In view of the constantly growing amount of plastic waste in German private households, scientists at Bremen University of Applied Sciences and the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) are investigating how post-consumer plastics from the Yellow Bag can be processed for 3D printing. The aim is to produce high-purity filament for additive manufacturing from heavily contaminated packaging waste.
“However, it is much more difficult to recycle post-consumer waste than plastic waste from production, for example,” explains Dr. Silke Eckardt, Professor of Sustainable Energy Systems and Resource Efficiency at Bremen University of Applied Sciences.
In a joint project, polypropylene was first removed from a lightweight packaging sorting plant and then processed in several cleaning and separation steps. Using the float-sink method, near-infrared analysis and mechanical shredding, the researchers achieved a material purity of over 99.8 percent.
“As the waste is to be used as a recyclate in 3D printing, it has to meet particularly high requirements in terms of purity, shape and size,” explains Dr. Dirk Godlinski, project manager in the Composite Technology working group at Fraunhofer IFAM.
This is where the Fraunhofer IFAM took over: “In the project, we produced homogeneous polypropylene from the processed waste,” says Dirk Godlinski. “This is a versatile plastic that is durable, break-resistant and relatively flexible.”
The material was brought together in an industrial extruder, melted at over 200 degrees and extruded into a two-millimetre-thick plastic strand that could be used directly in 3D printing.
“The expertise lies in adjusting the various mechanical screws, temperatures, pressures and speeds throughout the manufacturing process so that homogeneous polypropylene is produced in the end,” explains Godlinski. For example, for further processing in 3D printing, the diameter of the strand must be round and constant over its entire length and the surface must be smooth.
The feasibility study has been completed and the process is currently being further optimized. One possible further development involves the addition of additives such as glass fibers in order to specifically improve the material properties.
“It is important to increase the demand for recyclates,” Silke Eckardt is convinced. “Particularly in view of climate change, we need to think about resource efficiency. The circular economy is becoming increasingly important.”
Dirk Godlinski agrees: “The more waste we recycle, the more energy and resources we save.”
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