Plastics recycling as an opportunity?

07.09.2023

In all areas of our lives, products are consumed that only have a certain useful and service life and have to be disposed of again - be it in the area of housing, food, transport/mobility, at work or in leisure time. Although there is a clear "no" to continuing down the path of a throwaway society, far too much waste continues to be generated in Germany and worldwide. While much is already being done in textile and paper recycling, there are still many unanswered questions about other materials that can be recycled, especially plastics and electronics. With a rising world population, the number of consumed goods is also increasing.

If only the consumption-based values are included, i.e. only the emissions that occur in goods and services, the CO 2 -per-capita emissions are similarly high compared to China; in the USA they are twice as high [1]. The figures vary when production-based emissions are also added, since production is also often done abroad and these emissions are then credited to the foreign exporter. Looking at the largest emitters of greenhouse gases, Germany is ranked seventh in the world, while in the ranking of the most populous countries it is ranked 19th. 1.8 percent of annual CO 2 emissions worldwide are caused by Germany. What can we therefore do to reduce emissions?

Strategies in the waste hierarchy

To reduce the CO 2 footprint, a number of measures have been considered in Germany to propagate climate-friendly consumption choices that affect daily life, such as reducing air travel and CO 2 -intensive travel, among others. According to this study, even a change in behavior toward conscious consumption and targeted, economical product selection could save up to 2 tons of CO 2 per capita per year [2]. In addition, it has been recognized for years that design planning in packaging and product manufacturing can lead in the CO 2 -saving direction. In 2018, a paper was published by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety with a 5-point plan for less plastic and more recycling [3]. In line with European plastic strategies, there are the following priorities:

avoiding or banning unnecessary packaging and products
Promoting environmentally friendly packaging and reusable packaging
Support environmentally friendly product design
Optimize and close material cycles

According to point 1, the best waste is that which does not arise in the first place, as the Bavarian State Office for the Environment already aptly writes. "Avoiding waste not only conserves resources, but also protects people and the environment" [4]. When considering the waste hierarchy as an inverted pyramid, this point is therefore at the top as the most important (Figure 2).

But that also means that we as individuals and also worldwide would have to think in principle with every production and every consumption about what that means for the ecology, the bioeconomy and the resources worldwide.

In the pyramid on the 2nd level follows the preparation for reuse, with which also quite ReUse, i.e. second-hand sale, sharing and leasing is meant. But also an Up- or Downcycling or a use for other application areas are possible. With the strategies for reuse, the manufacturing industry is also required to avoid obstruction and to bring repairable products onto the market, as well as to have spare parts ready and to take this into account in advance in the product design.

Only on the next pyramid level is recycling on the agenda, in order to be able to use used products again as raw materials. Whatever the material to be recycled, it would have to be collected as purely as possible. However, there are a number of obstacles to this: first of all, products often contain combinations of different materials (e.g. textiles on plastic surfaces or products with hybrid structures made of glass, plastic, metal or electronics, to name just a few), for which it is not even clear which waste container they should go into or whether they should not go into the residual waste. To use the plastic portion, the non-plastic parts would have to be removed, like the aluminum lidding foil from a plastic yogurt cup. Part of recycling is to first do this separation. The recycling companies or waste management are left with the more complicated processes. Because not for all plastics separation or recycling procedures exist and there are also often multi-layer systems from different materials, with which must be decided, how to proceed further.

If there is no existing solution for recycling and/or the conversion is in no relation to the resulting costs, one lands with the waste hierarchy in the 4th stage, the thermal utilization or incineration. This produces residual materials (secondary raw materials, slag) that can also be returned to the cycle and consist of both mineral and non-mineral residual materials. In the 5th and final stage of disposal, if the plastics can no longer be processed in any other way and can also not be incinerated, they are prepared for landfill in a facility (materials such as highly toxic and mineral waste, such as construction waste).

In this study, after 2019, plastic recyclates were no longer declared as processed post-industrial waste, but differentiated and the by-products from production and processing processes were mentioned separately. A distinction was made between recyclate production from material streams (with waste code number) and by-products without this number; comparability with previous studies was maintained. The following picture emerges from the data:

Total plastics production in 2021 (with fossil and bio-based raw and secondary materials, secondary raw materials, etc.): 21.1 million tons, from fossil raw materials only 18.7 million tons.
Plastics processing, from fossil raw materials, recyclates, by-product reuse, etc.: 14.0 million tons. The amount of plastic used was 1.4 percent less than in 2019. Recyclate use was 1.65 million tons, plus 0.64 million tons of byproducts for reuse.

Plastics consumption increased to 12.4 million metric tons in 2021, but this was compounded by an export surplus of about 12 percent for plastic products or products with a large plastic content (e.g., automobiles).
99 percent of plastic waste was recycled, with the material/material share at 47 percent and 35 percent when calculated after shredding and washing, for post-consumer waste at 45 percent and 33 percent respectively, the remainder except for 1 percent (landfill) was recycled for energy.
The share of plastic recyclate in the processing volume in Germany is about 12 percent and is used in particular in the construction sector, as well as in the packaging and agricultural sectors. The share of recyclate from post-consumer waste was about 9 percent or a quantity of 1.3 million tons.

Composition of plastic waste

Due to the different life span or even service life for products, not all plastic-containing products arise again as waste in the production year. The service life can vary from days (e.g. food packaging) to 80 years or more (building products). Short-lived products for packaging are found in waste again in 98 percent of the same year. Long-lived products, especially including building products such as pipes and windows, have a different useful life: about 25-30 years for flooring, 40-50 years for windows, and up to more than 80 years for plastic pipes. This leads to percentage variations in the waste stream for the long-life products. In addition, there are still products with a high export share, such as cars, which are often exported abroad after an average useful life of 10-12 years. Only a proportion of around 20 percent of vehicles end up in German shredding plants and appear in the waste statistics.

Thermoplastics account for the largest proportion of plastic waste, namely over 90 percent. These are used in all areas of life and often have optimized physical and chemical product properties that can hardly be compared with other materials. Another powerful argument in favor of plastics is often their low-cost production and thus lower price compared with other materials. However, this is a trend that could change in the future in the context of oil and energy shortages. But since sufficient resources have been available so far, many cheaply produced and widely used standard plastics such as polypropylene (PP) and polyethylene (PE) can be found in plastic waste. These are the very plastics that are often used for short-lived applications, and together with polyvinyl chloride (PVC) account for over half of plastic waste.

PP is readily used for a range of applications such as robust packaging, including food packaging and textiles (e.g. e.g. as hygiene products and technical textiles) The second largest group of plastics is followed by high-density polyethylene (PE-HD) with high density or low-density polyethylene (PE-LD) with lower density, which are mainly used for films and packaging. The different densities come from the number of polymer chain branches, resulting in varied chemical and physical properties. PE-LD is mainly transparent and is used, among other things, for films as we know them from the household, for food, carrier bags, garbage bags and the like. PE-HD, on the other hand, is used for products that do not necessarily need to be transparent, but more robust than PE-LD. We know this material from beverage bottles, plastic containers and numerous household items. However, these materials cannot withstand a temperature load of more than 80-100°C.

Common separation and sorting processes to separate PP from the different PE variants are dry/wet mechanical processes and near-infrared spectroscopy (NIR separation). In addition, recycling processes for PP and PE have been in place for years to reprocess them as recyclate and turn them into new products. As a result, up to 75 percent of both plastics can be returned to the cycle as recyclate. Since recycled plastics can only be used again in the food sector with an EFSA (European Food Safety Authority) opinion, and other sectors such as medicine and cosmetics have stringent requirements for their use, PP and PE recyclates tend to be used for products with high stiffness and impact resistance requirements, such as wheel arch liners, pipes (non-pressurized), corrugated pipes and sheets [6].

Another material that is found a lot in plastic waste is the durable and robust PVC. There are hard variants in the form of window profiles as well as pipes, or in the soft form, including flooring. For many years, PVC was the most produced plastic in the world and was often used in construction. But due to the fact that chlorine can be released when burned, and the use of harmful plasticizers needed for its production, it has become less popular. In recent years, promising recycling initiatives have been implemented, focusing on individual PVC products, such as recycling flooring, pipes or other construction elements [6]. For flooring and windows, there are now even first take-back systems. For mixed waste, PVC is sorted out and mostly thermally recycled. But often enough, for logistical or economic reasons, PVC still ends up in landfills. Since PVC rots only very slowly and it would have to be made first by addition of lime or sodium hydroxide solution landfillable, a storage on dumps is regarded as critical.

With the remaining kinds to be found in the plastic waste (under ten per cent) still a set at materials are represented, which are either more durable, not as plastic waste disposed or by deposit systems extra collected. Polyethylene terepthalate (PET), which is best known as a material for beverage bottles or as a fiber in textiles, accounts for around six percent of the total waste volume. Through the beverage industry's deposit system alone, a high percentage of PET can be collected from bottles and recycled up to 75 percent. However, depending on the chain length of the PET molecule, the recyclates are either reprocessed into bottles, PET films or even textile fibers. A range of sorting methods and recycling processes exist [6]. Other PET products, such as trays or unpopped bottles, end up in plastic or residual waste and are thermally recycled.

Plastics such as polyurethane (PUR), polyamides (PA), polymethyl methacrylate (PMMA) and styrene-containing plastics (polystyrene and expanded polystyrene (PS and PS-E)), ABS (acrylonitrile-butadiene-styrene), acrylonitrile-styrene-acrylate (ASA), styrene-acrylonitrile copolymer (SAN) occur in only a few percent in plastic waste. However, one of the reasons for this is that these materials are mostly used in multi-layer structures, in automotive construction, house building and durable products (ABS, for example, in toys such as Lego) and therefore do not end up in plastic waste as quickly. Depending on the plastic, most have the technical potential to be recycled, but beyond that, other factors such as separability in the product, sortability, and getting contaminants out must be considered. A sorting system like that for PET bottles would be necessary for plastic waste for the different grades, but has not been economically viable. In the total German plastic waste for 2021, only 1.5 percent of recyclates could be found so far.

After the overview of the most commonly occurring plastics in the waste statistics, the question arises as to how the quantity has developed and whether recycling strategies have taken effect. The answer is provided by the statistics of the Federal Environment Agency: in the period from 1994 to 2021, the total amount of collected plastic waste has tripled (Figure 4). According to the Federal Environment Agency study, much more plastic products were consumed than produced over this period, so plastic products were also reused and only then ended up in post-consumer waste (ReUse or also other types of reuse). However, about 1 percent less was also produced when comparing 2021 to 2019. The share of recyclate and reuse of by-products resulted in a 16 percent share of the total processing volume in 2021.

The proportion of plastics from fossil raw materials was 84 percent in 2021 (86 percent in 2019). Calculating the average increase in mechanical recycling for the period 1994 to 2021 yields an increase of about 4 percent. For 2021, one is slightly below the development of the previous years. Possible causes for this were not mentioned by the Federal Environment Agency, but various factors come into consideration, which may also be due to the pandemic with fluctuations in production, raw materials and export.

Figure 5 shows the trend of recyclates from 2017 to 2021 with the share of by-products for the first time in the analysis for 2021. The amount of recyclates from post-consumer and post-industrial waste continued to increase from 2017 to 2021, especially significant for post-consumer waste. Recyclates and by-product reuse are mainly found in construction, packaging and agricultural applications. The reason for this may be the higher hurdles for food and other areas to reuse.

Conclusions from the statistics and trends in plastics recycling development

From the statistics provided by the Environmental Protection Agency, on the positive side, one can see a trend of slow but steady development: more standardized plastics are being recycled and the rate of recyclates and by-products in the production of new plastics is also increasing. Production and manufacturing processes have also been optimized to reduce waste production. Measures such as the introduction of the deposit system for beverage bottles also supported the trend. Germany achieves one of the highest material recycling rates in Europe, with a recycling rate (material and energy) of 99 percent. At first glance, it looks as if the strategies against the throwaway society are taking effect, at least in plastic recycling, and a positive change is being brought about in small steps.

Also, in recent years, attention has been increasingly drawn to climate change, the CO 2 footprint, and the problems caused by increasing production and consumption in the face of resource scarcity. The measures mentioned at the beginning to the 5-point plan of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety are to push new technologies for recycling and for the conversion of the ideas.

But as already pointed out, still more is burned and thus energy won than materially used. While there is more research towards new recycling methods, island projects and implementations to collect and recycle individual building materials (such as initial take-back systems of PVC window profiles), reducing the amount of these plastics in total plastic waste. However, there is still a lack of implementation due to gaps in the value chain, challenges in sorting and logistics. In addition, much stands or falls with the profitability of the recycling processes. A major challenge is the competitive use of recyclates in industry. In most cases, recycled products have higher variations in their characteristic properties due to contamination and impurities. Melting or flow behavior, impact strength, elongation at break, hardness, to name just a few key parameters, can have a negative impact on the manufacturing process, even with minor changes. The use of recyclates therefore also requires comparison with conventional products without the use of recyclates. Other characteristics such as altered odor or color can have an additional negative impact on market acceptance.

Alone the topic of plastic waste in the mobility and construction sectors with short- and long-lived plastic products and the after-effects for decades to come also shows that there is still a lot of disposal and reprocessing work to be done. This also applies not only to the plastics industry per se, but also to plastics, metal and electronics processing companies and many adjacent sectors where hybrid structures are used. The few percentages of fossil energy saved so far through the use of by-products and recyclates in the production of plastics will not alone be able to ensure that the CO 2 footprint per capita in Germany falls significantly. Only an interplay of several strategies and implementations can have a significant effect in the long term.

We therefore see an opportunity to reduce the CO 2 footprint in partnership cooperation between industry and science to consider and further develop new technical solutions from the perspective of economic efficiency. This also includes innovations in product design, the promotion and further development of bio-based plastics, as well as closing gaps in the value chain and the further development of collection and separation systems. This also requires government support in the form of funding projects. Germany could thus achieve a decisive lead in both materials research and sustainability throughout Europe.

This and other interesting articles on the subject of circular economy and recycling, among others, can be found in the specialized magazine "Kunststoffe" (issue 12/2023).

With the congress "Circular Materials - Innovations for the Future" on September 28, 2023, we would like to offer an opportunity to deal more intensively with the topic of sustainability in the field of materials. New solutions for material cycles will be presented and innovations and new project ideas will be discussed. Use the opportunity for networking and be there in Nuremberg!

Literature references

[1] CO 2 -emissions in Germany, USA and China by 2021 | Statista
[2] Federal Environment Agency: Making Climate-Friendly Consumption Decisions with Big Points | Umweltbundesamt
[3] Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMUV): "No to the Throwaway Society" - 5-Point Plan of the Federal Environment Ministry for Less Plastic and More Recycling, https://www.bmuv.de
[4] Bayerisches Landesamt für Umwelt (quote from LfU, Ref. 31, Jürgen Beckmann): Waste prevention for more environm