TECHNOLOGY | RECYCLING LINES
Global Application Owner Recycling. “In the first stage, a twin-screw extruder is fed with the plastics scrap and prepares the starting material so that the degassed melt can be filtered through a 100-300 micron filter – depending on the technical specifi- cations of the future product. Depending on the planned use of the material to be produced, either a pelletising system is arranged downstream from the ZE extruder, or the cleaned melt is directly transferred to the second stage, a compounding extruder. This extruder is used for controlled material upcycling by incorporating fillers and reinforcing agents, additives, stabilisers and dye.” For ground material with an apparent density of below 0.25 kg/l, the EdelweissCompounding technology can be complemented by an upstream compacting stage. The company adds that the “fluffier” the input material, the more important is the use of a compactor cutter in order to heat, dry and agglomerate the sheet and film scraps to facilitate their subsequent processing in the twin-screw extruder.
Optimum degassing solutions are also available for solvent-based recycling. “The solvent-based process is an interesting alternative especially for
recycling composite materials that cannot be separated mechanically,” says Keilbach. “Solvents are used to separate polymers from plastics composites or plastics compounds. However, the solvent has to be removed again afterwards. With the ZE BluePower twin-screw extruder, the rotating movement of its screws creates a large and permanently renewed melt surface, from which trapped volatile matter can escape more easily. Through openings in the housing that are con- nected to a vacuum, the solvents are removed from the process. The solvent removal is carried out in different pressure stages. The contaminated solvents are evaporated and subsequently con- densed before they can be reused.” He continues: “The exact process characteristics
are again determined by the required properties of the polymer produced. To reduce the original 30% residual solvent content in the material to 2%, for example, a twin-screw extruder will be sufficient. However, if purity levels in the ppm range are required, a two-stage cascade configuration is recommended. KraussMaffei Extrusion implements this cascade solution by using a combination of a single-screw extruder with a twin-screw extruder.
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