Issue link: https://www.e-digitaleditions.com/i/1325722
36 / January 2021 powderbulk.com PROCESSING EXPANDABLE POLYSTYRENE IN A PLOW MIXER Mixing expandable polystyrene (polystyrene beads) with additives gives the polystyrene beads particular characteristics that are useful to a wide variety of industries. However, the additives mixed with the polystyrene beads are often needed in very small quantities. This article describes a plow-type mixer and how the mixer is used to process polystyrene beads and additives. Thomas Wegener and Martin Schmitz, Lödige Process Technology studies, the global demand for polystyrene beads is expected to increase in years ahead. 2 Polystyrene foam is manufactured using a poly merization process that involves turning liquidform styrene monomer into polymers, referred to in this article as polystyrene beads. The blowing agent pen tane is added during the polymerization process, and this prefoam step results in the polystyrene beads, as shown in Figure 2, which can then be turned into foam. After polymerization, the beads are fractioned to achieve a uniform bead size. The fractioned pen tanefilled beads are then put into a customerspecific mold where they'll be transformed into polystyrene foam by applying pressure and water vapor at a tem perature of around 212°F (100°C). During this process, the blowing agent evaporates and the compact poly styrene beads expand up to 50 times their original volume, at which point they're considered polystyrene foam. The polystyrene beads can be manufactured into panels, as shown in Figure 3, blocks, and more complex shapes based on the customer's needs. E xpanded polystyrene (polystyrene foam) is a lightweight, robust, closedcell bulk material created from expandable polystyrene (polystyrene beads). The resulting hard foam product (also called EPS) is used in industries that range from construc tion and building to packaging and sporting goods. Depending on the intended purpose, polystyrene foam may need special characteristics such as antistatic or flameretardant properties or to be a specific color. These characteristics can be achieved by introducing additives, from one to multiple different additives, often in very small quantities, to the polystyrene beads before they are expanded. A horizontal plowtype mixer, as shown in Figure 1, has proved to be ideal for this complex process engineering task. Polystyrene foam was invented nearly 70 years ago. BASF Group first presented the material in 1952 under the brand name "Styropor" at the plastics fair in Düsseldorf, Germany. Today, polystyrene foam is used throughout the world. In 2018, 10.3 million tons of the material were produced. 1 According to current market FIGURE 1 Plow mixers for continuous operation can be specially designed for high throughput rates. FIGURE 2 Polystyrene beads need to be fractioned before being combined with additives.