Process Analytics for Co-Rotating Twin Screw and Single Screw Extruders

Nowadays, process analytics is an important part in the processing of polymer materials. The sooner the properties of the polymer can be analyzed the better it is to intervene as necessary. One of the most important tasks of a compounder is mixing. To achieve the highest product quality with an excellent distribution of fillers and reinforcing materials, the quantification of the mixing ability is essential. This work deals with different measuring systems in order to study the influence of various process parameters and extruder types to determine the quality of mixing. Main attention is paid to the characterization of the distributive and dispersive mixing behavior of co-rotating twin screw and single screw extruders. In the present work, an inline fluorescence spectroscopy has been developed, which was used to characterize the distributive mixing ability of extruders. Experiments were performed using an in-line color measurement to compare both systems. The residence time distributions of different screw sections were calculated with the convolution of individual screw elements. Considering the melt temperature, the specific energy input, the fiber length reduction and the residence time in the extruder, two new dimensionless numbers were introduced. Scaleup / -down processes of different extruder series can be supported by using these indicators. Furthermore, infrared spectroscopy was used in combination with multivariate data analysis to determine the effect of individual process parameters on the reactivity of powder coatings. Secondary electron microscopy, terahertz spectroscopy and dielectric analysis were used for the characterization of metallic pigments in powder coatings and the fiber length distribution of carbon fibers in polypropylene was analyzed by an optical measurement system. The particle size distribution and fiber length reduction characterize the dispersive mixing ability of the extrusion system. Additionally, several extruder sections were calculated numerically and compared with the measurement data.