Characterization of High‐Shear Viscoelastic Properties of Polypropylene Using a Closed Cavity Rheometer

ABSTRACT This study evaluates a closed‐cavity rheometer (CCR) for rheological characterization of polypropylene (PP) and compares its performance with an open‐cavity rheometer (OCR) and capillary rheometry. Thermorheological simplicity was first confirmed using van Gurp–Palmen and Han plots, which supported time–temperature superposition (TTS) for master‐curve construction at a reference temperature of 225°C. The CCR master curve extended the accessible frequency range to approximately 1000 rad/s and enabled estimation of high‐shear‐rate viscosity through the Cox–Merz relationship. Complex viscosity from the CCR master curve agreed closely with apparent shear viscosity measured by capillary rheometry, while OCR data deviated at higher shear rates. Cross‐model fitting of CCR viscosity data also provided a reasonable estimate of zero‐shear viscosity. Direct CCR testing of PP pellets required minimal sample preparation and avoided thermal preprocessing steps that may alter material behavior. Large‐amplitude oscillatory shear (LAOS) measurements further enabled qualitative and quantitative assessment of long‐chain branching, and the results were consistent with largely linear PP behavior. In addition, a LAOS dissipation‐based parameter (1/ ϕ ) showed close agreement with capillary die‐swell ratio which indicated strong potential for rapid die‐swell screening using CCR‐based LAOS testing.