Automated Mixer optimization for physical extrusion foaming

• Applicant: Professor Dr.-Ing. Christian Bonten
• Subject Area: Plastics Engineering
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441921604

The physical foaming of plastics is an established process for the production of lightweight, well-insulating materials with a cellular structure. By introducing gas into a plastic matrix, properties such as low density, high mechanical damping and good insulating properties can be specifically con-trolled. Foamed plastics play a particularly important role in the construction and transportation industries, as they enable material savings and weight reduction. The most common variants are thermoplastic foams, which are particularly attractive due to their versatility and recyclability. They are usually produced by extrusion, whereby blowing agents such as nitrogen or carbon dioxide are evenly introduced into the hot plastic melt by means of mixers at the end of the screw. A controlled process sequence is crucial for the quality of the foam: As the foam exits the nozzle the pressure drops abruptly, causing the blowing agent to expand, and create the desired cell structure. Parameters such as temperature, pressure and blowing agent concentration influence the cell size distribution and the homogeneity of the foam. A high viscosity of the plastic melt leads to smaller, more stable bubbles with high compressive strength. However, if the viscosity is too high, bubble growth can be hindered. Too low a viscosity, on the other hand, leads to unstable structures with larger cavities. A little researched, but decisive factor is the geometry of the mixer. It significantly influences the distribution of the blowing agent in the melt and thus the quality of the resulting foam. While the control of temperature, pressure and blowing agent supply has already been well researched, there have been few systematic studies on the interactions between mixer design and bubble formation. A better understanding of these relationships will significantly improve the efficiency of the foaming process and optimize the quality of the products.

• DFG Programme: Research Grants