High Speed Extrusion of amorphous Polymers using the Example of Polycarbonate (PC) and Polymethylmethacrylate (PMMA)

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New developments in the field of single screw plastification are characterised by continually endeavouring to raise the process' economic efficiency and to simultaneously guarantee a high melt quality. As a rule, this signifies an increase in the throughput for the same size of machine. The screw diameter related throughput has grown significantly in the past decades. Grooved bushes, more powerful drives and the use of optimised screw geometries have substantially contributed to this development. But this approach has come to its limits.A further increase in the throughput of a machine (without increasing the screw diameter) can be obtained by increasing the screw's rotational speed. Shifting the energy input from the torque to the rotational speed also enables direct, gearless drives to be used so that gearbox losses can be avoided. Besides this, the extruder's power consumption is lowered by means of the reduced surface area for throughput-related heat loss. The reduced size of such machines is another significant benefit. Further advantages result from the smaller channel volumes since it reduces the material's residence time. This results in less material degradation and faster changes of the material and the operating point.However, the high-speed machine approach is subject to process engineering limitations. A poor hopper feed-supply of the material, a non-uniform material feed with pulsing output and too high melt temperatures are some of the aspects which must be taken into account. In particular, the melting behaviour also plays an important role owing to the extremely short residence times. Up to now most research work with reference to high screw speeds was focused on semi-crystalline thermoplastics (especially polyolefins like PE and PP). Hence most findings result from the specific properties of these materials.So far only a few results exist for amorphous thermoplastics. Due to a different structure compared to semi-crystalline thermoplastics, the processing characteristics of amorphous thermoplastics concerning solids conveying, melting and material degradation differ.The aim of this research project is to understand the process and develop design rules for processing amorphous thermoplastics by analyzing physical effects during the processing of these materials at high screw speeds (2100rpm). To this experimental investigations will be carried out. Process data will be examined as well as the mechanical and optical properties of the product (film). The extracted results will be analyzed by tightly focused simulative Methods to educe criteria to design process for the considered materials. To verify these results an optimized screw will be designed and tested with these criteria.