrical dies was used. Using two rheological measuring techniques made it possible to determine the low-density polyethylene viscosity variations and the values of flow power law index (n) and consistency factor (K) in a wide shear rate range.