Rheological properties of polypropylene composites with calcium carbonate under high shear rates

The rheological properties of isotactic polypropylene (iPP) and its composites with unmodified and stearic acid-modified calcium carbonate (5, 10, 20, 30 wt%) were investigated. The processability factor K of the composites was determined based on changes in the mass flow rate (MFR). The assessment of rheological properties was carried out at high shear rates, in the injection process, using a special in-line measuring head. Measurements were performed at a temperature of 230 degrees C, in the range of apparent shear rate from 19,100 to 101,900 s(-1), based on the Ostwald-de Waele power-law model. Comparative analysis of the processing and rheological characteristics, as determined with two techniques (off-line measurements and in-line measurements), has shown a diverse behaviour of polymer composites in flows (flow resistances, the behaviour of the flow and viscosity curves, the power law index), resulting from a varying fill degree, applied filler type and measuring shear rate range.