Shredding is the component of the most important techniques of mechanical recycling of polymeric materials. It is often used as one of the main preparatory processes, associated with the constitution of composite materials. This means that it is a very important and current problem to be solved in terms of technology, design, and economy, as well as environmental protection. A preparation of composite material components by shredding depends specfically on the expected degree of fineness, appropriate size distribution and desired morphology of an elementary particle. The subject of this work concerns mechanical shredding of polymeric materials in various types of mills and agglomerators. The paper presents the tests for verifying the influence of size and shapes of openings in sieves made in the shredder on selected parameters and properties of the obtained recyclate. During the shredding process, the following parameters were analysed: electricity consumption, temperature inside the shredding chamber and the temperature of the obtained recyclate. Selected properties of the obtained recyclate, such as: geometric features of the recyclate dependent on the applied sieves, bulk density and the angle of natural repose were also determined. Mouldings with a gating system, made of polypropylene, were the subject of shredding.