Refurbishing the plastic recycling chain

Today, most consumables and everyday items are made from petroleum-based plastics. In Germany alone, approximately 6 million tons of plastic waste are generated every year. About half of this is mechanically recycled into new materials; the remainder is used for energy recovery. Burning this waste releases carbon dioxide, a greenhouse gas. The recycling of plastics is therefore very important from a climate and environmental protection perspective. As part of the Waste4Future flagship project, eight Fraunhofer institutes are developing new ideas and processes to significantly increase the mechanical recycling rates of plastic materials.

Many everyday products would not exist without plastics such as polyethylene, polypropylene or polystyrene, which are made from fossil raw materials. The problem is that the mechanical recycling rate of plastic materials in Germany is still too low. More plastic waste is currently incinerated than mechanically recycled into new materials. While incineration of waste harnesses its energy potential, valuable materials are lost forever. In a truly circular economy, waste would not be incinerated but would at least be reused and recycled mechanically or chemically as a priority. This not only reduces the demand for fossil resources, but also reduces carbon emissions that pollute the environment. Furthermore, the carbon in plastics will remain as an important resource used by the chemical industry. Eight Fraunhofer Institutes are pooling their expertise in the Waste4Future flagship project (see box) to develop new solutions to this challenge, from raw materials to material flow and process engineering, right up to the product life cycle Finish. The Fraunhofer Institute for Materials Recycling and Resource Strategy IWKS is coordinating the project.

Fraunhofer institutes and research units involved

---Fraunhofer Research Institution for Materials Recycling and Resource Strategies IWKS

---Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR

---Fraunhofer Institute for Ceramic Technologies and Systems IKTS

---Fraunhofer Institute for Structural Durability and System Reliability LBF

---Fraunhofer Institute for Microstructure of Materials and Systems IMWS

---Fraunhofer Institute for Optronics, System Technologies and Image Exploitation IOSB

---Fraunhofer Institute for Process Engineering and Packaging IVV

---Fraunhofer Institute for Nondestructive Testing IZFP

"Plastics are made from hydrocarbons. At the end of their useful life they are disposed of and then sorted. Low-quality plastics that pollute too much are incinerated, while high-quality plastics are sorted by color and sold as recycled material. But Recycling these valuable materials is complex depending on the type," says Dr. Gert Homm, a subproject leader and research scientist at the Fraunhofer IWKS in Arzenau. “Many packages are not even considered recyclable by sorting facilities and end up in incineration plants as residual waste. Many of today’s sensors cannot identify black plastic, and even yogurt cartons with foil lids end up being mistaken for aluminum , and then become residual waste.”

© Holger Jacoby

Andreas Keller, Research Scientist at the Waste4Future Alliance, demonstrates a demonstration model

Today’s waste, tomorrow’s valuable resources

The Waste4Future project is developing a sensor suite for sorting facilities that, among other things, can detect black waste particles. The intelligent combination of different sensors in the sensor suite, including infrared and terahertz sensors, determines the most accurate possible detection of material classification parameters as well as the degree of degradation of the sample. The degree of aging of a sample is relevant when assessing whether and how suitable it is for mechanical recycling. When something is severely damaged, it cannot be recycled mechanically, only chemically. Both properties can be identified using sensor suites. It uses sensor technology, some of which is developed in-house, to detect and cross-connect various physical properties of plastics (optical, thermal, etc.). The data collected is cross-linked and evaluated using machine learning techniques. Sensor suites used to identify waste are installed above conveyor belts in sorting facilities. Compressed air nozzles then sort the sought target materials or unwanted contaminants. Chlorinated plastics, such as polyvinyl chloride (PVC), can be a problem in chemical recycling. Chlorine levels can cause severe corrosion in the systems required for this, especially in chemical recovery. Generally speaking, the purer the plastic, the higher the quality of the recycled material.

A large amount of data is generated when the sensor detects plastic. The researchers say: “Digital twins help reduce the amount of data to essential core data and pass this into the assessment model we are developing as part of the project, thus transforming previously process-based recycling chains into material-based recycling chain.” Factors such as energy consumption and carbon footprint are taken into account in this process. A combination of innovative sorting technologies, digital twins, machine learning and assessment models dynamically adapt to specific quantities of waste the recycling routes that make the most sense from a technical, ecological and financial perspective. The assessment model calculates the environmental impact and provides information on how much energy is required to produce a ton of new plastic. Compare this energy consumption to the energy required for energy recovery. The assessment model analyzes the various options for recycling plastic to allow for a true comparison.

Those involved in the project are investigating potential mechanical (melt extrusion, solvent-based purification and fractionation) and chemical (dissolution, pyrolysis, gasification) recycling processes and testing their suitability for different compositions of plastic waste. By the end of the project in December 2024, it will be possible to compare components made of old plastic with new materials.

© Holger Jacoby

Close-up of demo model: Here sensors and compressed air nozzles are used to sort plastics of different colors and compositions

Circular economy instead of energy recovery

"A sustainable society with climate-neutral processes requires a significant adjustment of the value chain, which can only be achieved through innovation. As part of this project, we are following up on this issue to develop the best possible recycling routes as well as the best The sorting process, taking into account both financial and ecological factors, thus contributes to a significant reduction in carbon emissions compared to energy recovery and enables a high degree of recycling of carbon-containing waste,” says the physicist.