Polymer composites with magnetic particles are mixtures composed of thermoplastics with added additives and various powders with magnetic properties. They are used to make bonded magnets, with the polymer acting as a binder that binds the magnetic particles together in the desired shape. In order to ensure the best possible magnetic properties, the aim is to maximize the proportion of magnetic powder in such materials. As the content of filler increases, the viscosity increases, quality melt injection molding becomes more and more challenging and cooled finished products become increasingly brittle.
In this work, we analyzed the viscosity of highly filled polypropylene with different proportions of strontium ferrite powder. From the literature, we selected different models for predicting shear-dependent viscosity, depending on the proportion of solid particles. We also compared the experimentally obtained values with calculations and chose the model that best describes the discussed materials.
We found that the viscosity increases with increasing ferrite content. The limit of the first Newtonian viscosity range moves to lower shear rates. The deviations of the models from the measurements are highly dependent on the shear rate at which the measurements were made. At shear rate 1,06 1/s, the viscosity is best predicted by the Krieger Doughtery model and at 10,6 1/s by the Chong model.
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