"We need to close loops"

In the 1980s, the slogan "jute instead of plastic" was a catchphrase, and even today, when we think of environmental protection, we think primarily of avoiding plastic. On the other hand, plastic is nowadays regarded as a multifunctional, environmentally compatible and sustainable material with a high innovation potential for technologies of sustainable development. How does that fit together?

In fact, there are studies that say that reusable plastic bags, i.e. the thick plastic bags that are widely used in Germany and have now been banned by legislation, may well be more sustainable than jute or cotton bags, depending on how often they are reused, because a lot of resources such as water or land are used to grow some plants. That's where the legislation overshoots the mark a bit. What makes more sense and is more targeted is the ban on single-use plastic cutlery. Here, too, the solution is not wooden cutlery, but always reusable.

Ultimately, plastics are indispensable today. In medical technology, they guarantee hygiene and sterility. But even electronic applications such as our cell phones or laptops - all the things we take for granted every day and cannot imagine a sustainable future without - are based on plastics, whether for insulating cables, in plug connections or housings. In addition, there are many non-visible parts made of plastic, which allow a high level of functional integration and thus the minimization of installation space in such applications. But in the construction industry, too, plastic foams play a huge role in the energy insulation and refurbishment of buildings, so that less energy is lost during the use phase, and are clearly among the sustainable solutions we need.

Packaging is a good example of the ambivalence of the issue: On the one hand, they allow food to last longer and stay fresh; on the other hand, they naturally create packaging waste. The most important thing here is that people around the world are sensitized to handle packaging properly, even after the first phase of life, so that plastic does not end up in the environment.

In other words, to ensure that plastic products do not become worthless waste, but rather valuable materials with no harmful effects on the environment and climate, we have to "think in circles," that is, give these products more than just one life and recycle them?

Exactly. We need to use plastics sensibly, which means, for example, creating reusable systems for packaging, as has already happened with the to-go cup, for example. We need to promote such developments even more. Legislation still stands in our way to some extent, because it's not so easy to bring our lunch box to the sausage counter. But we can do a lot in terms of multiple use and reusable packaging and must not regard plastics as cheap or disposable products, but as an important raw material and material.

It is not for nothing that there is the waste hierarchy propagated in the EU, in which the first priority is to avoid waste, i.e. the question: Do I really need the mini bags of gummy bears? Then comes reuse, i.e. the aforementioned to-go cup. Then comes recycling, and finally energy/thermal recovery and disposal of the waste, i.e. landfilling, which in Germany, for example, already accounts for only a negligible percentage.

What else needs to be considered with plastics in the circular economy?

We need to think about other forms of use and business models. If we stop putting a drill on our shelves that we use to drill three holes once a year and access the drill in the neighborhood tool shed, such a machine can be designed to be more robust, because there is then only one resource for many people, which can of course be put to better use. There we have a lot of upward potential also in the design, in order to be able to use equipment more frequently again and also to recycle it at the end. In the case of automobiles, for example, this plays an important role: We not only have to think about how we can assemble the car so that it fulfills its function, but also how we can disassemble the parts so that we can recover the individual raw materials, i.e., reuse or recycle them. We already have many technical solutions today, but they can only be implemented in conjunction with the right business models.

What part can we as consumers play in the circular economy?

Avoid, reuse and - as mundane as it sounds - separate the waste properly, for example separating the cardboard label from the yogurt pot and tearing off the aluminum foil completely at the top: Then I have three pure recyclables that I can recycle. If the lid and the cardboard label are still attached, the sorting system recognizes the individual recyclables as pure, depending on how you look at it, even though there are several components involved. So we have to take the time to take apart such a yogurt cup or return deposit bottles to the deposit systems. The PET system shows that if you create a single-sort recyclable stream, it can be recycled bottle-to-bottle. And this works because the right incentives are set.

That means we have to close cycles and establish more and more, but in the end we still end up with products that can no longer be recycled. If we then also use the high energy content that these materials contain, then it makes perfect sense. In addition, biodegradable plastics allow for another recycling route: composting.

You are working intensively on such plastics, known as biopolymers, both at the Technical University of Ilmenau and at the Thuringian Institute for Textile and Plastics Research (TITK).

Yes, although we also have to differentiate here: On the one hand, we have biobased polymers, which are not biodegradable but also made to last forever, but also biobased, biodegradable polymers. But there are also petrochemical-based polymers that are biodegradable. And then there is the large group that is primarily in use today, the petrochemical-based polymers that are not biodegradable. We are looking at all groups because it can make sense for some products to be either biobased, biodegradable or durable. At TITK, we have been working for a long time with cellulose and cellulose fibers, which hold immense potential for textile applications, for example, because cotton is a difficult product in terms of life cycle assessment: it requires a lot of water and a lot of land.

In a current project, you are also looking at how to avoid rejects in injection molding processes when manufacturing plastic components. What needs to be considered in the production and processing of plastics so that the corresponding processes are as energy-saving and resource-efficient as possible?

Most plastics processing operations involve processes that manufacture products in large quantities. Here, it is important to further reduce reject rates. This is the background to our project, in which we are looking at being able to correctly assign defects that occur during injection molding using an integrated sensor system consisting of an optical camera, a thermal imaging camera and a load cell. A second AI algorithm will then be used to readjust the machine accordingly so that these rejects no longer occur. We are also currently working on the use of artificial intelligence in sustainable joining processes in the new ProKI-Ilmenau Transfer Center together with other groups  at the TU Ilmenau under the leadership of the Mechanical Engineering Group.

Another field of research you are involved in is aimed at using plastics, so-called fiber composites, in the automotive sector, i.e. for automotive components. What are the advantages of plastics here and how can such lightweight components be used for sustainable mobility?

In contrast to thermoplastic processing methods such as injection molding and extrusion, lightweight construction is still comparatively young. There is still a lot of work to be done in the area of processes suitable for large-scale production, but also in terms of understanding materials. Lightweight construction is one of the key technologies in Germany and is therefore a very exciting field for us. Within the Thuringia Mobility Innovation Center, we have established, among other things, an innovative process for the production of continuous fiber-reinforced plastics, which is intended to fill precisely this gap and has something to do directly with sustainability: Wherever lightweight parts are found in moving applications, energy is saved during the use phase. In the case of automobiles, I need less energy to move my vehicle or can add other assistance systems without the vehicle becoming too heavy - and thus save either fuel or electricity.

What material, application-oriented or process engineering challenges still need to be overcome in the coming years so that we can really talk about materials of the future when it comes to plastics?

With regard to the plastics with which we consumers are in daily contact, it is certainly a question of recycling technologies, i.e. chemical recycling could be used even more intensively. And it's a question of material flow management. Mattresses, for example, are already collected in a reasonably coordinated way, but we could do even better there in terms of feeding large recycling plants with uniform raw materials. Getting a handle on the heterogeneity of material flows and processing them is certainly the biggest challenge.

Another challenge is multi-material systems, which can be advantageous in lightweight construction in the use phase, for example, but are again a major challenge in the end-of-life phase: How do I separate these materials from one another? Where does it make sense to use a multi-material system because it saves a lot of energy in the use phase? And where does it not make sense, because in the end a lot of energy has to be put into loosening connections again? This is where the issue of dismantling plays a big role, so that we can recycle better.

One example is wind turbines and the recycling of rotor blades. Many are already thinking: How do we get the blades apart so that we can reuse the materials that are bound up in them? In the medium and long term, there will be ways to make these bonds switchable, for example, and to separate the polymer from the fibers again. There are already some research approaches in this area.

The topic of the circular economy is also to be increasingly incorporated into teaching at the TU Ilmenau. What exactly is planned here?

The topic of sustainability is already firmly anchored in many subject areas. We are currently planning a lecture series in the summer semester of 2023 to look at the topic of the circular economy not only from the point of view of the materials glass, metal and plastic, but also from the product point of view, i.e. using the example of product design, vehicle and electrical engineering, but also through the lens of economists who will talk about specific incentive systems, business models and communication in this context. Because all of this is necessary to bring circular products into circulation. In the lecture series we bundle all these topics in an interdisciplinary and interactive way. That means discussions are very welcome.

We are interested in what factual basis the students bring with them and what facts we ourselves can contribute. After all, the whole thing is also an emotional discussion to a certain extent. We can't present all the solutions for a sustainable future to the students, but we can give them the tools and show them methodologies so that they can solve the problems they encounter themselves.

Personal details:

After earning his doctorate at RWTH Aachen University and working in industry for several years, Prof. Florian Puch has been head of the Plastics Technology Group at TU Ilmenau since 2021 and is scientific director at the Thuringian Institute for Textile and Plastics Research (TITK) in Rudolstadt, an affiliated institute of TU Ilmenau. His research and teaching activities focus on the functionalization of plastics and the conception and realization of novel machine systems for plastics processing. At the Thuringian Innovation Center Mobility (ThIMo) at the TU Ilmenau, Prof. Puch is responsible for the key competence area "Plastics Technology and Lightweight Construction". The focus here is on technologies for manufacturing and recycling fiber-reinforced plastics for the automotive industry.

Materials in the circular economy and industry, especially plastics, will also be the topic of the Thuringian Materials Day on March 14, 2023 at the TU Ilmenau.