Polymers are becoming more common. They have many positive properties such as ease of use and low specific weight, but negative properties such as poorer strength and rigidity limit their areas of application. One of the solutions where the negative properties can be improved are composites. With a combination of two or more components, we can even achieve the magnetism and electrical conductivity of polymers. There is a growing use of highly-filled composites, which usually consist of a polymer matrix and a filler. Their use has great potential, but rheological behavior can be different than that of primary polymer. To better understand this behavior, amplitude, frequency and viscosity measurements were performed on a composite of glass beads in a polypropylene matrix. The test results were then compared with theoretical calculations of relative viscosity. We found that the viscosity of the composite increases with increasing filler concentration and the Newtonian plateau shifts to lower shear stress values. Through frequency tests, we found that samples with higher filler concentration behave less depending on the viscous part and more on the elastic part of the material. Broken glass particles were observed on samples with larger filler concentrations. We came to the conclusion that we can not describe the whole concentration range with one model, however we can determine which model best describes defined concentration.
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