Continuous Chemical Recycling of Polystyrene with a Twin – Screw Extruder

The increasing scarcity of resources and growing environmental awareness require higher recycling rates for plastic waste. Common techniques to do that are mechanical recycling, thermal recycling and chemical recycling, which is also called feedstock recycling. From all three techniques, chemical recycling is the only one which can produce new materials that correspond to the quality of conventional virgin material. However, the technique is limited to suitable polymers, e.g. polystyrene, which can be depolymerised at elevated temperatures. For an efficient industrial scale-up, a continuous process is desirable. In our work, we present such a continuous process for the recycling of polystyrene from post-industrial waste. A co-rotating, tightly intermeshing twin-screw extruder in high-temperature design is used together with a vacuum separation system with three degassing openings. By determining a stable process point a continuous depolymerisation of polystyrene is technically realised.