THE ART OF RECYCLING

Whether it's food packaging, clothing, hygiene articles or coffee-to-go cups - the list of everyday objects made of plastic is long. Since the beginning of plastic use, the annual production volume has increased exponentially. Whereas in 1950 it was around 1.5 million metric tons, today the global average is around 407 million metric tons per year. A 270-fold increase in plastic production within 70 years.

Yet only just under 20 percent of the plastics consumed annually in Germany today are currently recycled. About half is stored in long-life products, the other half appears as waste, of which in turn less than 50 percent is actually recycled and not used for energy, i.e. incinerated. Globally, the recycling percentage is even lower. Large portions of the plastic waste of many countries end up in landfills that are not always operated according to modern standards. True to the principle of "out of sight, out of mind," a lot of waste is still thrown away. The result: many developing countries are drowning in mountains of plastic waste, as plastic is colloquially known. Plastic is found in large quantities in cities, on land surfaces, in rivers and in our oceans worldwide. Over time, the plastic decomposes into microplastics with risks for humans and the environment.

At KIT, several projects deal with the topic of plastic recycling in order to cope with the global waste problem.

Tracer-based sorting technology for packaging, plastics and other materials

The company Polysecure GmbH is working together with KIT on new ways, in particular, to sort different plastics using fluorescent markers: small inorganic crystals that are excited to fluorescence by lasers or LEDs and thus made detectable. "We need to enable better sorting as the basis for an efficient and sustainable circular economy. Plastics today are sorted only by the dominant main polymer, but not by the numerous subclasses and uses of plastic packaging," says Jochen Moesslein, CEO and founder of Polysecure, describing the problem. Consequently, no distinction can be made between food packaging, motor oil canisters or housing lids. As a result of this mixing, plastics can no longer be used for their original purpose during recycling. Food packaging, for example, then becomes a dishwashing liquid bottle, which in turn becomes a park bench. Reuse for the same purpose is thus limited.

Moesslein explains "Plastics are only partially recycled today. The plastics themselves are less of a problem, because they could be remelted several times with little energy input. The problem lies at the beginning, after collection. The waste streams would first have to be sorted much more precisely and in a way that is more suitable for recycling." With the tracer-based sorting technology (TBS), the Freiburg-based company, together with KIT, has developed a process to precisely sort such waste streams into freely definable fractions. In simple terms, packaging would be marked with fluorescent markers (tracers) already during production. These can later be excited to fluorescence in the sorting plant by a type of light barrier with laser or LEDs. The corresponding plastic parts can thus be better differentiated and sorted. Illustrated, the TBS approach is thus a kind of machine letter sorting for plastics recycling. The amount of marker required per package is in the range of a few micrograms and therefore does not represent a significant cost factor. The markers can be applied either by incorporating them into the printing ink applied to the packaging or label, or by incorporating them into the plastics themselves. In addition to article sorting, the latter also has advantages for flake sorting after the packaging has been shredded. Another advantage of the process is that the detection quality of the markers is very high, because deformation, dusting or geometry have no effect on their effectiveness. Compared to other technologies, TBS technology can therefore also be used to mark and sort small, flexible or non-printed packages.

Polysecure has already been able to prove that the reliable sorting of articles and materials according to specified materials works. They have built the world's first TBS machine for separating PVC flakes containing glass fibers and successfully validated it together with an industrial partner. "Our goal now is to build a pilot sorting plant that can further develop the technology and transfer it to packaging, textiles and shredded material from vehicles, white goods and more. We need to demonstrate the feasibility and economic viability of our innovative process to key stakeholders so that the recycling targets demanded by policymakers can be achieved," says Moesslein, describing the next step.

Pyrolysis for Chemical Recycling of Industrial Plastics

The fact that the need for action does not only apply to the packaging sector is also shown by the research and development activities on the chemical recycling of mixed plastics at KIT. "In addition to packaging, there are numerous other areas of application to which about 70 percent of the plastics in circulation can be attributed and most of which are not yet recycled today. From mattress foams to insulating materials in the construction sector to electrical and electronic equipment or automotive components, to name just a few examples," says Prof. Dr. Dieter Stapf, head of the Institute of Technical Chemistry (ITC) at KIT.

At the ITC, the focus is on process engineering research to close plastic loops. "The big challenge here is to turn complex products and their contaminated waste back into raw materials for new chemical products and plastics. As a rule, at the end of the life cycle of many products, plastics are not present as pure, separable polymers. They are mixtures, for example plastics mixed with biomass, metal parts, color pigments or flame retardants. Such highly functionalized, combined, mixed or heavily contaminated plastics are often not easy to separate mechanically, and in some cases cannot even be melted," says Prof. Stapf, describing the basic problem. Therefore, the waste must be chemically processed to make it usable again as a petroleum substitute. "We need to recycle much more of the valuable and energy-intensive plastics to protect the climate and the environment. Here we need new processes that are capable of reprocessing these polluted mixtures into raw materials to complement mechanical recycling," Prof. Stapf added.

One solution offered by the researchers at the ITC is to use pyrolysis to break down the plastics that cannot be recycled today back into basic chemical building blocks and to separate out impurities. "At our experimental plant, we work with real and thus representative waste and produce sample quantities of the secondary raw materials. At the same time, our basic process engineering research on this provides the know-how for technology development and scale-up, which are of interest to cooperation partners," says Prof. Stapf. The ITC's research group maintains various collaborations with companies from the waste management sector, the chemical industry or with plastics processing companies in order to investigate a range of plastics and enable innovations.

The use of plastics has become established over decades and will be difficult to imagine without. This makes it all the more important to enable the more efficient separation and further processing of plastics and thus also to strengthen the sustainable circular economy. A holistic approach is essential here, because collecting packaging in the yellow bag alone will not reduce today's mountains of waste and the associated climate gas emissions.