Slit-rheometry-based characterization of the flow behavior of diluted polymer melts

Polymer melts that are diluted, that is, to which low-molecular-weight diluents have deliberately been added to modify them, have attracted growing interest due to their ability to significantly reduce melt viscosity, thereby improving processability and enhancing extrusion efficiency. We present a novel experimental setup based on slit rheometry that integrates a slit rheometer with a single-screw extruder, a gear pump, and a high-pressure liquid chromatography pump for diluent injection. A distinctive feature of this setup is its adjustable diluent injection point, which allows systematic investigation of the impact of injection location on in-line mixing, diluent incorporation, and the resulting rheological behavior under high-pressure processing conditions. In order to mitigate diluent evaporation or bubble nucleation, the Antoine equation is used to determine the pressure under which the setup operates. Experimental results demonstrated that adding n-decane to high-density polyethylene substantially reduced viscosity, with direct injection into the extruder yielding lower measurement variability and a higher saturation threshold than injection downstream of the melt pump. This advanced method offers a robust framework for determining rheological properties of diluted melts to enhance process design and optimization.