Plastic

^{Web special Fraunhofer magazine 3.2023}

Simon, six, has a decision to make: the soda can or the yogurt pot? The empty water bottle, the chocolate packaging or the tornopen chips bag? At the Fraunhofer Institute for Process Engineering and Packaging IVV booth at the Munich Science Days event, Birgit Faltermayr has lined up all kinds of trash – but what belongs in the bag for recyclable packaging, and what goes in the recycling can? Hesitantly, Simon picks up the yogurt pot and looks questioningly at the scientist. “Bingo,” Ms. Faltermayr says approvingly. And plop – the yogurt pot disappears into the bag. Easy peasy, right?

But when it comes to plastic, unfortunately nothing is simple anymore. This material’s heyday, stretching from the mid-20th century, was based entirely on one promise: that with its practically unlimited possibilities in terms of shape and properties, and its durability, low weight and cheap price, plastic would make a lot of things simpler, lighter and cheaper. For decades, it seemed as though this promise could be fulfilled unconditionally. The world became more colorful, products became cheaper and safer, and industrial processes became more efficient. Since the 1950s, plastic production has grown by an average of 8.4 percent per year; over 8 billion tons of plastic have now been produced globally.

However, the issue of what happened to the material after it was used went overlooked. In many areas of the economy, people failed to adequately consider end-of-life models for plastics, as well as the carbon footprint of plastics and composite materials. The environmental consequences have been devastating: One in twenty tons of petroleum are used for plastic production; this industry accounts for 4.5 percent of global greenhouse gas emissions. What’s more, the material’s recyclability has been ignored in favor of disposable convenience. Since the start of the plastic boom, almost 5 billion tons of waste plastic have been introduced into the environment and accumulated in open landfills.

The United Nations Environmental Assembly wants to introduce an international treaty to mitigate plastic pollution globally; the completion of the negotiations and entry into effect are set to take place by the end of 2024. The UN environmental organization UNEP has now lit a light at the end of the tunnel, and it’s sparking hope – a study published in mid-May indicates that it will be possible to reduce global plastic pollution by over 80 percent by 2040. But how?

“The plastics sector is being transformed at a fundamental level,” states Prof. Sebastian Scholz, director of the Fraunhofer Plastics Technology Center Oberlausitz at the Fraunhofer Institute for Machine Tools and Forming Technology IWU. This shift is not just limited to the industry – it affects every individual. After all, when we heard the word “plastic,” we mainly think of single-use products and waste packaging, but there’s a lot more to plastics than just that. And they are everywhere: in our clothes and cosmetics, in cars, airplanes, trains, in the casing of electric devices and in buildings. Even space debris, which is increasing every day, is mostly made from plastic, as many plastics are used to build satellites and rockets. “It’s vital that we develop techniques to help make the production and use of plastic more sustainable,” says Prof. Scholz.

There is an important question to be researched here: To what extent can fossil-based plastics be completely or partially replaced with biobased materials, without them losing their desired properties? As part of the LaNDER3 network at the Zittau/Goerlitz University of Applied Sciences, several Fraunhofer institutes are working together with numerous companies to conduct research into replacing glass fibers in synthetic fiber-reinforced plastics with natural fibers. The aim is to retain the advantages of glass-reinforced polymer composites (GFRPs) – a high rate of mechanical stability and resistance, as well as low levels of corrosion and low production costs – in these natural fiber-reinforced polymer composites (NFRCs). For example, the use of tow, a byproduct of hemp and flax fiber production, has been tested in manufacturing interior paneling for trains – this material is inexpensive and available in sufficient quantities. “The NFRC components can rival GFRPs in terms of robustness, flow properties and fire resistance,” says Prof. Scholz.

To prevent the solution to this problem from just causing another issue, sustainability needs to be considered right from the outset when selecting new raw materials for the plastics of tomorrow. Because if agricultural products were the only resources meeting Germany’s enormous appetite for plastic, they would no longer be used for food. Plastics can never be allowed to compete with food. In the EnviroPlast project, researchers from the Fraunhofer Plastics Technology Center Oberlausitz are investigating the use of fibrous residual materials, such as straw, waste wood from lumber mills and other organic waste, as fillers. “We are experimenting with materials and playing with processes to develop plastics where over 50 percent of the fillers consist of residual materials,” Prof. Scholz explains. “That will decrease production costs, increase the level of sustainability in manufacturing – and capture CO2 for many years, as these components are generally in use for decades.”
 

At the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Dr. Roland Klein is working on the DuroBast project together with partners from science and industry to find a wider range of application areas for bast fibers in NFRCs. “With NFRCs, there is a risk that they will be saturated with moisture from the environment if the component becomes damaged, for example. Not only can this degrade the mechanical properties, but it could also encourage the growth of microbes,” explains Dr. Klein. In order to counteract this absorption of moisture, the research team at Fraunhofer LBF uses a type of pretreatment process to fill in the spaces between the fibers with a biobased plastic. It is only in the second step that the project partners combine the reinforcing material with molten thermoplastic and press it into a moldable semi-finished product. Initial tests have shown that the fiber pretreatment process results in a more robust product. “Improving the mechanical properties of this NFRC means that we will ultimately need less material,” Dr. Klein says optimistically. This would also decrease the ecological footprint involved.

With coatings such as proteins or waxes, this packaging will even be able to protect particularly perishable foods like meat and dairy products and baked goods. Dr. Stephan Kabasci, who is responsible for strategic project development in the circular economy section at Fraunhofer UMSICHT, believes that polylactic acid will play an important role in the search for innovative bio-packaging. “PLA is a very strong plastic, but it’s also biodegradable,” the chemical engineer explains. “It can also be produced in a way that makes very efficient use of land: From 1 kilogram of sugar, you can produce around 900 grams of PLA.” Dr. Kabasci prefers producing sugar from maize: “At the moment, for example, the majority of the sugar extracted from corn starch is being used as high-fructose corn syrup in soft drinks and other highly sweetened foods. If the sugar content in these products was reduced worldwide, it would free up considerable capacity for producing PLA.” This would not only benefit the environment, but consumers as well − too much sugar is considered a health risk in many respects.

PLA is a good option for the industry sector, as it can be manufactured cheaply. The food packaging sector is extremely price-sensitive – differences of a few cents can be the factor that makes the industry decide for or against a certain plastic. “Currently, PLA is the only biopolymer that is available in the required quantities and with consistent quality levels,” explains Dr. Stramm of Fraunhofer IVV. Its transparency and mid-level barrier properties make it an excellent option for packaging. But until using PLA seems like a financially viable option for the industry, it won’t be worth separating out this particular recycling stream. The lack of proper options for recycling also weakens the argument for PLA’s sustainability from the industry’s point of view. “What we have here is a classic ‘chicken and the egg’ problem,” says Dr. Stramm.

Despite promising research in the area of biobased plastics, we are still a long way from the go al of entirely replacing fossil-based plastic variants with alternatives made from renewable resources. “Besides, biobased plastics are no free ticket to a sustainable future,” adds Prof. Majschak. Quite the opposite: “At it stands, they’re throwing sand in the gears of the existing recycling chains.” This is because “biobased” does not automatically mean biodegradable. For example, PLA is officially considered to be compostable – but for the variants that are durable enough for packaging, this is only possible under very specific temperature, oxygen and humidity conditions. It cannot be done in a domestic composting bin. This creates a huge challenge, as “with the current state of technological advancement, any packaging that is easily biodegradeable would not be able to perform the protective function it was made for,” explains Prof. Majschak. In large composting plants, on the other hand, bioplastics take longer to decompose, so they are less financially profitable: Normal organic waste breaks down much more quickly.

For as long as we still need fossil- based plastics, we will need more solutions for increasing sustainability. In the white paper “From #plasticfree to future-proof plastics,” researchers at Fraunhofer UMSICHT and the Dutch research institute TNO worked together to investigate how we could strike a new balance between reducing plastic and taking a sustainable approach based on recyclable plastic. The paper suggested four strategies for transforming the plastics economy, which is currently primarily linear, into something as close as possible to a complete circular economy. The aim is not only to reduce the use of petroleum-based plastics globally (“Narrowing the Loop”), but to make the future production of these plastics more energy efficient and environmentally friendly (“Operating the Loop”). In order to slow the cycle down (“Slowing the Loop”), we need to find new ways to extend the service life of plastic products. A completely closed cycle (“Closing the Loop”) could be achieved by collecting and sorting ideally up to 100 percent of the plastic that is used, and recycling it into the highest-quality material possible.

Using plastics for longer

Elke Metzsch-Zilligen, head of the Additivation and Durability department at the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, is investigating which additives can be added to a plastic to improve its stability. “Heat, moisture, UV rays – they all damage the material and impair their desirable properties,” she explains. Only with the use of additives can plastics become durable enough for applications such as the electrical and automotive industries. In the Cluster of Excellence Circular Plastics Economy CCPE, six Fraunhofer institutes (including Fraunhofer LBF) have joined forces with industry partners to pave the way for a circular plastics economy. One key section of the cluster is working to better understand and control the aging and decomposition properties of plastics such as PLA. The CCPE is also focusing on developing more suitable and (ideally) biobased additives that will enable long-term use and ultimately either material recycling or a controlled biodegrading process. “The results of our research here are very encouraging,” says Ms. Metzsch-Zilligen.

Additives also play a special role when it comes to reprocessing recycled materials – for example, they can restore desired properties and distribute impurities more evenly in the mixture to avoid unsightly effects on the surface. Or they can be used to remove the frequently unpleasant odor that clings to used materials: If you have ever smelled the inside of a recycling bin, then you know what we mean. The CCPE has developed a method that uses sandwich injection molding to cover bad-smelling old material with a skin of odorless virgin plastic. Special additives in this protective skin prevent the odor being released from the core over the long term – so there is no longer any reason not to reuse this recycled plastic indoors.

The SusFireX and Bio-Flammschutz (bio flame protection) projects at Fraunhofer LBF have proven that not only plastics themselves but also additives can be made more sustainable. In these projects, researchers have developed biobased flame-retardant materials using platform chemicals from biorefineries and cellulose (from sources such as residual material flows from paper recycling). These materials help make highly flammable plastics more sustainable and safer. Up until now, the industry has depended on halogen- or phosphorus-based additives, which are primarily produced from fossil raw materials. “The flame retardants we have developed can be easily incorporated into conventional and biobased plastics,” explains Dr. Klein. And the good news does not stop there: “If we use certain combinations of biobased and conventional flame retardants, we can achieve promising results even at very low concentrations. That not only reduces the ecological footprint, but also improves the plastic’s mechanical properties.”

However, even the longest-lasting product will some day reach the end of its useful life and wind up in the trash. What should we do with this plastic, which has usually been manufactured and processed using a huge amount of energy? According to the German Environment Agency (UBA), over half (53 percent) of the plastic waste collected in 2019 was used for energy, i.e., burned in wasteto- energy plants to generate electricity and heat. Meanwhile, 46 percent went for material recycling, the goal being to turn the used plastic into material for plastic production (recycling). Just 1 percent of plastic waste is currently recycled into raw materials, i.e., broken down into basic materials such as oil and gases – a procedure that is still too complex to be financially viable.

In its waste hierarchy, the German Circular Economy Act (Kreislaufwirtschaftsgesetz, KrWG) gives top priority to the strategy of preventing waste; this involves avoiding or reusing plastic products and packaging. However, this is then followed by strategies that help optimize a proper circular economy. The basic premise here is simple: The longer we can keep plastic in circulation, the less new plastic needs to be produced. “However, this means we need to take the whole process chain into account,” explains Susanne Kroll, group manager for High-Performance Composites and Circular Economy at the Fraunhofer Institute for Machine Tools and Forming Technology IWU. Ms. Kroll is one of the coordinators of the Circular Saxony innovation cluster. Launched in 2022, this cluster aims to bring stakeholders from government, science and industry together to make production and utilization cycles more sustainable, and thus bring the circular economy from theory into practice. “Our very manufacturing processes need to be adapted to fit the concept of a circular economy,” says Ms. Kroll. This can be achieved, for example, by constructing hybrid structures that consist of different plastics and composite materials in such a way that they can be easily separated after use, which means they do not just end up being burned for energy. Consideration must also be given to how the object will be dismantled, for example, by using detachable adhesive joints. Ms. Kroll calls this approach “design for reuse, repair and recycling.”

Reuse must kept in mind from an early stage

In the RE-USE project, four Fraunhofer institutes are already working on producing food and medicine packaging in a way that makes it easier to recycle later. “Much of this packaging is made from plastic composite materials, which provide a reliable barrier that is good for protecting food. Unfortunately, material combinations like these can no longer be broken down into pure polymers, which is necessary for recycling,” explains project manager Dr. Benedikt Hauer of the Fraunhofer Institute for Physical Measurement Techniques IPM.

“In the RE-USE project, we want to cover pure plastics – preferably ones made from recycled material – with a coating such as silicon oxide or aluminum oxide, which acts as a diffusion barrier.” This coating is only a few nanometers thick, explains Friederike Münch, mechanical engineer and research scientist at Fraunhofer IPM: “That’s ten thousand times thinner than a human hair. The benefit here is that the plastic can be recycled like a mono-material, as the contamination caused by this barrier layer will be restricted to the per mille range or even lower.” To ensure that this “superbarrier” is not only ultra-thin but also covers the plastic to a sufficient level in its entirety, the team at Fraunhofer IPM has developed an optical sensor that detects the coating and can therefore perform quality control during production. “By using infrared reflectometry, not only can we see which coating material has been applied, but also how thick the layer is,” explains physicist Dr. Hauer. “The challenge now is to scale this technology so it can also be reliably, quickly and inexpensively used on a large scale,” explains Ms. Münch. Once that has been achieved, the project manager Dr. Hauer can envision a wide range of applications for this measuring technique – such as the production of films for packaging and food containers, and blister packaging in the pharmaceutical industry. Thin coatings, especially of silicon oxide, are also frequently used to optimize physical and chemical surface properties. The new measuring technique can also be used for quality control during production for these coatings.

In project KOSEL, Fraunhofer IWU has demonstrated how the “design for recycling” principle can be applied to automotive manufacturing. “The basic idea was to develop a vehicle platform where components could easily be swapped in and out,” explains Dr. Martin Mausch, head of department for Systems and Technologies for Textile Structures. “That’s been standard for a long time when it comes to airplanes, trains and trams — passenger airplanes are converted to cargo airplanes, for example.” In KOSEL, researchers have developed an open-source, recycling-oriented modular system for an e-vehicle platform, built from particularly durable plastic components. The main modules for the front end, battery box and rear end are connected using fixed interfaces, so individual elements or complete vehicle components can quickly be switched out.

“Approaches like KOSEL are made for the vehicles of tomorrow,” says Ms. Kroll. But are there short-term solutions too? In the Dig-CirclE project, which Fraunhofer IWU is involved in, researchers are using digitalization and automation to analyze and evaluate high-performance fiber-reinforced plastic (FRP) composites from sectors such as the automotive and aviation industries. These plastics are then sent for reuse, repair or recycling, depending on their condition. To make reusing plastic a more financially attractive option, the researchers are also developing efficient repair and recycling processes. “Currently,” says Ms. Kroll, “recycled materials are often much more expensive than new materials.” However, the costs can be decreased through the use of AI-driven diagnostics systems, for example – these can automatically analyze the plastic structures and manage later processes such as recycling.

Artificial intelligence will be a game changer in the recycling process

This is the focus of the AI Hub Plastic Packaging project, a collaboration between the KIOptiPack and K3I-Cycling innovation labs that involves 51 partners from industry, science and civil society. The KIOptiPack team is developing AI-driven tools for designing sustainable products and manufacturing high-quality plastic packaging with a large proportion of recycled material; meanwhile, K3I-Cycling is working to optimize the material recycling process for packaging.

K3I-Cycling is focusing on sorting waste material flows – how thoroughly and precisely can we separate out diverse types of plastics so that they can be fed into single-material recycling flows as far as possible? These days, large sorting plants are using near-infrared (NIR) hyperspectral cameras. “Plastics absorb and diffuse light in different ways,” explains Andreas Keller, a scientist at the Fraunhofer Institute for Nondestructive Testing IZFP. “So that acts like a fingerprint for each type of plastic, which NIR hyperspectral cameras can identify within milliseconds.” However, the NIR sensors are not equally well suited to every kind of sorting task. Black plastic in particular is a challenge for sorting plants.

To solve this problem, K3I-Cycling will be using additional sensors, such as the high-speed thermography systems developed by Fraunhofer IZFP, in conjunction with the NIR cameras. Based on this kind of data for specific plastic types, K3I-Cycling is developing an Artificial Neural Twin (ANT) – this is “a type of digital twin for the plastic that is overlaid with a neural network that can process and manage the stored data and use it to develop new evaluation methods,” according to Mr. Keller. Many different factors may play a role in enabling sorting plants to separate material flows extremely quickly and effectively – including the time of year (in spring, for example, there are always a lot of plant pots made from a certain type of plastic) and which city district a garbage truck visited. “For example, the composition of waste in a pedestrian zone with fast food chains is different to that coming from households,” explains Mr. Keller. Thanks to the ANT, the sorting plant can know what specifically to look out for ahead of time.

KIOptipack, on the other hand, is working to support the concept of “design for recycling” based on material selection, use of recycled materials, and product design, manufacturing, usage and recycling. This will make it possible to balance the many, sometimes conflicting requirements of creating recyclable products and recycling- oriented processes. Fraunhofer IVV is coordinating the packaging elements of this endeavor – its researchers are focusing on how to increase the proportion of recycled material in new packaging, while still maintaining properties such as product protection, a good visual appearance and other sensory characteristics and allowing for efficient processing, appropriate use and safe disposal in a recycling system. The enormous challenge here is making the required data consistently available and using it at appropriate points along the whole value chain. AI will be useful in this context – whether it is used for characterizing materials, configuring machine parameters or supporting humans through assistance systems.

Mr. Keller says that further down the line, the two innovation labs, KIOptiPack and K3I-Cycling, will combine their solutions and use the ANT to create a feedback loop between production and recycling. The information gathered by K3I-Cycling can then be used to improve the design and manufacturing of products. These products will be easier to recycle, and so will result in higher-quality recycled material – thus creating a self-optimizing system. By enabling effective sorting and recycling, developments such as these could potentially keep significantly more plastics within recycling loops than we can today. “Using the sorting system developed by K3I-Cycling across Germany could save 500,000 tons of CO2 equivalent per year,” Mr. Keller predicts.

A sector in flux

Plastic is far more than just tomorrow’s trash, insists Prof. Scholz of the Plastics Technology Center Oberlausitz. If we produce plastic sustainably and work to keep it in recycling loop, it could even make a huge contribution to combating climate change. Unlike materials such as steel or cement, plastic can be produced from renewable raw materials and recycled. Its low weight means it can be transported with less environmental impact, and its durability and stability give it a long service life. “It’s not the material itself that’s problematic, but rather how we use it,” says Prof. Scholz. “And it’s very exciting to make a scientific contribution to the transformation in our approach to plastic.”