Key Component Extruder
In addition to the mechanical removal of foreign particles by means of melt filtration systems, thermal cleaning by diffusion plays a second key role in the extrusion process. In vacuum degassing, low-molecular components such as monomers, oligomers, solvents, reaction and decomposition products in the plastic melt are removed at high temperature in evacuated zones of the degassing extruders used. Decisive for the efficiency of vacuum degassing of polymer melts is the size of the melt surface in contact with the vacuum and its constant renewal. Usually, twin-screw and multi-screw extruders are used for this purpose.
Post-consumer waste generally has to be washed before reuse and still contains a high amount of residual moisture after the first mechanical drying. In contrast to conventional extrusion processes, with Gneuss MRS Extruders, this residual moisture does not have to be removed by drying or the like before processing. The moisture is removed from the plastic during extrusion by a vacuum system. The water also serves as a carrier medium for the removal of chemical additives such as dyes, stabilizers, acetaldehyde scavengers, carrier oils, solvents and many more.
For the use of the recycled material in contact with food or skin, the purity requirements set by food authorities such as FDA, EFSA or other local authorities apply. All organic and inorganic potential toxins must be removed, which is achieved with the MRS extruder with a high decontamination performance during the degassing phase.
For more than a decade, the Gneuss MRS Extruder has been used for the recycling of highly contaminated recycled material such as post-consumer waste, industrial waste from fibre and film production made of PET as well as other different hygroscopic polymers (e.g. polyamide) and also for polyolefins and polystyrene.
The design of the MRS extruder’s multi-screw section increases the melt surface available for degassing many times compared to conventional extrusion systems available on the market and generally requires a simple vacuum of only 25-30 mbar. For particularly demanding applications, vacuum systems up to 1 mbar specially developed for the process are also available. The high degassing capacity removes volatile impurities, oils and odours extremely effectively. Polymers with a moisture content of up to 2% can be processed directly into high-quality end products.