Polypropylene packaging waste has been recycled into filaments for 3D printing as the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) and the Bremen University of Applied Sciences (HSB) join forces.
Reportedly, plastic waste has tripled across Germany in the last thirty years, with household plastic waste said to have surged by 3.5 million metric tons between 1994 and 2023. Packaging waste is thought to be a ‘major contributor’ to this surge.
However, post-consumer waste is described by Fraunhofer as ‘highly heterogeneous’ and ‘dirty’, which makes it harder to recycle than plastic residue from industrial production. As such, the company has joined forces with HSB to implement recyclate from private households into additive manufacturing.
During a feasibility study, HSB and Fraunhofer IFAM sourced polypropylene output from a sorting plant for packaging waste. HSB’s Laboratories for Circular Economy ensured that the waste was ground up, washed, and separated from unsuitable materials using float-sink-separation and near-infrared technology.
“Since the waste is supposed to be recycled for use in 3D printing, it has to meet very stringent requirements for aspects such as purity, shape and size,” explains Dr. Dirk Godlinski, a project manager in the Composite Technology working group at Fraunhofer IFAM.
Next the waste was ground again until it reached the desired grain size, and subsequently dried. According to Fraunhofer, this process exceeded purity levels of 99.8%.
“In the project, we produced homogeneous polypropylene from the prepared waste,” Godlinski continues. “This is a versatile form of plastic that is durable, resistant to breaking and relatively flexible.”
Recycled polypropylene flakes were then processed in an industrial extruder at Fraunhofer IFAM; different extruder screw geometries were used to combine the material, which was subsequently melted at over 200°C and extruded.
“The expertise consists in precisely adjusting the various mechanical screws, temperatures, pressures and speeds along the production process so the final product is homogeneous polypropylene,” says Godlinski.
In order to be further processed for 3D printing, a strand of plastic must apparently be ‘round and consistent in diameter over its entire length, with a smooth surface’.
So far, a grey plastic strand, about two millimetres thick, has been used directly as a filament in a commercial 3D printer. Among the first successfully printed packaging components are caps.
Following the results of the feasibility study, Fraunhofer IFAM and HSB are working to optimize the production process and generating new ideas for follow-up projects. In Godlinski’s view, the plastics can be refined further by introducing glass fibres during compounding, among other measures; this would unlock further product applications for the 3D printed plastic, including aviation and automotive components.
Additionally, the Packaging and Packaging Waste Regulation mandates that most industries’ packaging must contain between 10% and 35% recyclate by 2030, depending on the plastic type and product; these increase to anywhere between 25% and 65% by 2035. Fraunhofer and HSB hope their work will contribute towards these goals.
“Increasing the demand for recycled materials is important,” says Dr. Silke Eckardt, a professor focusing on sustainable energy systems and resource efficiency at HSB. “Especially with regard to climate change, we need to think about resource efficiency. The circular economy is becoming more and more important.”
Godlinski adds: “The more waste we reuse and recycle, the more energy and resources we can conserve.”
Late last year, researchers from the University of Birmingham turned lipoic acid, a naturally occurring fatty acid molecule, into a photocurable resin for 3D printing. At end-of-life, this material can reportedly be broken down into its constituent parts, recycled, and reprinted.
A team of scientists from the University of Washington has also 3D-printed a ‘compostable’ packaging material made from coffee grounds, mushroom spores, and mycelium, intended a replacement for polystyrene dunnage. Although the requirement for uniform granularity in the coffee grounds is set to pose challenges for scaling the solution, the team plans to experiment with other recycled materials going forward.
In another project, the Fraunhofer Institute for Process Engineering and Packaging IVV has created folding boxes, trays, and other paper-based packaging made from peatland plants; this hopes to tackle Germany’s ‘very high’ wood import rate, lessen reliance on chemical pulping, and improve the mechanical properties of packs made from other straw pulps like bamboo.
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