The problems reviewed in this monograph concern single-screw plasticizing systems, which are widely used in the construction of modern extruders. The aim of the studies presented here was to streamline the process of extrusion by developing a new design of a single-screw plasticizing system of a thermoplastic extruder. As part of the studies, a model of an original extruder, W-25, was constructed, in which, the extrusion process involves the rotation of both the screw and a part of the barrel - its rotary sleeve. The results of the tests of the extruder model and the experiences gained during the experiments served as the basis for developing the design and then constructing prototype W-45 of the original extruder. The present monograph reports selected original results of research on the effectiveness of new design solutions for a screw plasticizing system of an extruder and discussions of those studies in the light of the current state of knowledge in this area.